TSP #16 - Teardown and Repair of an HP 8648C Synthesized Signal Generator

[@mrkattm]

You are a good soul... I have been viewing both your newer videos and you older videos and you have that same enthusiasm as you did when you first started. Fantastic job and thank you for doing this!!!!!!!

[@Thesignalpath]

+Michael Katt You are welcome. :)

[@robertw1871]

Vintage HP mechanical engineering was a work of art.

[@GeorgeTsiros]

What kind of dumpsters are you diving in that you can find frequency synthesizers?! I find half-eaten pizzas and banana peels!

[@apollosgaming]

+George Tsiros My father worked at a medical research company were they would on rare occasion throw electronic equipment away like this. Eventually they started either donating or sent it to recycling.

[@kinghenry1235]

or someone was stealing it and get it later.

[@apollosgaming]

Oh god no, lol. He wouldn't do anything like that. You'd have to be a pretty low person to steal from the place you work at or steal anything for that matter

[@kinghenry1235]

I was referring to someone else, I meant no disrespect to your father or family. I too work at a technological park and yes good things get tossed in the dumpster.

[@apollosgaming]

You're good man, no disrespect taken. I thought you might have been talking about someone else so I didn't take it to heart. Thanks for double checking though :)

[@RobertGallop]

Yes PLEASE make a video on PLL's. I would love to see how that is done and get a better understanding of what is going on inside those black boxes.

[@davideisenberger6197]

thank you so much for making this video! I recently purchased this exact same model on eBay as I had used one for a number of years at my job. But never opened it. It was working just fine before I stuck an antenna on it and set the output to zero dbm to see if my Spectrum An would receive it.. a few moments later, I heard the Fan stop.. turned around and in the window, it stated the power supply had failed. I shuddered to think about what I just had paid for this item... Then I watched your video and now confident that I will make an attempt to repair. I am hoping that it just a fuse (repair persons dream repair!) Once I am able to get all the screws and case off, I will report back... Thanks again! David

[@AxelWerner]

AWESOME JOURNEY through some high end test gear! THANKS A LOT!

[@kevinbeckenham3872]

Very good informative documentary; it is surprisingly what people chuck away.

[@gfx2006]

I just found your channel today and I must say it is one of the best if not THE best on the topic! Please keep making more videos!

[@Thesignalpath]

Thank you. All my Rigol equipment (DMM, Spectrum Analyzer, Oscilloscope, Arbitrary Waveform Generators and Power Supplies) are under calibration. All my Agilent equipment are in 'near' calibration but not NIST certified. My Keithley equipment need calibration. My Fluke and Stanford Research equipment are calibrated.

[@Thesignalpath]

Usually I get the data sheet by searching through Google. For this particular item, it was available from Agilent's website.

[@ElectricEvan]

I think they did apply enough silicon RTV. I don't think HP engineering expected anyone to throw the a machine that cost over 100K when they built it. Incidentally if you are replacing that silicon make sure you use RTV 748 or one of the other electrical grade versions. Most RTV you will find is plumbers grade which emits acid while it sets.

[@ElectricEvan]

+ScribblesOnNapkins The melting point of hotglue is often lower than the operating temperatures you will see on heatsinks.

[@hitechespresso]

+ScribblesOnNapkins 100 k? LOL

[@motafarraghe]

Could you make a video and explain how the power control is done? These instruments can control the power within tenths of dBm at all frequencies.

[@EEVblog]

Excellent score! What brand are those drivers? And where did you get them from?

[@Keith_Ward]

Surprising that cap was able to tear loose with damaging the board or the cap itself. Must have been a cold solder joint to some degree.

[@RickGreenPhoto]

Thank you great video.. I know its been awhile since you did this but can you still get parts and manuals for these units???

[@aknewhope]

Makes me sad to hear these instruments are thrown in the dumpster. :(

[@NebukadV]

As you might have figured out by now: Hot glue is a very handy tool, to quickly get stuff stuck down, but there is a reason, why the manufacturer goes through the trouble of using silicone adhesive. The power supply will get hot and especially the heatsinks, that you glued the mains filter capacitor to, will. You can be sure, that the glue on there will get liquid again, as soon as the unit is running for some minutes. It might be fine for the smaller capcaitors on the output, but eventually these will get hot as well. I know it's a lot more work, but you should really use silicone or some other high temperature (>150) adhesive for this kind of stuff.

[@Thesignalpath]

Luckily the container was almost empty! Otherwise I would have had methanol everywhere. I did check the polarity of the cap, it was shown on the PCB.

[@Thesignalpath]

Yes. It assumes 50Ohm load and displays dBm power for a 50Ohm load.

[@MinnoW12]

Good video, I liked the level of detail you went in to. Thanks.

[@mevmevmev]

That beats all my dumpster finds combined.

