IBM PC 5150 repair: the motherboard lives!

Part 2 of the IBM PC 5150 motherboard repair, I continue troubleshooting and get it fully working.
Part 1: • IBM PC 5150 repair: Th...
Part 2: This part!
--- Video Links
My initial testing of this IBM PC 5150 motherboard:
• Mystery motherboard te...
Great resource for IBM PC information:
minuszerodegrees.net
IBM PC 5150 Switch settings:
www.minuszerod...
IBM PC 5150 Technical Manual: (64-256k)
www.minuszerod...
RGB2HDMI: (What I'm using to capture CGA)
github.com/Ian...
Adrian's Digital Basement Merch store:
my-store-c82bd...
Adrian's Digital Basement ][ (Second Channel)
/ @adriansdigitalbasement2
Support the channel on Patreon:
/ adriansdigitalbasement
-- Tools
Deoxit D5:
amzn.to/2VvOKy1
store.caig.com/...
O-Ring Pick Set: (I use these to lift chips off boards)
amzn.to/3a9x54J
Elenco Electronics LP-560 Logic Probe:
amzn.to/2VrT5lW
Hakko FR301 Desoldering Iron:
amzn.to/2ye6xC0
Rigol DS1054Z Four Channel Oscilloscope:
www.rigolna.co...
Head Worn Magnifying Goggles / Dual Lens Flip-In Head Magnifier:
amzn.to/3adRbuy
TL866II Plus Chip Tester and EPROM programmer: (The MiniPro)
amzn.to/2wG4tlP
www.aliexpress...
TS100 Soldering Iron:
amzn.to/2K36dJ5
www.ebay.com/i...
EEVBlog 121GW Multimeter:
www.eevblog.co...
DSLogic Basic Logic Analyzer:
amzn.to/2RDSDQw
www.ebay.com/i...
Magnetic Screw Holder:
amzn.to/3b8LOhG
www.harborfrei...
Universal ZIP sockets: (clones, used on my ZIF-64 test machine)
www.ebay.com/i...
RetroTink 2X Upconverter: (to hook up something like a C64 to HDMI)
www.retrotink.com/
Plato (Clone) Side Cutters: (order five)
www.ebay.com/i...
Heat Sinks:
www.aliexpress...
Little squeezy bottles: (available elsewhere too)
amzn.to/3b8LOOI
--- Links
My GitHub repository:
github.com/mis...
Commodore Computer Club / Vancouver, WA - Portland, OR - PDX Commodore Users Group
www.commodorec...
--- Instructional videos
My video on damage-free chip removal:
• How to remove chips wi...
--- Music
Intro music and other tracks by:
Nathan Divino
@itsnathandivino

[@adriansdigitalbasement]

The EPROM I used is the WS57C49C. It's drop in compatible with the 2364 in most cases but can't be programmed by many programers. I use the DataIO 2900 to program them. pdf.datasheetcatalog.com/datasheet/stmicroelectronics/7919.pdf

[@c1ph3rpunk]

What are those little scope probe clips you snap onto the IC’s? Would love to have some.

[@wildstoo]

I know someone says it in almost every video, but I'll say it again. I really appreciate that you leave your "screw ups" IN THE FINAL EDIT when you miss clues or fail to notice something, rather than hiding it in the edit or reshooting. It makes the whole thing feel much more cohesive and true to life. Thanks!

[@mamayl8592]

It also allows us to often see why the false fixes are incorrect. We can learn from the oopses as much as the fixes.

[@volodymyrzakolodyazhny7740]

Agree.

[@jeromethiel4323]

You learn more from mistakes than you do from successes. Nobody likes displaying mistakes, but those are the teaching moments! You should embrace the mistakes. Because everybody makes them, and they are valuable for learning.

[@TofersCarTales]

The genuine joy you express when it finally frikin works truly warms my retro heart. Thanks Adrian!

