HP53132A with incomprehensible fault - Page 1
Forum section: electronics / repair

author: cosmo little
author_rank: Contributor
timestamp: February 19, 2025, 10:14:28 am
content: My HP53132A counter worked for 15+ years with no problems. About 3 months ago, it started showing "ROM fail" message on power up. I also noticed that sometimes it was reluctant to start when the standby switch was activated.I assumed that both problems were due to bit failures in the EPROM memories. I ordered some new EPROMs from a Canadian called EPROMPRO, using the latest code from an EEVBLOG contributor.On fitting the new firmware, the "ROM fail" message had gone away and the counter works correctly. However the occasional reluctance to power up was still present, evidently nothing to do with the firmware.After a great deal of investigation, I discovered:1/- Provided the unit is kept permanently connected to line power, it powers up every time.2/- If the line power is disconnected , even for 1 second, it goes into a stuck state where it will not power up. It can take many hours connected to the line power before it starts to recover. It then starts intermittently to power up, and slowly improves until it powers up ever time.3/- In the stuck state, the switched supplies SW+12V, SW-12V, SW+5V all turn on normally. All other supply voltages appear normal. I have checked every tantalum decoupling capacitor for the correct voltage.4/- In the stuck state the processor runs as can be seen from activity on the address and data lines. The processor clock is at the correct frequency. Manually shorting the reset line to ground does not result in a power up. Looking at the ~OE lines to the EPROMS, the processor only runs from bank 1 in the stuck state. There is no attempt to write to the display serial controller.It seems that the processor is getting stuck in a loop, perhaps due to a failure in another chip that it needs to address as part of the start up sequence.I must admit that I am baffled by this problem. Apart from changing the processor and RAM chips, I see no way forward.Has anyone seen this sort of behavior before?Thanking you in advanceCosmo Little

author: wn1fju
author_rank: Frequent Contributor
timestamp: February 19, 2025, 12:41:10 pm
content: You are not alone!!!When I received my HP 53132A (I inherited it from a relative), it threw a ROM checksum error. I purchased a new set of ROMs and programmed them (an examination of the old ones showed one bad byte right at the end of the code). All was well.But then I noticed that occasionally the unit would not start when I pressed the power button. However, it would always start on the second try. I don't leave the counter plugged in on standby and I would say that this no-start behavior occurs about 1 in 15 tries or so. I didn't pursue it any further since it did always start, but I would be interested in whatever conclusions you find.Sometimes, I guess things just happen. Like my HP 34401A DMM which sometimes switches itself from DCV to ACV after an hour or two of idle use. Or my HP 3326A function generator that once, and only once, started up and threw a numerical error code on the display that wasn't even listed in the service manual.

author: TERRA Operative
author_rank: Super Contributor
timestamp: February 19, 2025, 06:33:20 pm
content: Are the electrolytic capacitors in the power supply original?They tend to wear out as the PSU is operating whenever power is applied to the mains plug, even when the counter is turned off at the front panel.I have replaced leaky caps in a number of these units now, might be time to do yours.Bad caps will let switching noise through to the sensitive bits, potentially causing erroneous operation.

author: cosmo little
author_rank: Contributor
timestamp: February 20, 2025, 03:13:40 pm
content: Thank youI will measure the noise and ripple on the power supply outputs, and see if this changes with time. This might be the answerCosmo Little

author: TERRA Operative
author_rank: Super Contributor
timestamp: February 20, 2025, 04:35:59 pm
content: With equipment at this age, don't waste time measuring things, just replace all the electrolytic caps straight up. If they aren't bad now (they 99% are) they will be bad soon.I'm at 3 for 3 with leaky caps in these counters so far, and two of the three were just flat out not working until I replaced the caps....

author: Andy Watson
author_rank: Super Contributor
timestamp: February 20, 2025, 05:03:40 pm
content: Quote from: cosmo little on February 19, 2025, 10:14:28 amI'm not familiar with the 53132A, however, some of the HP equipment that I have does not completely power-down. The oscilliator is kept permanetly powered as long as therre is mains present (so that you don't have to wait for it to warm-up). Perhaps your oscillator is going a little soft and is reluctant to start up.

author: Laval
author_rank: Regular Contributor
timestamp: February 20, 2025, 07:19:57 pm
content: Quote from: TERRA Operative on February 20, 2025, 04:35:59 pmThis is consistent with what happened with my 53131A. I suspect it has the same power supply as the 132A. Once I replaced the electrolytic capacitors on the PSU, it worked just fine. Granted, there was probably only one or two that really needed to be replaced.

author: TERRA Operative
author_rank: Super Contributor
timestamp: February 21, 2025, 03:10:03 am
content: Yep, 53131A, 53132A, and 53181A all use the same power supply and most other parts too besides mother board.

author: Zucca
author_rank: Unknown
timestamp: February 21, 2025, 07:32:50 pm
content: Quote from: TERRA Operative on February 21, 2025, 03:10:03 amand we have the schematics AFAIK

author: TERRA Operative
author_rank: Super Contributor
timestamp: February 22, 2025, 04:35:29 pm
content: Yup, schematics attached below for reference:

author: cosmo little
author_rank: Contributor
timestamp: February 26, 2025, 02:36:47 pm
content: Replaced all the electrolytics on the output side, and the 150uF,400V main smoothing. No change in behavior!I then ran the counter off 3 lab power supplies for +5V,+12V, and-12V. I did not connect the floating 9V supply as I could not find any connections to this on the schematic.It worked perfectly, powering up every time.This confirms that the power supply still has problems. I measured the noise on each supply, and found about 50mV PP on the 5V supply, and 100mVPP on the 12V supply.Attached oscilloscope trace of each supplyWith this amount of noise, counter does not power up. I intend to wait overnight and see if the noise decreases.

author: cosmo little
author_rank: Contributor
timestamp: February 26, 2025, 03:27:49 pm
content: Further to my last post, I measured the transient behavior of the power supply when the counter is switched on. This is horrible, its not surprising that the startup fails.There must be something wrong with the PSU regulation. I will replace remaining 3 electrolytics on the input side, and also some of the ceramic capacitors.The DC regulation seems to work fine

author: TERRA Operative
author_rank: Super Contributor
timestamp: February 26, 2025, 04:16:43 pm
content: Did you use low-ESR capacitors?What brand and model did you use?I have had a 53181A that didn't respond to replacement of electrolytics (although they were leaky so did need replacement), and after testing literally every component in the PSU as ok, I started replacing the ceramic capacitors in an act of desperation and the PSU started working but with bad regulation. After I replaced them all the PSU worked fine, so a number of them were somehow bad. I've never seen ceramic capacitors test ok but act failed in circuit, but there it was... Probably something weird when DC bias was applied in circuit or something.

author: madao
author_rank: Frequent Contributor
timestamp: July 13, 2025, 11:43:41 am
content: I have repair today PSU of HP 53132A (hiccuping )Preowner has replaced old caps by Panasonic FR/FS. It doesn't help.I have checked: Oh, R29B (330k) is open.all four 330k resistor replaced. PSU is well aged with browish pcb around primary switch FET.Now works PSU fine.Pay also attention on resistor with high value, which it should work with few hundred volts.