[@kevinxbuffalo]

Great video, thanks a lot :) Gotta love dumpster diving for expensive test equipment

[@Thesignalpath]

I have never had a problem with the display except that it does not always show up well on camera because of the backlight. What type display would you have preferred?

[@topherteardowns4679]

Another great video.. (You may have already [i started at the bottom of your videos, now im here], but) a PLL video would be awesome. I look forward to any future repair and tutorial videos you may do. Thank you

[@Thesignalpath]

I would prefer if it were OLED like some of the Agilent handheld units. But this is not as bad as you may think.

[@mathtek1]

Very educational video. Thank you. In addition to that, could you make a video of the frequency multiplier and filter board of this sig gen. This is very interesting.

[@Thesignalpath]

The screwdrivers are from Wiha, a German company. I am very happy with them. I bought them all from Amazon.

[@jeannepindar5672]

I'm happy with mine too. They just feel like high quality, and the rotating handle ends are a nice touch.

[@jvcrules]

Wow, I wouldn't have expected that cap to fall out. Amazing that this was thrown out though. Anyone who knows a bit of electronics (and someone who owns a 3Ghz signal generator certain should!) should have been able to fix this.

[@computerjlt]

I wish i could find things like this while dumpster diving!!

[@Keith_Ward]

Middle east no doubt ... keep in mind his name is Shahriar. I'm fairly used to hearing this accent but I could be wrong. I always look forward to his videos I know that much for sure.

[@JLinnooxs]

Surprised you didn't spot that as soon as you opened it up That high freq sweel was probably arcing

[@Gameboygenius]

Nice video. Except for one thing. I cringed when I saw you put hot glue against a heatsink. Noo! That's just wrong on principle. Apart from the possibility of melting, it will expand and contract when subjected heat cycling, and might even be marginally (even if insignificantly) worse than just putting it at the base of the capacitor.

[@anwarshiekh7142]

I think it rather important that there is only the one Earth connector to the board, otherwise there would be so called ground loops that pick up induced voltage

[@gamccoy]

That was a lucky break with the loose capacitor!! I enjoyed the walk through of the block diagram, as well. Maybe at some point you can do a tutorial about DBm and how you can tie a pure number to a reference? Everyone knows DBs but fewer have seen DBm outside of RF guys.

[@uploadJ]

dBm; decibels relative to one milliwatt (.001 Watt). So, 0 dBm = 1 milliwatt.

[@mehdisediki5852]

Please can you help me to know the equivalent of the two green diode located in the attenuator of hp8648a

[@Fatkuh]

I saw him drinking red wine in one of his videos once, also he has a noticable accent - i'd say hes from France? If so - your the best nearly accent free English speaker from France i've ever witnessed :-O

[@wa4aos]

Very informative video. EXCELLENT! have you ever worked with the HP8640B Sig Gen? It's an older unit but works great and built like an HP Tank. I would Very interested to see you go through one of those. Very Best Regards, Glenn

[@joes5669]

Another outstanding video. I have a suggestion for a future video if you haven't already done it: Proper setup of test and measurement instrumentation. You mentioned RBW and VBW in this video. I'd love to hear your explanation of those settings and how appropriate settings are critical for analysis of the signal. With the power meter maybe do some pulsed RF stuff. You could walk through some experiments with average power sensors versus peak power sensors and then explain the trigger settings/center frequency settings/etc of the power meter. You might even go into oscilloscope probe grounding which is more complicated than many realize (depending on the signal). Thanks for all your hard work on these videos!

[@jeannepindar5672]

I have those same Wiha brand screwdrivers, and they really are high quality.

[@Thesignalpath]

This was a rare find. Normally, most of the stuff thrown out are not nearly as interesting.

[@lexxuzz]

Plz do the review on screwdrivers. Nice repair ! Lucky You ;)

[@UA3BL]

Hello, I hope the topic isn't closed. The output of my 8648C got distorted at frequencies up to 500MHz. The sinus looks like there is a sum of two signals. I suspect something is wrong with the SPST Switches (DG411, ADG413) or with the 1GG3 4202. The signal at the input of Part 08648-60199 is OK but at its output not. Is it possible to get the schematic of this part? Has anyone ever seen it? I don't use frequencies more than 150 MHz so the task is to transfer the signal directly from the input of this Part to its output transistors (I think they are inside 1GG3 4202).

[@PoLoMoTo2]

I watched the Fluke 196B 'Repair' right before this and now I'm just so mad.... How do you get so freaking lucky lol

[@douro20]

It would be nice if they still made these as a single-piece chassis with a removable top.

[@silvermica]

30:19 - diode? I thought, perhaps, a thermistor of some type was used as the load in a thermal power sensor.

