Measuring the reference diode direct is probably to much a load for the diode . But today many modern benchmeters have a huge input resistance compared to the time this unit was made. Nice video's Fred
Wohooo another repair, time to grab a coffee and enjoy a great video. You always seem to get good deals on used test equipment. In germany TE prices are crazy, and even broken TE sells for ridiculously high prices on eBay.
You're lucky to find a old electronic device at good price to repair on ebay. Here in belgium it's a little bit tricky to do a such opportunity. Keep going to enjoy us doing your videos
At 29:55 you have connected the meters in parallel to compare them. But you should connect them in together at the output terminals, not in series-parallel, to get the best precision (with 10Mohm input resistance on the top meter). With ~1Gohm this effect would probably be negligible. Thanks for the interesting video nevertheless!
The output transistors seem indeed overspec'd. Their heatsinks... not so much. This is an interesting instrument, because it is built like the older analog calibrators (with complex switched divider networks etc.) but with digitally controlled switches instead of mechanical switches.
+Arek R. bez przesady, można czasem coś trafić ale zwykle ma dość wysoką cenę, chociaż już wyrwałem parę fajnych uszkodzonych przyrządów w naprawdę dobrej cenie.
+Arek R. No trochę tego było, z najciekawszych to oscyloskop Hameg HM103(100zł) i Fluke 5101B(500zł). Oba uszkodzone ale niewielkim kosztem przywrócone do życia.
Thanks for a detailed repair log. I have the same unit which turns on fine, but it outputs a fixed voltage no matter what i set it to. The reference runs fine, however I get 4.4V on the DAC output (DAG pin next to the ref. diode, and the testpin that apparenty is DAO, on the right side of the two trimmers for Z101 opamp. The DAC+15 and DAC-15 rails are present on the opamp (pin 4 and 7). I've tried to swap the opamp with a spare, with no luck Do you have any hints for which direction to dig?
What do you mean by "reference runs fine"? What is on the input to Z101? Check the voltages V0 to V10. Check the 4051 multiplexers. Do they change state when you turn knobs? Check the buffering opamps Z102-Z105. Their output is mixed together and goes to Z101.
Thanks, spent few hours on swapping out all capacitors on the power supply... What I meant was that my reference zener diode is running at 6.1483 which matches its label. The V0...V10 ladder seems okay, with 500mV spacing. The Z102-Z105 buffers are outputting around 4v which is close to the voltage on their input pins, from the corresponding multiplexers. They are powered by +15 and -15 volt rail, and the voltage level holds nicely. The Z130 IC apparently gets DAC +7.5V rail, I wonder where it gets the 7.5volts from... I was about to begin troubleshooting the CD4051 array when the output relays started switching like crazy. I figured out that my 5V rail started dropping down to 3V. With the LM309K regulator unplugged the unregulated input voltage jumps back to 7-8 volts. I will try to find a replacement 5V regulator, or use a lab supply for further tests.
I've finally managed to fix mine :) The toll so far is: an AC-DC 5V/2A PSU module replacing the 5V DIG rail due to bad transformer tap; 3x 2N5682 transistors; 3x MJE350 transistors; all PSU capacitors; one missing R307 (10K 5W). While at it, I also swapped all OP07 opamps with some higher end BurrBrown OPA177 units, since I had some surplus. Next in line is replacing the power receptacle with an EMI filtered one, and retrofitting a set of metal oxide varistors for some protection against the spikes. Once again, thanks a lot for the inspiration! I might update your eevblog thread with some details, if you don't mind.
I am glad that you brought it back to life. Quite a number of problems. And a missing resistor? I wonder what happened to it. Of course you are welcome to share the details on the EEVBlog forum.
You must have bought this at the end of the government clean out. I bought a ton of equipment as well, on the cheap, but now, the dealers want an arm and a leg for it.
I guess it must have been good enough to match the rest of the circuitry. It doesn't make sense to make a super stable and super expensive reference, if some other components drift way more.
Measuring the reference diode direct is probably to much a load for the diode . But today many modern benchmeters have a huge input resistance compared to the time this unit was made.
Nice video's
Fred
Wohooo another repair, time to grab a coffee and enjoy a great video. You always seem to get good deals on used test equipment. In germany TE prices are crazy, and even broken TE sells for ridiculously high prices on eBay.
You're lucky to find a old electronic device at good price to repair on ebay. Here in belgium it's a little bit tricky to do a such opportunity. Keep going to enjoy us doing your videos
Always enjoy the methodic way you go about troubleshooting!
