EEVblog

Dave repairs the Compaq Portable Plus power supply.
And takes a look at the schematic and an unusual old documentation system.
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[@nomeanlol]

All of the warnings about not leaving things flapping in the breeze, it's nice to see a real example of why you don't do that.

[@HighestRank]

The ad presentation was a piezoelectric vibrator. Glue it to tha spot desired to flap in the breeze.

[@ovalteen4404]

They probably attempted to fix it in place with the white glop draping over to the heat sinks. Obviously that side broke off.

[@BillAnt]

Some guys just like to flap it in the breeze, so yeah... ;D

[@jam99]

Dave should not have been so shocked. It is so often mechanical problems with old PCBs. The heaviest component on the board has no effective mechanical support. Where are you going to look first?

[@phillyphakename1255]

​@@jam99I reply 1980s and 1990s power supplies professionally. First thing I check is always for shorted power transistors and diodes, after the sniff test of course. It's easy, quick, and finds probably 80% of problems. Bum connections, bad voltage references, etc, they all happen, but they take attention to solve. A diode check takes no effort.

[@TheDefpom]

Thanks for the mention Dave.

[@Boffin55]

They don't use the 5V6 zener for regulation, that's just OVP protection. if you follow the rest of the circuit, the voltage on the 5V is what is fed back via the opto isolators to the primary side switching, so the 5V rail is regulated by the switching itself (as it's the highest current & power draw).

[@EEVblog]

Makes sense, I should have followed that. The time pressure of trying to finish a couple of videos before going walkabout.

[@yoksel99]

@@EEVblog There is also same OVP protection on the 12V line after 7912. Different Zener PN of course, to be just above the spec'd 12V

[@Alamagosa]

I was going to say that.; almost always the lowest voltage output is used for secondary side regulation. The other secondary which is connected to the primary side is for powering the switching regulator after startup.

[@trevorvanbremen4718]

@@Alamagosa I'm not 100% sure I agree here.. I've found that the highest POWER rail (irrespective of the voltage) tends to be the one that is used for PRIMARY side regulation. The lower POWER rails can therefore use (comparatively speaking) less expensive secondary-side regulation.

[@markcummings150]

@@trevorvanbremen4718 In this case you want to regulate the +5V rail because that’s the most important one for computer chips. The other voltages are not so important. Also in this case you can’t use the other voltages because they are already regulated separately and would be no use in the feedback path.

[@flymypg]

That power supply design brings back nightmares of doing military systems in the '90's, where we had to generate X watts from volume V with reliability R. Which generally meant creating a system with as few stressed parts as possible, but going switched-mode to make the needed power density. For a multi-voltage supply we normally had one rail dominating the power demands, so the primary-side regulator would regulate that output (+5 for the Compaq), and all the other outputs would use secondary-side regulators. One way to look at it is as having a beefy single-rail supply, then tacking on some parasitic secondary supplies. I think I mentioned in a comment on a prior video where even this approach was giving us fits, so we had to do some very sweet custom magnetics to make it robustly meet all the requirements. The switching transformer in the Compaq looks to be that kind of problem solution. Assuming a conservative design needing to survive many power cycles, the presence of that power zener indicates they got it very close to the ideal, and nothing beefier was needed.

[@patmx5]

Dave, I think Sams started publishing Photofacts some time in the mid forties. They were little pamphlets for (at first) consumer electronics like radios, phonographs and TV sets. They'd contain schematics, parts lists and chassis images with parts called out by reference designator, and some voltages and waveforms on the schematics for troubleshooting and repair, and were published periodically in packets of a dozen or so as new devices came out. The radio museum I volunteer at has a nearly complete set of the radio/TV ones; they're stored in binders and probably take up forty or more feet of shelf space in our library. They'd publish annual books with the index list of chassis numbers to enable you to find the correct packet for whatever you're trying to repair. The CircuiTrace seems like it was an evolution of the chassis diagrams, and was (as you saw in the picture) an image of the board with callouts matching the numbered flags on the schematic to make locating the circuit nodes easier. Remember that back in the day, printed circuit boards were new and high tech things in consumer electronics (and nowhere near as robust as they are today when we take them for granted), so I'd imagine that they were very foreign to the repair techs of that time who were used to point to point wiring. As time went on, they came out with additional variants of the publication, with dedicated series for things like mobile electronics and the computer one you were looking at. They are very helpful, except when they are occasionally wrong - then they'll make you tear your hair out.