[@gotbread2]

very informative video! Just a theory, couldnt the cap has unsoldered itself because it has become to hot? I had such a thing with a filter inductor in a PC power supply.

[@2OQP]

These solder formation on the main cap pads come from high-current arcing. At some point coils and caps can be freed from their pads, by hand. These pads need to be bigger. Beefier leads on the cap is also recommended.

[@2OQP]

Ah Ha. Just what I thought.

[@2OQP]

2OQP The solder joint must have been compromised before the cap dropped. No matter what inertia a cap this size can have. I suspect more that the 'drop' must have started to compromise the solder and then arcing became possible and so forth.

[@SONOFAZOMBIE2025]

2OQP are you having a great conversation with yourself?

[@chansetwo]

Back in the old days they would put metal straps around large capacitors to hold them in place.

[@radek2287]

Great video and solid Wiha screwdriver equipment :-). Do you have 2 specific sets or selected Wiha screwdrivers?

[@santosradiocomunicacao]

I have problem with a generator of the same model. The problem happens when I turn the generator on average 30 minutes, making the use or not of the same it appears the problem. When I try to turn it on, it binds and does the procedure to restart and then displays the following message: "700: REVERSE POWER: PRESS A KEY TO RESET" Could you guide me what I can do and what it can be, given that I am located in Brazil and far from large centers that do maintenance on equipment. Grateful! Alandex.

[@superdau]

Hmm, doing something wrong. No dumpsters around me where I can find such stuff, while you, mikeselectricstuff and eevblog pull out so many cool items from there.

[@Fatkuh]

Maybe they didnt fix it on purpose (although they knew they could) to get an new piece of better more modern equipment approved by their company - who knows... Nice Video! And a nice dumpster you got there obviously...

[@sladjanavlijas295]

Hi, thanks for great video. Can you post schematic of VCO?

[@b2gills]

When you hear a power supply making that horrible noise, TURN IT OFF. IMMEDIATELY. The longer it runs like that, the more problems it will develop.

[@frampthechamp]

The signal generator output is specified in power (dBm), does that assume that it's driving into a 50ohm load? Probably noob question, I don't have much RF experience.

[@TheSoundtec]

Lucky you!

[@douro20]

The oldest piece of test equipment I've ever disassembled was a Dymec digital voltmeter with computer interface from the mid-1960s. It was all-transistor, save a few tubes in the power supply. Depopulating the unit left me with a hundred or so good germanium transistors and a bunch of precision resistors. I still have the display boards, which have a single nixie tube on each and take BCD input. The old Rotron muffin fan in the rear still works but I don't know where I put it...

[@bend0matic]

Shahriar, are your DVM's, Oscopes, Spec. Analyzers that you use, on a regular calibration cycle? Keep up the good work!

[@aa060263]

Good afternoon. I am from Venezuela friend I have n HP8924E, which fails to turn ma 1000, which could be the solution ??? Thank you

[@priestblood]

I have never dumpster dived but if I saw lab gear I would give it a go ,Am never that lucky if I found a pound I guarantee I would of lost ten pounds ,no one ever dumps cool stuff by me

[@omskariyazmaraikayer913]

Dear Shariar . salaams . I just got two units of the same item . I bought it from a scrap dealer .It seems to to work . Something fumes inside when i start . I have been informed that its a bad capacitor . Any suggestions how to go about it. I have not watched this video but i am about to do that.

[@youpattube1]

You mentioned that you use methanol to remove flux fron the PCB. I have only used Isoproyl Alcohol, and am not happy with the results. Have you tried IPA ? And is methanol better ?

[@ElectronicsPubVideos]

Very educative!

[@germanjohn5626]

We used to purposefully disable all test equipment that went into the dumpster or to recycling by either hitting every outside jack with 10kv or physically removing parts of the device. I.E pry parts of the boards.

[@Thesignalpath]

And why would you do that?

[@unelg]

did it make that buzzing sound once you soldered the big cap back? I have a smilar unit (A) which has a very silent PSU . no LEDs on the MB nor on the LCD. should I be able to read voltages from the output pins of the PSU once I hook it the mains?

[@jonahansen]

Dude, you are revealing the fact that you didn't even watch the video in its entirety.

[@mjthebest7294]

9:10 smell test! Hahaha

[@bgdwiepp]

at 23:38 did you spell your alcohol? I also cringed when you plugged in the mains because i didn't see if you checked to put the cap in the right way hehe.

[@superdau]

Btw. where do you get the datasheets from? I got an old HP5245L Electronic Counter (60ies vintage with Nixie tubes!). It works if I feed it a voltage too low with a varic (all the voltage rails are OUT OF SPEC then), but stops working at the rated voltage (when the rails are IN SPEC). I got a datasheet for a later revision (serial prefix 628-), but mine's got prefix 605- and I can't find it... :(

[@oo00xAnathemax00oo]

Thanks a lot for this video.