[@davidgreen8512]

"It frickin' works" could be on a t-shirt Adrian could sell

[@jowi_24seven43]

Your surgery diagnostics are mesmerising. I wish brain surgery could translate in a similar fashion. Imagine people getting their lives back by replacing a part or resolder the connections.Thank you Adrian

[@MisterZealot]

Gotta love how giddy Adrian gets when a problem is solved. So wholesome. 😅

[@wkjagt]

I repaired the disk controller in my Apple ][ the other day, and when it worked, I said "it freaking works!". I've been watching too much Adrian's Digital Basement :D

[@CATech1138]

@@wkjagtis there such a thing?

[@wkjagt]

@@CATech1138 I've been watching quite a lot, and it never feels like too much to be honest. More like not enough!

[@ovalteen4404]

That 160x100x16 "fake graphics" mode is slightly documented in the technical reference manual. Few people used it because there was no direct BIOS support. You also had to watch the timing in order to prevent snow, like with all direct memory writes in text mode.

[@atkelar]

Speaking of CGA hacking... There was a "256 colors on CGA" listing in one of the old 1980s computer magazines. It did some low level reprogramming to give you a 160*100 or so 256 color mode. Worked fine, but was slow as it can be on an XT so I just looked at it, and never used it for anything. Besides, VGA was already a big new thing too, so nobody was getting new CGA cards back then. Wish I would have kept the code for reference though...

[@jwhite5008]

In case you haven't seen "8088 mph" demo (aka 1024 colors on CGA) it might be interesting to you. It has a detailed writeup too.

[@NEEC1]

Excellent. That parity error message only flashed on screen so very briefly. So easy to miss. But you got it.

[@bryondillon1302]

Good job showing the mistakes that can be made while troubleshooting hardware. A lot of people would just cut this from the video, but I believe that it is valuable to show this kind of thing, because everyone should learn to double check their work, be patient, and take your time. Trying to hurry through with assumptions ends up in replacing components that do not need to be replaced. Keep up the good work!

[@GYTCommnts]

Ahh, my saturdays are not complete without a repair adventure! About the use of the tester and the dead parts case, I like that you included them at the end! I understand why not using the tester while troubleshooting, but it's nice to check later if the tester would have indicated a fail chip. Awesome episode, as always!

[@sarahblikre5674]

I can't get enough of these types of videos. I wasn't around in the 80s but it's fascinating to see the technology that was available and how to troubleshoot it.

[@christopherdecorte1599]

The cyrix cpu is such a beautiful chip you have it rein rezened and use as decorative art or paper weight. Some old chips have a unique beautiful factor to them.

[@aijcadd]

I was related to someone who worked at Cyrix and since he did testing I got cosmetic defects. Overclocked a many of those suckers.

[@chumbawumba1959]

Mad props to you and those that can do board level repair down to caps, chips, etc. I am lucky to be able to replace a PRAM battery in an old Mac, LOL! I think my trepidation is nightmares from the early 80's when I was in rock bands and trying to custom build guitar pedals and other stuff like that. Burnt fingers and creating a mess of solder is all I could get done, most days. Good thing I gave that up and made my career as a Dec Vax guru and later in career a very proficient network engineer.

[@OscarSommerbo]

BTW the white dip "ICs" are resistor networks manufactured by the German chemical firm "Beckman", mostly known i Europe for their paint.

[@ovalwingnut]

This show has all the elements of a good mystery, who dun-it and block buster action film. Good job!

[@allankristiansen8133]

Andrian makes me happy and in a good mood when you can feel his enthusiasm. Thank you

[@BIOS-Engineer]

Before war, I also managed to buy a large box with 8088/80386/80486 damaged boards. 90% of the motherboards were repaired and restored.

[@Cherijo78]

I really appreciate that you didn't name and shame the person who wasn't as experienced at soldering. It's far more important to put out the education on what you really need to do these repairs on certain machines than to shame people. I have a pretty good idea of what video(s) you're talking about because I believe I attempted to watch that video or two as well, and I had to stop at that point for a minute because my brain cringed. I have a 5160 myself that I have been considering preemptively recapping as everything is all original in it currently. I knew the back planes in these things were super heavy and difficult to work with without the right tools, so as someone without a hot air workstation currently, I was already hesitant, and then I watched those repairs and I absolutely decided to put off this repair until I could get the right tools because I could see them struggling so much to do the repair properly. Sometimes the learning comes from watching others struggle, and that can be okay. PS, I very much enjoy commenting at my screen occasionally when I see you miss something, and that's part of the fun for me! My kid just gets embarrassed and tells his other mom that Mom B was spouting off at the Portland Basement Nerd again. 😂😂 Please keep being you because it's absolutely enjoyable and fun to watch!