[@eliotmansfield]

When we were doing third party repair in the late 80’s we always used the sams guide. I believe they were reverse engineered. But as time went on and they used more custom parts it became more difficult and futile trying to repair them

[@Broken_Yugo]

The best part is they're still around, have the whole archive online and your local library may have a bulk subscription with them.

[@eDoc2020]

@@eliotmansfield Yes, the Sam's is the go-to place for technical information on old TVs and radios. People like shango use them almost exclusively. I'm sure some was reverse engineered but certainly not everything. The Sam's for my 1949 Emerson 611 TV says "The cooperation of the manufacturer of this receiver makes it possible to bring you this service" right on the schematic.

[@wb5mct]

Working through college as a tv repairman in the late 1960's I used the Sam's Photofacts packages a lot. Often the first thing ordered from the parts store when a new set came in was the Sam's. They were far superior to the manufacturers documentation (which was usually unavailable anyway) in that the format was consistent with all brands and models and the schematic layout followed the signal path through the circuit.

[@tomadkins2866]

I've been collecting and repairing electronics from 1920 to about 1970 for many years now. I recently came into possession of a huge lot of Sams Photofacts. 14 4 drawer file cabinets and a few boxes yet to be sorted. They seem to be complete, with Sets numbering from #1 up into the 3000s. (1946 to around 1990.) along with mostly complete sets of the book series for Tape Recorders, Auto Radios, CB Radios, Hi-Fi, etc. No computer related sets, though. I'll never lay eyes on 99.5% of the individual folders but, by God, I got 'em if I need'em, LOL.

[@shazam6274]

Sams was a publisher of repair "packets" which had schematic(s), parts lists & later PCB views. They started with Radios & TVs which all had tubes ("valves") in sockets on steel chassis with point-to-point wiring. Wiring was easy to trace from one point to another. When PCBs were introduced in the 50s and 60s, the "tube jockeys" doing repairs couldn't figure them out, so Sams came out with their "circuitrace" (pronounced circuit-trace) with the numbered photos matching the schematics. In the 40s & 50s, radios (and even some TVs) had a schematic in the cabinet from the maker. As things shrunk and become more complicated the schematics were no longer provided. Any technical service information was difficult or impossible to get. This is why Sams came into being and thrived for decades. They reverse engineered everything by hand to avoid any copyright issues. They also believed that their literature was superior to what was eventually available from all manufacturers and stuck with the old "meme" of numbered B&W photos, as you have found with this compaq PC. I worked in a TV repair shop as a teen in the 60s and most had several 4 drawer filing cabinets full of Sams folders. Sams would not sell individual folders for a specific product, they sold annual subscriptions of monthly packets which had folders for a dozen or so different products from assorted manufacturers, most of which you would never, ever need. One of the things they also did was have one folder for a "series" of variants of a product or chassis, which always resulted in confusion of which one you were working on vs the schematic. A Sams folder could be helpful if you had it on hand, but between all the mistakes and the obtuse way of drawing the schematics, they were usually more trouble than they were worth. In the late 60s I found out how to get the manufacturers service manuals, for free! Become an authorized warranty service center for the brand! OFAE (Old Fart Analog Engineer)

[@excavatoree]

The electronic repair shop I used to work at in the 80s and 90s used SAMs Photofacts. (everyone just called it "the Sams," as in "do we have the Sams on that?) If we had the factory manual, we'd use that, of course, but if we weren't the authorized warranty center for a company, we'd use them, or borrow a manual from another shop that was.

[@freeman2399]

I've always loved the look of those through hole resisters. Takes me back to the 80's, my dad had boxes of old server boards lying around from his work, I was so fascinated by all the colors and chips.