[@Thesignalpath]

You didn't make it through the video? ;)

[@Electrolab28Ag]

Hi Signal Path, I have a HP 8656B Synthesized Signal Generator that I would like to get the schematic drawing for. Can you tell me where I could find it? Thanks for a great video.

[@stevec5000]

Try using Google.

[@offramp100]

They went to great lengths to hide that bodge wire in the VCO ;-)

[@billybunter9103]

Where is this dumpster you go diving in?

[@devil2005iscool]

What are those screwdrivers called and how much were they?

[@Shitmusket]

how did you know which side went where when u put the polarized cap in ? i must be blind, because i did not see any directions n the pcb itself

[@stargazer7644]

You look for the side connected to the negative on the bridge rectifier.

[@NerdNordic]

Awesome video! Im just curious, where are you from? Cheers! :)

[@gbowne1]

There are several different attenuators that fit this model. Someone probably scavenged the big cap to fix another unit.

[@iknowsstuff]

so the owner of this ting couldn't bother to fix it themselves ......they should be ashamed

[@sdgelectronics]

It's a bit old. Maybe they bought a newer device.

[@gbowne1]

Always use temperature rated silly cone.

[@douro20]

I've heard bad SMPSs but nothing quite that bad.

[@gacherumburu9958]

👍👍

[@OneCoolDude08]

Only thing I find in my dumpster is banana peels, dirty diapers and broken Barbie dolls. I don't think anyone in my city even owns a signal generator, let alone throwing one away. Maybe I need to move!

[@NerdNordic]

Who´s Cone?

[@maynardr6]

I watched the whoooole thing :)

[@Ltb0b]

that's hilarous

[@nlimchua]

let me know if you'd be interested to sell this func gen. I volunteer some of my time doing electronics demos to encourage young kids to pursue science & eng'g....

[@tomislavgasparic8100]

Where is that dumpster? In dumpsters around my hood I see only useless trash.🤦🤷🏻‍♂️

[@yoramstein]

Flux on the capacitor legs directly !

[@adnan2]

You are not watching TV on it. It is just a few numbers and letters all i n all.

[@OneCoolDude08]

Wow, do you get out much? You seem really upset that the 256 X 64 LCD is an STN type instead of TFT. That DMM has many shortcomings, but for the price it's a fair offering. I would also prefer they raised the price $20 and put an OLED display in there, but I'm not going to cry like a little girl over it.

[@daverhodes382]

OneCoolDude08 And yet you comment like a little girl.

[@BruceNitroxpro]

@@daverhodes382, Be a bit more kind, TSP has made so many basic errors in this video that it is embarrassing. No need to rub it in.

[@BruceNitroxpro]

The signal path, I think I've mentioned on another of your videos that your conceptual background is swell, but your actual knowledge of, for example, switching power supplies and BASIC signal tracing is so lacking that it is a bit awkward to watch. This is best shown in this video where you wade in and survive ONLY due to pure luck. I recommend that you watch a master of this subject, Paul Carlson, of Mr Carlson's Lab. He makes his living fixing switching power supplies, but knows the engineering behind how the instruments are designed and used. His knowledge of microwave equipment is probably less than yours, due to your work in this area, but you have much to learn from his work on the subject of power supplies. de KQ2E, Bruce

[@Thesignalpath]

Bruce Nitroxpro Do you realize that you are leaving a comment on a video that is 6.5 years old? Do you honestly think that I don’t or didn’t know how a switching power supply works? Or that I don’t know how the instrument is built and used? While we are always in a continuous mode of learning, some comments are just silly and unnecessary.

[@BruceNitroxpro]

@@Thesignalpath, I apologize for not considering your learning curve. I DID NOT note the time span and do not doubt your technical ability. It was the particular video which compared your methods to that of a switching power supply specialist. I'm sure you wouldn't do things that way again now. de KQ2E

[@jonahansen]

@@Thesignalpath I was perusing the comments here just to see if they are as asinine for an excellent technical presentation by a master that this one is as, they often are for other videos on KZbin. And then I see the one by Bruce Nitroxpro, which made me a bit sad, as it confirmed my fears. Clearly, the Dunning-Kruger effect is at work in this case. Of all the people on KZbin, you could count on one hand the number of them that have your knowledge and depth of understanding of Electrical Engineering, especially RF. I don't understand the motivation of people that need to belittle others, let alone when it is they that don't know what they are talking about. In my assessment, you are THE MAN when it comes to engineering excellence and understanding in these types of videos. Hopefully this can balance out a little of the crap that others leave in the comments, and thanks so much for your fantastic videos. Don't stop, and just ignore the bozos that leave those sorts of comments, as they know not of what they speak.