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| Loud "chirping" sound coming from HP3456A voltmeter (repaired) |
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| pqass:
--- Quote from: intabits on November 12, 2022, 02:11:52 pm ---Thanks for the ideas. A snap-in would be simple, but a quick search of the local suppliers shows nothing suitable. And I don't fancy my chances of finding a 5 pin job even with the main online suppliers. I think the multi-caps on a PCB is a really neat solution, I'll probably go with that. There's a couple of similar caps in the 3455s, so possibly some economy of scale in the PCB design process. --- End quote --- Barbouri has shared it here https://oshpark.com/shared_projects/EVFWnnBD. I think you get three copies for the price. --- Quote ---Also, subject to available space, a long PCB with multi-caps might do for the large axial cap A3C6. --- End quote --- Well, at least this cap is still available https://www.digikey.ca/en/products/detail/vishay-sprague/53D183G025JT6/5611315 if you can stand the price. |
| pqass:
--- Quote from: intabits on November 12, 2022, 02:19:04 pm --- --- Quote from: pqass on November 12, 2022, 12:34:41 pm ---Also, the MOSTEK ROMs have been known to die of old age. --- End quote --- I knew of that, but thought I'd just deal with it if/when it happened. But thinking about it some more, I should remove, socket, read and burn replacements. Just to be sure, and in case my ROMs are different to the online images... And again, subject to space available, using adapter PCBs --- End quote --- I'm in the planning stage of fixing my own 3456. I'm going to start with sockets first too. I certainly don't want a rats nest like this https://xdevs.com/fix/hp3456a/. I think the simplest solution is just to make an adapter PCB per ROM for a 2764 as described here https://bama.edebris.com/manuals/hp/3456a/. You could consolidate into one [E]EPROM but that would require you to find A13, A14, and replace/interface with the 74LS138 (U6). Too much thinking (risk?) involved. |
| srb1954:
--- Quote from: intabits on November 12, 2022, 02:11:52 pm ---Thanks for the ideas. A snap-in would be simple, but a quick search of the local suppliers shows nothing suitable. And I don't fancy my chances of finding a 5 pin job even with the main online suppliers. I think the multi-caps on a PCB is a really neat solution, I'll probably go with that. There's a couple of similar caps in the 3455s, so possibly some economy of scale in the PCB design process. Also, subject to available space, a long PCB with multi-caps might do for the large axial cap A3C6. --- End quote --- I used an EPCOS B41231-B7478-M part which is a 4700u 35V part, not a 63V part as I incorrectly stated earlier. It is a 2-pin snap-in cap with 10mm pin spacing that fitted OK into the existing PCB hole pattern after rotating it about 45deg. In the normal course of events I would have used a modern 4700u 16V radial lead cap, which should have been a adequate replacement for the old 4000u 15V Sprague part. However, I measured the ripple current in circuit and decided to go for a larger cap to provide some ripple current derating and a longer capacitor life. The larger snap-in cap has about double the ripple current rating compared to a standard 4700u 16V radial leaded part. |
| dietert1:
Here we have four of those original Sprague caps 4000uF/15VDC. The LCR meter says C /uF ESR /Ohm DC 4300 0.048 8734 3710 0.057 8647 3120 0.31 8908 4510 0.076 8713 We used 10000uF/16V caps to replace them. The ones that failed more often are the smaller caps in the voltage doublers. One can add two diodes to prevent reverse voltage during power-up. Regards, Dieter |
| intabits:
--- Quote from: pqass on November 12, 2022, 03:30:01 pm ---Well, at least this cap is still available https://www.digikey.ca/en/products/detail/vishay-sprague/53D183G025JT6/5611315 if you can stand the price. --- End quote --- I don't know how I missed that, I was looking mostly at local suppliers, but did also look at digikey. That is the most elegant solution, but comes out to about $45 pacific pesos, and I have 2 to replace, so a bit steep. Especially as the original parts may be just fine. I'll test them, and if dodgy, decide which way to go. I'll do my own home made PCB(s). A little trickier being single sided, but certainly doable. On the "ROM Rat's Nest", yes, I would aim for something neater than that... --- Quote from: srb1954 on November 13, 2022, 03:30:46 am ---I used an EPCOS B41231-B7478-M part which is a 4700u 35V part, ...not a 63V part as I incorrectly stated earlier. It is a 2-pin snap-in cap with 10mm pin spacing that fitted OK into the existing PCB hole pattern after rotating it about 45deg. In the normal course of events I would have used a modern 4700u 16V radial lead cap, which should have been a adequate replacement for the old 4000u 15V Sprague part. However, I measured the ripple current in circuit and decided to go for a larger cap to provide some ripple current derating and a longer capacitor life. The larger snap-in cap has about double the ripple current rating compared to a standard 4700u 16V radial leaded part. --- End quote --- Hmmm, that's a simpler solution, and at $3.43, the price is right! --- Quote from: dietert1 on November 13, 2022, 08:46:49 am ---We used 10000uF/16V caps to replace them. The ones that failed more often are the smaller caps in the voltage doublers. One can add two diodes to prevent reverse voltage during power-up. --- End quote --- Not sure exactly what you mean there, but I'll work it out. Sounds like it's worth doing, thanks for the Tip! |
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