[@SaturnV2000]

H.W. Sams has been around a very long time. They are familiar to anyone that worked in television/radio repair. Sams would produce their own schematics/service/alignment info based on manufacture supplied data. They would also tear-down the actual equipment, provide photos, disassembly procedures, and create the numbered "call-out" boxes to locate test points, etc. on circuits boards more easily. They took their own scope waveform measurements and included these photos on the schematic. Hence the "Photofact" and CircuitTrace" trademarks. In other words, they were an added-value alternative to manufacture's service info. Often, the Sams was the *only* source of service info for a particular piece of equipment. "Sams" (as they are commonly referred to) also published tons of books on servicing electronics. A really fantastic, well respected and liked company here in the US.

[@randycarter2001]

In SMPS supplies there,s always one capacitor (I'll call him Mr. Main) where the switching circuitry measures the voltage. All other outputs are what I call implied regulation. Not very precise in that they could be off by 10%. In some supplies they add a secondary linear or switching regulator to correct this. In this supply it's the 5 volts that is regulated by the switching circuitry. If you would to poke around you'll find a feedback path through isolation to the switching circuitry. The fun starts when Mr. Main looses value. The regulation goes completely to pot. To much voltage, to little voltage, works fine no load, totally wigs out under half load, keeps shutting down. And because it isn't regulating properly overheats a burns out. Mr. Main is the first capacitor I check when I work on SMPS power supplies.

[@TheDefpom]

I had a similar repair recently, 240V to 12V transformer had a broken winding right at the post of the primary side! It was attached by old flux! I had to micro solder a short strand on to the winding to re attach it.

[@michael.a.covington]

Sams Photofacts were a staple of TV repair in the 1950s to 1970s (and radio repair a little earlier). Instead of the manufacturer's service manuals, technicians would rather subscribe to Sams Photofacts and get the documentation for several late-model TVs delivered every month (and also buy older ones), quickly building up a file of hundreds of Photofacts. Parts jobbers also kept them in stock so a technician could get one immediately when called on to service a TV whose Photofacts he didn't already have. They covered many radios, virtually all TVs, some other hi-fi equipment, and -- briefly in the 1980s -- a few computers. I have the Photofacts for the original IBM PC and for the Epson MX-80 printer. I consider them collector's items. CircuiTrace simply means numbers in black boxes on the schematics, keyed to numbers in black boxes on the photos of the chassis or PCBs. That's all.

[@michael.a.covington]

Howard W. Sams also published books about electronics and -- this is not well known -- printed the catalogues for electronics suppliers. In those days, instead of Mouser and Digi-Key, we had quite a few regional companies with similar-looking catalogues and with a store in every town to serve the local TV service shops. The main company in Georgia, for example, was Specialty Distributing Company. It had counterparts in other states that were different companies but sold almost exactly the same things. I visited one in Tucson around 1995 and felt like I was stepping back into the 1950s; that's where I got the computer Photofacts.

[@diabolicalartificer]

First rule of electronic fault finding = "check the bleeding obvious numpty" we rarely do though, usually we fart about for two hours checking other stuff. Wish I had a tenner for every time I found a wire loose or a SW switched to off after hours of head scratching and mumbling. Thanks for another grand video me old duck......DA.

[@reggiewallace260]

Just for fun, I though I'd chime in to set the record straight about what was the first IBM compatible PC. I was in the computer business as far back in 1975. I had been selling the Apple ][, Xerox, HP, Osbourne and Kaypro when IBM broke the IBM PC in the summer of 1981. I worked for of of the first IBM dealers in Western NY. It was a great time. However, we all knew that the race to a legitimate compatible was on. Columbia Data Products was the first to strike, shipping their first IBM compatible - the model MPC-1500 - in June of 1982. At the time, Compaq who was working on their machine at the rushed an "announcement" in the fall of 1982 and began taking orders for machine they began shipping in March of 1983. Compaq, attempting to steal Columbia's thunder, marketed their machine as the first "fully compatible" machine. Of course, they offered no evidence their claim was true -- other than saying they determined that in their own private tests. Columbia challenged Compaq to a public test of the machines to see which was the more compatible. Compaq agreed, but discussions about how to do the tests went on and on and no such test ever occurred. In May of 1983 a magazine, "Future Computing" did their own tests and tried to settle the dispute by ranking the Columbia and Compaq models compatibility equally in the category of "Operationally Compatible". PC Magazine and Byte followed suit with their own tests and rankings. Whatever was your opinion, both machines were IBM compatible. Columbia did beat the Compaq to the market by 9 months. Great video and a nice trip back. Thanks.

