HP8116 Main Board Layout & Power Supply Adjustments - Page 1
Forum section: electronics / testgear

author: George_Race
author_rank: Regular Contributor
timestamp: June 01, 2015, 11:59:23 pm
content: Need Main Board layout and power supply adjustment for an HP8116 Function Generator.I do have a full service manual, but even going through the Backdating and Updating sections, cannot find the particular layout of this Main Board.Serial Number is: 212 460 1176Main Board Markings: 23412F: 8116 66511: C2228Instrument Built In GermanyVoltages are all over the place, most off by about a volt or better. Have tried to figure out which adjustments are for what voltage, but there seems to be so much interaction between voltages I am unable to follow the proper setup procedure because I don't know which controls do what voltage, and in what order the adjustments should be made.Hopefully someone has a service manual that includes this version of the main board. All I need is the layout and power supply adjustment section to get beyond this problem.Attached are a couple of Main Board pictures. One shows the power supply area with the 5 power supply adjustment pots.The other shows the other group of adjustment pots on the front portion of the board.I think I have downloaded just about every service manual for this instrument, on the web, but none have the right Main Board layout!Any help will be greatly appreciated,George

author: MarkL
author_rank: Unknown
timestamp: June 02, 2015, 03:26:55 am
content: Hi George,Sorry I don't have a layout that matches your board, but in looking at the crazy backdating section in the manual I have, I don't see any major updates to the power supply circuitry.There's one pot (R12) that should adjust -5.25V, +5.05V, and +5.15V all at the same time. That's the only interaction I see, and the rest should adjust independent of eachother.The reference zener that feeds R12 gets power from the +15.0V supply, so it's probably best to start with adjusting the +15V with R24.I doubt they drastically changed the layout. I would bet the regulators on the heatsink still have the same functions (U3 +24V, U4 -24V, U5 +15V, U6 -15V) and you should be able to trace them to their controlling pots. At most there's one resistor along the way. The fifth pot on the other side is probably R12.You can see the heatsink on the A1 board layout to identify U3 - U6.You could also measure the voltages on U3 - U6 if you want to make doubly sure that they still have the same function.I would mark all the pots before trying to adjust them.Note that change #20 changes the -24.0V supply to -23.0V, so you have to adjust for -23.0V.Also, I think the serial number should have a "G" in it, so it's probably 2124G01176.

author: George_Race
author_rank: Regular Contributor
timestamp: June 02, 2015, 11:15:54 am
content: Hi Mark:Thanks for the reply, late last evening I finally figured it out!Yes, the interaction between the 5 volt lines was really throwing me off! I finally figured out that the 15 volt supply was supplying the 5 volt supply chain. The 15 volt line was only about 14 but finally figured out that the 23 volt line controlled the 15 volt line. And yes, my board is marked, 23 volts!So the procedure, I think, is do the 23, then the 15, and then the 5 volt adjustments.Than really seemed to bring it all together.It would really be nice to find the schematic and layout for that particular board, but at least it now has proper power supply voltages.Now I need to find out what is causing the E31 error message. I need to start by troubleshooting the area of the Main Board according to the troubleshooting instructions for E31. So again, the parts layout is not as shown in my current layout and schematic diagram!I will struggle along and see what I can come up with.If you have any idea what particular part would be causing the E31 error, I would appreciate your thoughts.I am going to try to follow their troubleshooting procedure, but the parts layout that they call for the tests on is different!Thanks, maybe someone on here will come up with a diagram and schematic for the board.George

author: MadTux
author_rank: Frequent Contributor
timestamp: June 02, 2015, 11:31:18 am
content: E31:The Timing IC U300 is unable to generate pulses of 5 ms and 25 ms.Possible faults:=> U300Which means finding a happy new U300, which of course is impossible and that's the reason why I quickly sold all my HP 8112/8116s while they were still working (and got quite a lot of money for them)

author: MarkL
author_rank: Unknown
timestamp: June 02, 2015, 01:55:44 pm
content: Quote from: George_Race on June 02, 2015, 11:15:54 amThere's too many possibilities. I would do your plan and work through the troubleshooting as best as possible. If the testpoints aren't identifiable because of the board layout, you'll have to go back to the schematic to figure them out (as filtered by the backdating - sorry!).You could start with their suggestion of the width DAC (and friends) on the control board (10.5 - Width Control).You could also push LCL to get it out of error mode and take a quick survey of what does and doesn't work. You might be able to identify a bunch of broken things that could point to a common problem. Can you get any waveforms out of it at all?I also think it's odd that the power supply voltages were way off. Just something to keep in mind.And there are several U300 available on ebay, if that happens to be the case. It could be anything at this point.