Loved it. Good job on the substitutions for the parts. Thanks for sharing. Best Wishes & Blessings. Keith Noneya
Nice video, very interesting, thanks.
I have subbed to your channel, in hope of more interesting repairs.
Greatings from Denmark.
What a great find for the money, great vid...cheers.
Thanks for sharing another interesting repair video.
Thanks for sharing. You have some great videos. Thanks.
At 29:55 you have connected the meters in parallel to compare them. But you should connect them in together at the output terminals, not in series-parallel, to get the best precision (with 10Mohm input resistance on the top meter). With ~1Gohm this effect would probably be negligible. Thanks for the interesting video nevertheless!
The output transistors seem indeed overspec'd. Their heatsinks... not so much. This is an interesting instrument, because it is built like the older analog calibrators (with complex switched divider networks etc.) but with digitally controlled switches instead of mechanical switches.
Thank you for a very good video. I have one question: what have you done with the broken/unsoldered pad?
+Jacek Pawłowski
The connection was fine, but I re-soldered that thing just in case and cleaned the board from that nasty flux around the relay.
+Jacek Pawłowski
Szkoda że u nas nie dostanie takiego uszkodzonego sprzętu :/
+Arek R. bez przesady, można czasem coś trafić ale zwykle ma dość wysoką cenę, chociaż już wyrwałem parę fajnych uszkodzonych przyrządów w naprawdę dobrej cenie.
A co tam upolowałeś?
Ja muszę w końcu dorwać jakiś oscyloskop.
+Arek R. No trochę tego było, z najciekawszych to oscyloskop Hameg HM103(100zł) i Fluke 5101B(500zł). Oba uszkodzone ale niewielkim kosztem przywrócone do życia.
Thanks for a detailed repair log.
I have the same unit which turns on fine, but it outputs a fixed voltage no matter what i set it to.
The reference runs fine, however I get 4.4V on the DAC output (DAG pin next to the ref. diode, and the testpin that apparenty is DAO, on the right side of the two trimmers for Z101 opamp. The DAC+15 and DAC-15 rails are present on the opamp (pin 4 and 7).
I've tried to swap the opamp with a spare, with no luck
Do you have any hints for which direction to dig?
What do you mean by "reference runs fine"? What is on the input to Z101? Check the voltages V0 to V10. Check the 4051 multiplexers. Do they change state when you turn knobs? Check the buffering opamps Z102-Z105. Their output is mixed together and goes to Z101.
Thanks, spent few hours on swapping out all capacitors on the power supply...
What I meant was that my reference zener diode is running at 6.1483 which matches its label. The V0...V10 ladder seems okay, with 500mV spacing. The Z102-Z105 buffers are outputting around 4v which is close to the voltage on their input pins, from the corresponding multiplexers. They are powered by +15 and -15 volt rail, and the voltage level holds nicely. The Z130 IC apparently gets DAC +7.5V rail, I wonder where it gets the 7.5volts from...
I was about to begin troubleshooting the CD4051 array when the output relays started switching like crazy. I figured out that my 5V rail started dropping down to 3V. With the LM309K regulator unplugged the unregulated input voltage jumps back to 7-8 volts. I will try to find a replacement 5V regulator, or use a lab supply for further tests.
I've finally managed to fix mine :)
The toll so far is: an AC-DC 5V/2A PSU module replacing the 5V DIG rail due to bad transformer tap; 3x 2N5682 transistors; 3x MJE350 transistors; all PSU capacitors; one missing R307 (10K 5W). While at it, I also swapped all OP07 opamps with some higher end BurrBrown OPA177 units, since I had some surplus.
Next in line is replacing the power receptacle with an EMI filtered one, and retrofitting a set of metal oxide varistors for some protection against the spikes.
Once again, thanks a lot for the inspiration!
I might update your eevblog thread with some details, if you don't mind.
I am glad that you brought it back to life. Quite a number of problems. And a missing resistor? I wonder what happened to it. Of course you are welcome to share the details on the EEVBlog forum.
Wow, discrete DAC! (Not single package). Haven't seen that since early 80s.
You must have bought this at the end of the government clean out. I bought a ton of equipment as well, on the cheap, but now, the dealers want an arm and a leg for it.
Can you please help me to get those schematics ?
Thank you, great info.
The link is in the description.
Thank you very much.
Interesting that they would had used a bare reference diode rather than a heated one.
I guess it must have been good enough to match the rest of the circuitry. It doesn't make sense to make a super stable and super expensive reference, if some other components drift way more.
pitty the calibration itself was not filmed.
fourty bucks? nice grab!