[@onradioactivewaves]

Compaq were better as an air cleaner than a computer- just open any old Compaq and look at how much dust they've collected.

[@transmitterguy4784]

They were advanced schematics, The "Sams" schematics were a big help in helping me learn how to repair TVs and Radios, and CBs. I still have some at home from the 80s.

[@Xyquest]

Brings back memories. I used to work on these Compaq portables back in the 80s. Now I work on fiber optic communications equipment but no component level work any more.

[@robinsattahip2376]

Back in the day, most technicians I knew would buy Sam's Photofact for just about anything they worked on. The sets were of course all on paper back then and TV stores had big filing cabinets full of them. The manufacturers apparently were not allowed to hide schematics as they do now.

[@IanScottJohnston]

I repaired a 3457A DMM recently which had a knackered transformer......no such luck on a broken external connection though.....ended up rewinding the transformer from scratch as it just didn't make sense to let the old 3457A die.

[@Hogdriva]

Repairs are my favorite pls keep it up

[@twocvbloke]

Funny how the simple faults always get you, leading us down a rabbit hole to nothing, only to find it was just one bloody loose wire... :P

[@RetroMarkyRM]

love this mini series :)

[@OnStageLighting]

Had a "Doh" fault find moment today with a inverter welder. All the stuff so tightly packed that I didn't see a huge scorch mark hidden between components during the visual. It took a fair bit or tracing and metering on the back side until the "hang on a minute, there's a blimmin' great burn on the board down there and a film cap with a black end... "

[@chouseification]

These videos on this Compaq have been great to see, for I owned one briefly while I was in college. This was back when a measly 10 megabit Ethernet card cost almost USD150 and you had to go to a specialty store to buy them (CompUSA and Best Buy laughed when I asked if they stocked them back then). When at that store I saw one of these Compaq monsters sitting in a corner and bought it for twenty Yankeebucks. It had a daughterboard with a 286 CPU on it, and from that board there was a ribbon cable that went right into the old CPU socket, it was so odd to see. It was a monster so I sold it to a friend for the same twenty bucks I paid, but I do wish I had kept it at this point. I have a pretty decent collection of old tech, and that would have been nice to sit next to the rest. :P

[@fieldlab4]

Token ring and 10 Mbps coax ethernet with terminators for the win. One bad connection and the whole network goes down. Damn easy to install though! 😄

[@chouseification]

@@fieldlab4 oh now you're bringing me nightmares of my first job out of high school - doing mostly Quality Assurance at a local factory. It was one of those deals where the company had leased one unit in an industrial park and then later leased a unit two over - so the plant was a hodgepodge of offices and production areas and warehouses all mixed around oddly, with docks coming into the building at places you might not expect. Their network early on had progressed to twisted pair Ethernet for the main office only, as they only had so many ports on the hub/switch (probably hub back then). The production office and other parts in the facility were connected via repeaters and of course there was that nasty coax loop in there; and despite being a reasonably smart guy, one of the banes of my existence was the plant manager (who only lasted a year or two) was some odd guy who needed to rearrange his office every few weeks; and when he would do so, of course he would disconnect that cable from his computer - killing line termination and dropping that entire segment. D'oh! It was only when I raced into his office with clear anger in my face asking him why he insisted on dropping the network so often when people had shit to do that he finally grasped why we kept telling him to NEVER EVER disconnect the cables from his PC. Of course he was "a Mac guy" so was completely clueless that support teams don't ask, they DEMAND, and if you don't obey, you lose. :D

[@fieldlab4]

@@chouseification And remember Gateway Computers made in South Dakota or some such nonsense, which came in big black and white cow print boxes? My nightmare nutjob manager was Dave Matthews who ran CUPS into the ground soon after firing me for failing to set up my first gateway properly after successfully installing an entire serial networked pc system in a credit union. May he rest peacefully in hell. This was the earliest days of PC ethernet and everything was running freaking MS-DOS. I don't even remember who made the network drivers.

