Electronics > Repair

Agilent 53132A Counter Repair (FIXED and Upgraded)

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TheSteve:
We shall see what the problem is. The front ends are totally fine. It looks to be something just after that. I may be buying a parts board in the future! The whole thing was $165.00 so I have a budget for parts.

soul40k:
 
--- Quote from: TheSteve on February 04, 2016, 06:45:27 pm ---We shall see what the problem is. The front ends are totally fine. It looks to be something just after that. I may be buying a parts board in the future! The whole thing was $165.00 so I have a budget for parts.

--- End quote ---

That is where I sit right now, the front looks fine, really weird actions with just a completely spastic display with nothing connected, but I touch it when live, on the bottom, and it stops. This is going to be the death of me, probably something really simple that I am just missing.

HighVoltage:
Can you show us in the schematic where you have to touch to make the display stable?

TheSteve:
Spent some time last night working on my 53132A. The entire time I just kept hearing Shahriar in my head saying "Follow the signal path" lol.

Anyway, some progress was made and I know I'm close. While following the signal flow between the front end and the FPGA I kept getting that feeling something obvious was wrong yet I couldn't see it. I briefly thought maybe the FPGA was bad as it was not generating any reset signals but then it occurred to me that it probably had to detect some sort of signal before it would reset the count circuitry. This proved to be true as selecting input two and then going back to input one would generate 2 or 3 reset pulses that could be traced through the logic.  At this point I looked at why I was getting no LED indication showing the selected input or gate samples. So I focused on U50. I had previously gone through all of the logic chips and verified +5, -5 and ground but I thought I'd do it again on U50. The -5 was nice and steady on my 34461A but the +5 was only steady for the first 3 digits. A quick hit with the soldering iron solved that problem and I now had input and gate indications. I still received the failed front end and failed measure errors at boot but it correctly measured the frequency being input which it had never done before. I should also mention at this point I had removed U44 which is a buffer opamp to set the trigger levels as it just didn't look right comparing its in and out voltages. I gave channel 1 a fixed trigger level with a resistor. After seeing it count the frequency properly I reinstalled the original U44. At this point it will not count anything at all and still gives the same errors. I get the feeling I am now at the point of the original failure which started the previous owner resoldering everything. The bad solder connection on U50 was caused by the previous rework as nearly all of the logic chips in the front end have been removed and resoldered(maybe replaced, I'll never know). It was late so  I had to pack it in for the evening. I will take a very close look at U44 tonight though. Unless I can say 100% for certain it is good I will order a replacement from Digikey, it's in stock for 5 to 6 bucks and may be all that is really wrong with the unit. I know it can count a frequency correctly so there there can't be much else wrong right?

btw, the previous person that did the rework has some skill but not really enough to do a proper job. The soldering they did is far from excellent and they removed a part or two that there was clearly no need to remove as they can easily be verified 100% good in circuit. They also left the signature amateur calling card in the top of one of the relays in the form of soldering iron melt marks.

soul40k:

--- Quote from: HighVoltage on February 05, 2016, 08:13:11 am ---Can you show us in the schematic where you have to touch to make the display stable?

--- End quote ---

It is literally anywhere near the front end, no specific point, I got busy with another job,  so I haven't tried other places yet, have to get back to it soon though.

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