[@Wikcentral]

Another nail biter. 10/10 results. Your trouble shooting skills are more advanced than many so called professionals that I work with everyday. I run into this at work very often. When you are not 100% familiar with the operation of the machine or the software its super easy to take the long way around to understand what is happening and maybe slip up trying something just to prove fault. Realizing the mistake and understanding what you just saw is a skill many do not have. It is a skill that is underpaid and under appreciated. Thank you for sticking to it and sorting it out and posting such a quick update to this mystery. I once had an incredibly confusing service call when some fire extinguisher residue damaged a bank of dip switches. It made no sense to me why the software was being configured to completely different options not matching the dip switches. I finally removed the dip switch assembly and hard shorted the pins with solder bridges. Before that I had myself convinced that the rom was glitched and I was not going to solve that in the field. PS> I hate it when you bring out the retro chip tester, it reminds me I still have that pcb sitting in my bin of projects waiting for parts ordering and assembly. ;)

[@xianox8]

I hope you take some time to take break this summer. Thanks for the cool content and best wishes from Sweden. /J

[@jcspaziano]

I love watching your troubleshooting process. Ive been a Sys Admin / engineer for almost 30 years and your channel has so much valuable knowledge that far extends the entertainment factor. Congratulations on your channel’s success! Ive been here a while!🎉

[@dionelr]

When I was very young, my dad brought an IBM PC with one of those orange screens home. I was too young to play with the internals of it and I’m pretty sure my dad just gave it away years later. Good old dos days.

[@KameraShy]

It looks like IBM did an excellent service to the community by providing such comprehensive documentation of the computer's internals and processing. Not trying to hide under some false guise to force customers to use their own repair facilities. Like others do now. Stand up for right to repair and thanks to Louis Rossmann.

[@bigdrew565]

They were in the middle of a long-running antitrust case with how they ran their mainframe business. That's part of the reason why they went open source and off the shelf and released all the specs. They just didn't want anymore smoke from the feds. It wound up costing them greatly in the microcomputer market in the end. Don't make the mistake that they were behaving like Steve Wozinak with the Apple II. They just wanted to keep the feds off their ass.

[@ChairmanMeow1]

I just found this channel last week and I've honestly watched probably 20 videos, beginning to end, just in that time.

[@jeromethiel4323]

I am in the process of buying another house. If i get it, i can finally get my electronics bench setup and start doing my own TS&R of retro computer stuff. So looking forward to it.

[@adriansdigitalbasement]

I had to reupload this video, so some comments from Patrons are gone. I'm sharing a few here: @silvestronsbitsandbytes Love love love seeing the logical deduction used in this repair, but it also helps when the docs are accurate! I'm troubleshooting my own 5150 right now with a solid high /CE on U33 lead me to a dead /MEMR line only to find the schematic linking it to a write line on U6 which didn't make sense at all. Thankfully, minuszerodegrees has a footnote explaining that the schematics are wrong, but I spent way too long going in the wrong direction when I should have trusted my instinct. Great job. @JimLeonard The CGA Compatibility Tester strikes again! But hey, you should upgrade to the latest version, added some more tests and color changes you requested. @rdh2059 Adrian: Love watching your work. Here's a question for you. You repair a lot of computers. What do you do with all of them? The notion of fixing them to sell on eBay doesn't sit well with me. Very few young people are remotely interested in retro computers... So back to the question. What do you do with your repaired computers? After all, how many C-64s do you really need?! [[My answer is I give the machines away to people in the local Portland area. I don't have time to pack/ship stuff, so the local folks benefit.]]

[@klocugh12]

> Dead parts tell no tales But you do, and thank you for it.