[@chouseification]

@@fieldlab4 yes I do; I'm from Minnesota myself, so it was one of the big mail order companies making great gear in the mid 90s (the other one was Zeos, who were local to me - so I went into their store regularly). One of my college roommates had a 386 with the VL bus for his hard disk and video - that was a Gateway and he kept the giant cow print box on his closet shelf, so we saw it regularly and sometimes would even moo at him when he opened the door, as you could see it in the background. :D

[@Rusty_Gold85]

I found from my telstra tech days to very carefully nick the cable sheath in 3 diameter locations ( to leave the conductor safe ) and allow the sheath to pull off . Good job getting in there by the way

[@harimadhavan1712]

Great stuff. I wished if someone would do your voice over the parrot in Aladdin 😁

[@bobweiss8682]

Sams Photofacts were aftermarket service data for consumer electronics. Anyone who worked in TV/Radio shops in the US would be familiar with them. Instead of simply redrafting the manufacturer's service data, they actually reverse-engineered it from production units. A typical folder for a television chassis would have the schematic, parts layouts, test point locations, parts lists (giving OEM p/n, as well as several aftermarket cross references), assembly/disassembly instructions, alignment procedures, dial cord or drive belt stringing diagram, etc. The best thing about them was that unlike the various OEM manuals, they were all laid out in a standard format, with signal flow from antenna to CRT arranged left to right, with voltages and key waveforms marked right on the schematic. They released these schematics at the rate of 5-6 sets per month, with each set having folders for maybe 5-6 TV sets, and a handful of radios, stereos, etc. Every decent TV shop had a subscription, and a library of photofacts that took up several 4-drawer file cabinets. They published a periodic index that you could use to locate the proper set and folder number from the model number of chassis number of the set dropped on your bench. Pulling the appropriate folder out was typically the first step after popping the back off the set and looking for obvious faults. They started in the late 1940s, and were still being published into the flatscreen TV era, I believe.

[@MrCapacitator]

Started in 1946 and their website does show a pic of a flatscreen www.samswebsite.com

[@volodymyrzakolodyazhny7740]

A funny moment with DaveCAD at 11:20, when Dave "got one right". :)

[@FindLiberty]

Nice, old school.

[@pahom2]

Multi stranded wires are actually less reliable and tend to oxidize and decompose in few decades. It doesn't requires much moisture in the air to rot thin strands because they have more surface area. I've seen old coaxial antenna cables that just lose connectivity in their braid and when you cut the outer insulation the braid just spills out in tiny pieces.

[@lasersbee]

16:06... I would have added a small piece of silicone wire to the broken lead to 1) simplify re-connecting to the Pad. 2) relieve the stress on the XFO wire due to any future vibration problems.

[@PatrickPoet]

I used to use Sams Photofacts for television and radio troubleshooting in the late 60s into the 70s. They were high quality schematics (even with corrections from manufacturers and notations about revisions) with test point voltages and scope traces. They were available for most about anything, and you could get them at electronic parts houses, or order their catalogue and get them by mail. The best schematics from manufacturers had all that anyway, but most manufacturer schematics were far from the best. I'm surprised most don't know what they were. I headed off into other careers and lost track.

[@eDoc2020]

As soon as I saw the 'normal' diode test readings I was pretty sure it was an open in the transformer. It's nice that the break was right at the board connection and not buried inside the core.

[@jaybird57]

Nice job!

[@chrispollard6568]

Shine a bright light through the board.

[@electronic7979]

Helpful video. I liked it

[@KarmaElectronics.]

did a good job of gluing and strapping the caps down .

[@W4BIN]

Good show. It was single core wire because it is the enameled winding wire. Ron W4BIN

[@GalileoAV]

IDK why but the "It's all higgildy-piggldy, it's all over tha shop" rant at 1:15 was hilarious. It's always fun to work on electronics that seem like they don't want to be worked on :D

[@GeoffSeeley]

Hard core fix!

[@fieldlab4]

When I was a kid I hung around in a hobby shop that had big file cabinets full of folders for about any type of TV or radio you could buy. All Sam's Photofact. I think the CircuiTrace was just a map of test points. Who knows, some boards might have been labeled. Of course Sams is still around, right? Computer language and EE books.

