53131A repair/upgrade - Page 1
Forum section: electronics / repair

author: ZGoode
author_rank: Frequent Contributor
timestamp: August 30, 2024, 01:53:13 am
content: I bought some parts to upgrade the timebase in my 53131A and have some problems. I'm thinking it might be a PSU problem since the OCXO is an extra 1.5A load, but I'd love some input. I am using the 53131A upgrade board from CircuitValley.com with an MV89A OCXO. My counter works and turns on with no problems without this board connected. But when I do connect it the counter turns on with the screen displaying "FAIL: GPIB", and none of the keys are responsive. If I remove the timebase it goes back to normal. Any thought where to start?

author: Qw3rtzuiop
author_rank: Frequent Contributor
timestamp: August 30, 2024, 08:53:19 am
content: I would start checking the power supply output. You can check the voltages on the main PCB.With an RS232 cable you could also get the full error messages.

author: DeepLink
author_rank: Regular Contributor
timestamp: August 30, 2024, 01:28:48 pm
content: The 53131A power supply is very likely to be the problemStart be replacing all electrolytic capacitor right awayEven if the power supply seems to work, it is only a matter of time before it breaksAlso replace the fan, while you are working on itThe reason is that the power supply runs as soon as the power cable is attached (to keep the timebase running 24/7)The 53131A is getting old and all the ones I have seen have there share of capacitor problemsI have repaired many power supply's and ended up making a PCB for a "hard power switch" as I don't use a build in timebase. I'm using a external house 10 MHz referenceschematic of power supply attached

author: TERRA Operative
author_rank: Super Contributor
timestamp: August 30, 2024, 05:00:06 pm
content: I'll 2nd the above. Of the various models of this series I've had come across my desk, they all needed replacement fan and capacitors in the PSU.

author: ZGoode
author_rank: Frequent Contributor
timestamp: August 30, 2024, 06:37:39 pm
content: Ok, that sounds like a good starting point. Seems like this mostly confirms my suspicions so I'll order some new capacitors and start there.

author: ZGoode
author_rank: Frequent Contributor
timestamp: August 30, 2024, 06:52:03 pm
content: I just measured the power rails as shown on page 2-47 of the assembly level manual and all of the voltages are spot on, within +/- 0.05V. Is it still likely to be a PSU issue? I'm still planning on replacing all of the electrolytics since they're known to fail anyways, but if it's a PSU issue I feel like at least one of the rails should measure out of spec.Also, is there some official list out there for the capacitors? I made this list based on the schematic, but want to make sure I am getting the right lead spacing/shell sizes.150uf 400v c147uf 50v c699330uf 25v c3333470uf 16v c202220uf 50v c7220uf 50v c1422uf 50v c910uf 50v c101000uf 16v c1531000uf 16v c1521000uf 16v c1031000uf 16v c1042200uf 16v c102

author: ZGoode
author_rank: Frequent Contributor
timestamp: August 30, 2024, 07:45:21 pm
content: AWell here's something unexpected. I think the MV89A I bought from Ebay is dead. When probing the 10MHz point on the board I get absolutely nothing and my scope does not see any recognizable signal. That might be the problem since all the voltages test within 0.05V of their expected values. I'm going to be ordering a new MV89A from a different seller to test this theory out.

author: ZGoode
author_rank: Frequent Contributor
timestamp: August 30, 2024, 10:54:24 pm
content: Thankfully I had purchased two MV89A's. I just swapped in the second one and it appears to work since it booted up with selftest pass and uncalibrated. It took a little surgery since the second one was missing the ground pin, but I machined a new one from brass on the lathe and brazed it in place of the old pin.Now I just need to either finish my GPSDO or find someone local with one who can help me.

author: Qw3rtzuiop
author_rank: Frequent Contributor
timestamp: August 31, 2024, 06:23:54 pm
content: My 53131a had a fatal high voltage incident with blown ICs and transistors. Thats why I replaced the PSU with another one. I think you just need 5V, 12V and -12V. The 9V of the original PSU aren't used.

author: ZGoode
author_rank: Frequent Contributor
timestamp: August 31, 2024, 07:33:03 pm
content: I might replace the power supply eventually, but it appears my unit is one of the final ones produced of the latest revision, so it actually looks fine. I pulled out all the electrolytics on the power supply and they all tested well within tolerance for the moment.

author: Qw3rtzuiop
author_rank: Frequent Contributor
timestamp: September 01, 2024, 10:02:04 am
content: Quote from: ZGoode on August 31, 2024, 07:33:03 pmYeah no need to replace if it a set of new caps will do the job. I just wanted to show that it can be easier and cheaper to replace the PSU if the original one is badly damaged.The replacement PSU is a Meanwell RPT-60B.

author: DeepLink
author_rank: Regular Contributor
timestamp: September 01, 2024, 04:24:26 pm
content: If you want to run your counter 24/7, as you now have an internal OCXO, do get high quality 105°C long life electrolytic capacitors with low ESR