[@jjock3239]

I learned a lot from your video. I never intend to work on the older IBM boards, I have destroyed all the older computers, after salvaging all the parts I thought would be useful to me. I think your skills in analysis, and the fact that you keep the material in the video where you have gone down the wrong rabbit hole, is really helpful. I am new to the channel, and I have learned a lot here.

[@stompreaper]

I appreciate that you don’t give up Adrian. We all go down a wrong path sometimes and how we handle that defines whether you end up with a success or a failure. Keep not giving up and thanks for leaving it all in and then walking through the mistake.

[@jeromethiel4323]

Ram issues can be problematic on the original IBM since if it detected a parity error (the 9th memory bit is for parity) it could stop the machine in it's tracks. Usually, it would work well enough to display an error message on the monitor, but sometimes not. I forget which pin the parity error comes in on, but it's in the manual and schematic. Check to see if you're getting a parity error by monitoring that pin. IIRC it is an interrupt, and generated by the parity chip on the mobo. Actually designed a test box to latch in the address of whatever was generating a parity error, because soft errors were, and are still a thing. That way when the machine crashed, we would know which bank had an issue, and replace it. Found a LOT of spurious ram chips that way, back in the day. But don't ask me how i did it. I know it was a 4 or 8 bit latch, and a 4 gate nand chip. Used a chip clip to latch onto the processor, to get power, capture the address lines (top 4 IIRC) and the interrupt from the parity chip.

[@jeromethiel4323]

Wanted to call it a Pecker, short for parity checker, but i was vetoed... ^-^

[@familycalendar4930]

With references to the ibm mother board not working. If my memory is correct these pc’s used the loudspeaker to bleep errors if there was no display. Error 100 to 199 mother board 200 to 299 ram 300 keyboard. Your video was very good as a visual diagnostic and explanation of the mother boards. I could have done with this 40 years ago.

[@jwhite5008]

I say cutting that leg was a good call. Logic chips are cheap and abundant, old RAM is more expensive and has limited supply. If you snip a leg of a RAM chip and it happens to be actually working fine you will have an internally good RAM chip that cannot be used in a socket reliably anymore - not the greatest loss but still.

[@custume]

40:16 I was thinking the same, when you show the schematics before was showing that LS 125 going to all the memory, if that line was bad all the memory parity had to be bad and was not, only one data line

[@m1geo]

I was also thinking the same. 😂

[@drrenard1277]

I tried to keep up with the logical process. When trying to decide on leg to clip, I was thinking the parity ram cause if the opamp wasn't working, it should have been more errors. I am happy to know that watching this has helped in my ability to deduce and to know my initial thought was correct. I was thinking that my process was off when you chose the opamp but hey we all make mistakes sometimes. I'm no expert in these processes myself but is fun to see the process of going through them. I wouldn't have thought of cutting a leg though. I probably would have just gone to desolder as only option. I do like that you socketed what was replaced. I find that to be genius. Thank you so much for your videos.

[@VernGraner]

What a fun adventure! Thanks for getting that motherboard back online! 👍🙂

[@ChrisFaulkner]

also, when working with parity memory, if there is a bad chip in bank 3, bank 0-2 is going to be good and bank 4-7 is going to appear to be bad.

[@Colin_Ames]

I finally got around to watching this episode and found it immensely interesting.

[@JohnnyG10178]

the whole time I was scratching my head wondering why you weren't just using the tester...thanks for explaining.

[@patrickbateman3490]

A piece of history recovered !! Very nice !! :) Always a pleasure to see your videos

[@amostake]

That feeling when you hammer at something for days, and then you finally figure it out and fix it. Feels good....

[@tigheklory]

Amazing repair, I bet you are feeling pretty high after that success! Still looking forward to you popping your Coleco Adam cherry. ;-)

[@adriansdigitalbasement]

The Adam must be my most requested thing to do! I have yet to ever come across one.

[@tigheklory]

@@adriansdigitalbasement LOL, I'm sure most of the requests came from me.

[@CandyGramForMongo_]

“We do these things not because they are easy. We do these things because we thought they’d be easy when we started.” 21M ohms. That’s not a speaker, that’s a brick!😂

[@DigbertDayZ]

Brilliant, totally enjoyed this repair 👍

[@ceebee23]

well that was an epic!!!!! oh those were the days when computing was exciting!