[@PL-VA]

The old eevblog is back!

[@peep39]

I repaired the smps on an HP 35660A. That has multiple rails as well, and one of the voltage comparators (LM339) was blown, giving a constant high output (forgive my memory). The result of that condition was a constant shut down signal being given to the oscillator. Once I fixed that, and the machine went through POST, it gave a memory error. I ended up replacing 32 memory modules (M5M41000BP-10) with sockets and new ICs, and then it worked. A very satisfying result, as I am only somewhere between an amateur and novice. NO idea why double failures, as it was an ebay item, but I'm thinking voltage spike

[@Herby-1620]

Photofacts date from 1946 (I had one in folder #1, an Arvin Radio). For most of the time they were related to vacuum tube devices and their troubleshooting. They were published on a regular basis for servicing electronic devices. If you had to "service" an electronic device (alignment, etc.) there were VERY useful. As things got more integrated with ICs and the like and more and more circuit boards, servicing got relegated to "swap and replace" methods, and fixes like the one you just did got left by the wayside. Time marches on.

[@WacKEDmaN]

geeze...coulda been there all year trying to find that problem... nice find Dave!.. its usually always the simple things!..altho that didnt seem like a simple fix!

[@trevorvanbremen4718]

Edit: This is all covered in a PRIOR post... I didn't see it until too late! Somewhere around 25:30 you're kinda 'complaining' that they didn't use a linear regulator on the +5V rail (while they DID use one on the +12V, -12V and -5V rails)... The answer, of course, is that the +5V rail uses PRIMARY side regulation by way of the TL431 voltage reference. If the +5V rail falls too low, the ENTIRE SMPS duty cycle is increased (which implies that the INPUTS to the +12V and -12V linear regulators will also increase!) The 'effective' degree of voltage regulation on this PSU is, in many ways, BETTER than that of a modern ATX12V PSU. (Modern ATX12V PSUs deliver TRUCKLOADS of amps on the +12V rail, negligible on the rest and don't even HAVE a -5V rail). If ya go one step further and look at SERVER class PSUs, you'll find that they have a +5v standby (mostly used for no more than to power the 'soft-on'), a very small -12V rail (barely regulated at all), and a HUGE +12V rail that often exceed 100 Amp! .

[@frugalaudio]

Back in the day, every local Radio/TV repair shop had a Photofact subscription. They provided schematics & service data for most mass produced electronics. Easier I guess, than trying to get that info, piece by piece, from dozens of manufacturers. Still widely in use when I started my electronics education in the '80s.

[@SeanBZA]

Wire that hard to get in, I would simply cut a short wire and put it in the hole, and do a soldered joint up high where it is easy to get to. Best to put a blob of flexible gunk to hold that transformer down to the heatsinks all round, to keep it from vibrating any more. Only the 5V rail is regulated, the rest will be much higher voltage, so the regulators to handle the extra voltage when unloaded. The one chip switchers to get the linear regulators out were still in the future. 5V6 zener is there to go short circuit, hopefully, on loss of regulation, and short out the supply. Only thing is they also like to leak slightly and then fail as open circuit.

[@joegee2815]

My BM786 is on route to me as I watch this. The anticipation is killing me.

[@techy9937]

brings back memmorys and how much i miss doing this type of work.love the technical terms there it is the little turd.

[@CandyGramForMongo_]

Bravo!

[@doogie812]

That computer must have very low hours. I used to fix those power supplies back in the '80's and they were cooked! A number of them the circuit board had become conductive. I sent a number of back into the field with gaping holes in them.

[@EngineeringVignettes]

FYI, there were 2 main 3rd party service notes publishers used in North America in the 50 - 80's era. Sam's Photofacts was one. The other was Riders. I believe Sam's won out in the end, I do not see a lot of Rider's service notes later on in that era. There could have been more competitors; I am not aware of any... Major Radio brands like RCA Victor were pretty good on publishing service data and service notes (books really) on their products as well. I have several of them in my library covering the 1929 to 1940 timeline.