author: Jwalling
author_rank: Unknown
timestamp: June 02, 2015, 03:21:43 pm
content: Quote from: George_Race on June 02, 2015, 11:15:54 amHi George,You might want to ask Dave at Artekmedia if his 8116A manual covers your serial prefix with regards to layout. His manual is excellent, and very reasonably priced.Just a satisfied customer...Jay

author: MadTux
author_rank: Frequent Contributor
timestamp: June 02, 2015, 04:23:11 pm
content: I also have a high res manual on my HDD. PM me your mail and I'll send it to you

author: MarkL
author_rank: Unknown
timestamp: June 02, 2015, 05:57:55 pm
content: Quote from: George_Race on June 02, 2015, 11:15:54 amThis may be nothing, but what exactly was happening that the 23V line "controlled" the 15V line?Do you mean the positive line or the negative line? Or both?Looking at the schematic, both the +15V regulated and -15V regulated outputs are fully independent and don't depend on *anything* else. And I don't see anything in the backdating section that modifies that behavior.I would take a quick detour and measure the unregulated supplies on the + and - terminals of CR1, CR2, and CR3 with respect to ground.And you should check the ripple on those too with a scope. You'll see some ripple because they're not regulated, but the waveform should stay at least several volts away from the regulated rails they're powering.Did you check the ripple on the regulated outputs?Is the line voltage selector in the right position? I once received a piece of test gear that I swore was broken because it ran fine for a while but kept dying intermittently. Turns out someone had set the line voltage to 220V. Good thing it wasn't the other way around.

author: George_Race
author_rank: Regular Contributor
timestamp: June 07, 2015, 12:38:25 am
content: MadTux, my direct email is george@mrrace.com, appreciate your offer very much.Mark, I could not get the +15 even close. After setting the 23 volt line, it was at almost 25 volts, I then was able to swing the 15 volt line from 14 to 16 volts, the control almost centered at +15.Don't see how that could be the case, looking at the power supply diagram, but it really did happen. Maybe I just don't remember correctly what I did initially when I tried to adjust the various voltage controls!I did look at power supply ripple, not a bit on the regulated side of any of the voltages. So the input capacitors of the power supply are still doing a good job. Actually, looks like a couple of the bigger ones have been changed out.Boy you talk about being dumb! ME!!!!!!Yesterday I was moving some parts around in my shop and knocked over the case top for one of the 8116's that I currently have apart. Inside of the top cover is a perfectly printed layout of ALL the CONTROLS ON THE MAIN BOARD! When I get a chance I will take some nice pictures of the two different layouts that I have apart, and post them here, just in case someone like me can't find them. They are both different from the service manual that I have, somewhere there must be some updates that include all the different version. Probably somewhere in a service shop in Germany, where these darn things were assembled.Mark, in spite of the error message, the instrument seems to be working perfectly, although I have not methodically gone through all the many functions it will do. But output frequency and levels seem to be in the ball park, for the most part.Had to work on some other equipment the past couple of days, so have not spent any more time with the problem child. But this coming week it looks like I will have a bit more bench time.Thanks to all for all the suggestions and information, I will follow up on each where I can.George

author: MarkL
author_rank: Unknown
timestamp: June 07, 2015, 01:11:13 am
content: Quote from: George_Race on June 07, 2015, 12:38:25 amOk, sounds like it's not an issue.I'm going to chalk it up to the 23V regulated rail being so high that it created an imbalance somewhere and caused other components to start to turn on that shouldn't be, and it loaded down the 15V regulated rail. Measuring the current would say for sure, but if you have all the voltages in spec and with no ripple, no need to waste any time on it.Glad you found a diagram! I remember that now too on the lid. It's not an obvious place to look!It's also good that things are (mostly) working. Perhaps set it up to make U300 fall into the range of 5ms and 25ms to see if there's an obvious issue that crops up.

author: Smith
author_rank: Frequent Contributor
timestamp: June 07, 2015, 06:35:54 am
content: The operating programming and service manual which is about 10,5 MB has full schematics and 422 pages. The mostly found version is 3,16MB and has only 156 pages.Part 9 describes full adjustment procedures including voltages. Adjustment is a pain in the a$$ with the standard potentiometers. After a lot of fiddling and swearing I replaced every single pot with multi turn pots (and there are a lot!). Its much more stable now too.BTW the fan can be replaced with a more silent version so it doesn't sound like a vacuum cleaner anymore.

author: George_Race
author_rank: Regular Contributor
timestamp: June 07, 2015, 11:43:48 am
content: Hi Mark, that sounds like a very probably cause, as the 23 volt rail was really high.I will try adjusting the width control and see if I can get the U300 back where it belongs.Thanks again for all the good suggestions!Smith, boy that sounds like the manual to get!Any idea where it can be downloaded?Thanks,George

author: Smith
author_rank: Frequent Contributor
timestamp: June 08, 2015, 07:22:16 am
content: http://purco.qc.ca/ftp/Equipment%20Manuals/hp-8116a/8116Aopsm.PDF