[@Stefan_Payne]

Hot air is a wonder machine! And you don't even need to dial it up, it just needs to be reasonably warm, so even 150°C is plenty to help you desolder! Just try it, if you have a hot air station, use it for desoldering jobs at lower settings and you'd be surprised how much better it is.

[@insanelydigitalvids]

Such a great video (part 1 too!) I really appreciate the editing cutaways explaining how you took the wrong path, etc. I learned so much, but I learned even more from the cutaways. Thanks, Adrian!

[@telemedic5142]

I have been watching your videos for considerable time. It’s great to see how your passion for this has pushed you forward and how you have got so much better as you have gone along. What’s better is as you have learned you have shared with us the gained knowledge. Thanks Adrian. Keep up the great work. 😊

[@erikmerchant567]

Great series sir! Saving this set for my future troubleshooting adventures.

[@stub1116]

That was a brilliant video - keep 'em coming!

[@anthonyblacker8471]

Nice work and man the parity chip is probably one of the more difficult errors to narrow down and you having that custom rom really REALLY helped out with the search! It's great to see that mb up and running again!

[@davidsurety2629]

Hi Adrian I have been watching your Chanel for sometime and be never said how amazing I think it is and watch it always love the content and how you produce your content Dave London uk

[@adriansdigitalbasement]

Thank you so much 😀

[@davidsurety2629]

@@adriansdigitalbasement thanks for the personal response I think I found the Chanel by accident and cannot stop watching this was years ago but never got round to telling you how good it is. All the best dave

[@MissNorington]

MS-DOS 6.22 running, and that CGA output!

[@gabrielleeliseo6062]

Freaking awesome, as always. Thanks Adrian!

[@EDemircivi]

crazy work! thank you for doing this video! they’re so educative and improves my reverse engineering skills a lot to be honest❤

[@tony359]

I can't remember how many times I spotted my mistakes while editing my videos and thinking "and now what?" :) Funny moments! Thanks for the video, I would have gone for the logic IC as well BTW :)

[@twocvbloke]

That's the thing about repairing stuff, sometimes we miss the obvious and go off on the wrong path 'til we find it was something simple the entire time, it's part of how we learn in general, making mistakes and knowing to not do that in the future... :) After all, you only stick your finger in a lamp socket once... :P

[@douggibson]

I missed so many episodes, starting with this one to catch up then go backwards from here :D

[@dread1666]

Just a quick tip in case anyone needs to know, in the section with the diagnostic rom and the parity error. That diagnostic rom essentially just pings the data line on the parity chips every now and then. Which makes them easy to check and diagnose with an oscilloscope. (Which might be good to know if you don’t have a CGA/MDA card)

[@ShamblerDK]

Man, I played Ultima V on my 8086 PC running DOS 3.30 for countless hours back in the late 80s.

[@thirstyCactus]

Amazing work! Your tenacity is inspiring.

[@alzeNL]

very enjoyably - amazed at how well all this worked out. great fun. thanks for the uploads !

[@frankowalker4662]

Great repair, Adrian.

[@MicrophonicFool]

I have an external wall outside my studio where I hang all the failed car parts over time. It's called the wall of Shame and Failure. All of my cars are older than any of the computers you work with, so I am usually surprised how long these parts took to fail, so the Shame is not always warranted. I have to asume the 'new' parts I put on will not last nearly as long.

[@ThePoxun]

Paku Paku... those ghost names Stinky, Hinky, Kinky and Blaine

[@DadofScience]

Huge effort and a great win, Adrian.

[@bobsbarnworkshop]

“Fix that mother!”

[@jimstand]

Great video. The long beep followed by 2 short beeps is Morse code for the letter D. This usually means that something is wrong with the Display.

[@k1goolz]

That was awesome how you got the parity error 🎉

[@mdbelt1]

Keep up the great content. Always enjoy the repairs.

[@FindLiberty]

Excellent diagnostics and repair FTW !!! LOL, test it again in a year or two to see if any static damage was introduced (if those are the fussy early CMOS devices. Don't ask me how I know 'bout that...)