[@Deadwindshadow]

"Both of those are cactus" lol really got me

[@perhansson6718]

Thanks for the look at the schematic at the end, I just finished watching your EEVblog #600 - OpAmps Tutorial yesterday so this was a nice coincidence! Is the schematic available somewhere for download?

[@clems6989]

I hate troubleshooting SMPS circuits. They are always like this, cannot get to anything....Good job old man !

[@ulwur]

Wow. That Brymen autoranges really really fast!

[@rtyhgfplmkoi4784]

It's always the last place you look , cos you don't keep looking once you found it.

[@IlBiggo]

Irrefutable logic there :D

[@vidasvv]

Guess ur too young Dave but SAMS was great to have. Back in the 70's before the internet getting info was difficult and SAMS was about the only way to get schematics. As my dad use to call us "ur just a young punk"! Very surprised that you never heard of SAMS. TNX 4 another great video !

[@rikvdmark]

Nice one :)

[@heikovanderlaar3780]

You said you'd link it in but you didn't link it in. I will never forget this betrayal.

[@NebukadV]

Please stick the transformer back down with silicone adhesive to the headsinks, as it was before. Next cable, that breaks, might not be fixable anymore. As you can see, it was originally fully stuck down to the heatsinks on 4 points, so it should have been held in place pretty well. The silicone must have cracked maybe during shipping and after that the cable broke loose over time.

[@ericmoeller3634]

I love you dude no homo you where suggested to me on my home page on my KZbin account you have tought me a lot more about electronics i new a lot but sense i was a kid but have internet i have learned a lot more about electronics sense i have subscribed to your channel

[@__--JY-Moe--__]

nice! they sell a 8K PU round trip for 80US!! talking about some wild stuff! their on e-bay! good luck neighbor! real quality! made in U.S.

[@andymouse]

cool.cheers.

[@williamsquires3070]

(@1:55) - Did Dave say he had a stocking? That’s nice. That way he can keep his footsies nice and warm!

[@ianc4901]

I was waiting for the shower of sparks when you switched it on while it was sitting on that ESD mat ! I cannot figure out how it can be non conductive if it is able to discharge static.

[@EEVblog]

kzbin.info/www/bejne/bXepo42ibt6gfNk

[@piwex69]

David, check Shango066, he uses SAMS PhotoFacts for each and every bit of gear from 40', 50', 60' and 70'. I have never known they had survived into computer age thou.

[@zero0ryn]

Hey Dave, You were saying that it wasn't very good the way the it appeared to have no regulation for the 5V rail, well the Switching chopper regulates it. That's a really cool thing, compaired to some slightly more modern PSU's which regulate the 12V rail and just assume that with less turns on output transformer for the 5V rail that it will follow that if the 12V is good then the 5V is good also. This is great till the Electrolitics on the 12V rail go leaky and the PSU is working over time trying to get the 12V rail up to voltage. All the time the 5V rail is near 10V as a result. (This cannot happen with your power supply). I had this happen in a AT power supply and it blew up everything in the system. HDD Floppy, Mouse, Keyboard, CPU but oddly not the RA,. Multi IO Card and VGA card all stuffed due to bad PSU design.

[@gamerpaddy]

i got a strange problem wih 78xx linear regs. i put a 7815 and 7915 +-15v psu in my design with several ne5532 opamps and when i power it up, theres like a 25% chance of the positive rail not starting, it gets pulled to -0.7V. and stays there. but most of the time, it just works like it should

[@Petertronic]

Will there be a video about the BM786?

[@JohnSmith-xn3fr]

what a soprano ! you should sing at the Boy Quire in Vienna :)

[@martinda7446]

The transistor was made in Manton Lane Bedford by Texas Instruments in the factory they built and opened in 1962. The jedec coded semiconductors were not seen so much and nearly everything was pro electron coded..Apart from the ubiquitous 2n3055..Maybe I'm talking bollocks, but it's how I remember it.