[@michaelhaardt5988]

Those were two really excellent episodes!

[@JulienMR]

I just ordered the diag rom for 5150 and 5160, it looks amazing :)

[@watchmakerful]

Not that the parity error was NOT at the VERY BEGINNING of the bank, it immediately should've excluded the logic chips.

[@williamsquires3070]

(@14:07) - You missed it Adrian, it was U88, not U98. Maybe just a brain fart, there. I hope Adrian doesn’t go looking for U98. 😮

[@sparkybrit]

Great job!

[@fnjesusfreak]

I've run MS-DOS 6.00 on a 5160 with 256K RAM, for what it's worth - but that's really tight.

[@jeromethiel4323]

Rammy will eat well tonight!

[@rigues]

I was going to ask why you weren't using the Retro Chip Tester. Thanks for the explanation!

[@soothcoder]

Do you have more scope inputs? It might have helped to have one scope input trigger in the write enable and the other looking at the output signal. If you have a 4 channel scope or a logic analyzer you could have another probe on the input and definitive tell if the output signal makes sense. I find using triggering helps a lot with busses.

[@trex70]

You have so much fun wiith your work. I love it.

[@donaldcongdon9095]

Impressive! Very enjoyable.

[@acubley]

Always love seeing the AMD logo on an Intel board. 😎

[@krnivoro1972]

Nice and informative video, as you keep us accustom to. I think the pic you show at 49:13 it meant to be seen using the composite output, so the chroma decoder is "tricked", giving you an extended color palette.

[@IBM_Museum]

Sad that you missed VCF Southwest (in Dallas at the end of June) after you went to VCF East and are going to the other locations (VCFSW had a hiatus for ten years, but is back strong now!) - Maybe next year!

[@m1geo]

That poor LS125. I was shouting at the TV that it was fine! 😂😂

[@vicroc4]

It was just trying to do its job.

[@MrStevetmq]

I was surprised to see you spend so much time not changing the RAM chip.

[@nicoruizmza]

Dear Adrian, love your work, how u diagnose and the way u look where are the errors/problems. Keep the great content and grettengs from Argentina. BTW, an idea if u what to make shorts: using the dead parts, can u open it and show us how they look inside? so far I only see one guy do this with some newer chips.

[@DAVIDGREGORYKERR]

That is why they moved to DIMM Memory Sockets so as to stop the errors from happening.

[@AftercastGames]

I love that he apologizes to the chips that he incorrectly blames or snips for no reason. It reminds me of when I politely ask Siri to “Add bacon to my grocery list, please.” It’s important to be nice to your electronics. 😉

[@iteachtime]

Thanks! That was awesome as always!

[@adriansdigitalbasement]

Glad you enjoyed, thanks!

[@retropuffer2986]

More computing history saved. 🙂

[@Senux-Video]

super video, super job for future retro pc repair. thnks!!!

[@baghdadiabdellatif1581]

Great work 👌👏👍💯

[@gertsy2000]

Great journey!

[@bytesabre]

Are you gonna run the Area5150 demo in it? That blew my socks off at Evoke last year and if you have a 5150 you need to see it in the flesh. It’s amazing

[@adriansdigitalbasement]

It completely slipped my mind to run that!! DOH! I'll be curious to see if it works with the CGA card from VTEC. It *SHOUD*

[@nneeerrrd]

​@@adriansdigitalbasementthen do a follow-up video :)

[@Zontar82]

Great video as always, was this a PC/XT board? greetings from Italy!

[@dennisp.2147]

Nope. Original IBM PC, (5150) only 5 expansion slots and a cassette interface. The IBM XT (5160) has 8 slots and no cassette interface.

[@JamsterJules]

Love your videos !

[@JeepinBoon]

After breaking my leg and binging on repairing HP power supplies and test kit, I've amassed a generous supply of capacitors which I plan to explode with the 4.2KVA capacitor... Soon as I'm able to carry a 48lb capacitor and 58lb PSU, its gonna be fireworks time

[@fredflintstone8048]

Well done!

[@sefarkas0]

maybe you can add a low ohm pot in series with your test speaker