[@Daveyk021]

Dave, what I found most interesting is that you never heard of SAMs photofacts, TV shops over their lifetime would have collected thousands of them. Once pack, had the main schematics you were looking for a given TV and then usually had several schematics for lesser ones. There was a printed manual that you would look up the MFG and Model and know what SAMs to get out of the file cabinet or to buy from the local TV parts supply shop (in Central, Pennsylvania, that would have been Cumberland Electronics). Quite frankly, myself, I haven't thought about SAMS in a long time. I figure SAMS went bye bye when manufacturers stopped releasing schematics in the mid-late 90's. But back in the pre-throw-away day, it was almost impossible to fix a TV or stereo without a SAMS. they were readily available, so why not? The quality and layout of the schematics, to a technician, were excellent (you made fun of that part). I didn't realize they did computers too. Wow, too cool and a wonderful look through the way-back machine.

[@eDoc2020]

I have a feeling Sam's might not have been a thing overseas. I'm not sure though.

[@MikeB_UK]

After all these years and you didn't "Thou shalt test voltages" first. Oh dear, diving into component checking first... Maybe time to think about retiring or at least handing over to young Dave. :)

[@Vbeletronico]

A friend of mine designed several power supplies for Compaq. I don't know if he did this one, though.

[@chrisroberts2266]

lol the layout isn't that bad for testing! You should see the ones I have to work on, like ones from Sony Pro

[@temporarilyoffline]

Sweet As! I just got one of these and did a video.

[@garethevans9789]

I've never seen so many diodes on one circuit, I hope they got a good discount. Components made in Britain.👍

[@groovejet33]

Yeerrrrrrrrrr!! 8mins of bonus video......Yippie

[@robertmcfarland9184]

Such a great Series. I own a Compaq Portable Plus. Where can I find the Schismatics. I've looked but have had no luck but Service manuals, and Maintenance Manuals.

[@tahustvedt]

Good quality components on that thing to still be good and clean. Glad it wasn't a broken transformer. That would have been sad.

[@kyoudaiken]

LOL This thing will never comply with 80PLUS ratings. :D

[@markm0000]

It complies with 80NEGATIVE ratings xD

[@andrewmburga]

Dave has already bent the tip of his pointer stick, just like the last one

[@augustinchenault9981]

Wow SAMS made schematics all the way into the 80s? I’m restoring a 1950 TV and I’m using the SAMS Photofact

[@jimmy8653]

Sams is great fixed several radios

[@russwilliams8274]

So... in the end... the only thing wrong with the machine was, like, the third component that power reaches from the mains input? Which meant no negative DC rails, which meant no Power Good signal, which meant the CPU was stuck in a reset loop, which meant no output from the graphics card, which meant no CRT display...

[@rogeryoung2567]

Your saying it so follow it ,you know you cant check a semiconductor in circuits unless its powered on so either power it up or pull the components to be tested !

[@CiscoRedstar]

I find about 95% of my electronic repairs turn out to be mechanical in origin

[@Audio_Simon]

Why run the -5V reg off the -12V one? Won't the total power dissipation be the same as running both from the higher volt source? Only the dissipation will be more weighted to the 12V reg? Maybe a good opportunity for a video on best ways to power share across devices?

[@Fry09294]

I have one of these whose power supply I think came loose and shorted out against the metal chasis, I'm hoping I can just replace it.

[@thomasleerriem6872]

A switching power supply that fails, what a surprise ^^

[@senorjp21]

I'm pretty sure you know Cody's Lab... Cody got kicked out of college. Please consider making a short video about why Cody should be re-admitted so I can compile it with others and send it to Utah State University.

[@EEVblog]

I have not heard about this. So have no ideas of the details.

[@MrDoneboy]

Besides the cap that failed, of course?

[@christopherhall2635]

That was an interesting video :-) Went to get a BM786 but you have already sold out :-( When will you be getting more stock please?

[@UpcycleElectronics]

In this episode... Dave drops a Dora. Mighty fine Australian wine. Fresh probe porn. Complete tug test. Rated PG.

[@jacobcochrane987]

Where do you find that service manual? I am working on repairing the power supply on one I just picked up.

[@ukaszsmoa8416]

Is the solder mask that is on the traces at the bottom of the pcb comming off? It looks like paint after chemical paint stripper has been applied.

[@Blayzn18]

That meter is so big my brain told me it was photoshopped at first

[@clintfisher]

Sold out of the BM786 already? :) How long did THAT take?