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Agilent 54835A scope (4 channel 1GHz / 4Gs/s) repair & uphack

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nctnico:
Perhaps some electrolytic capacitors turned bad.

analogRF:

--- Quote from: nctnico on October 26, 2019, 05:41:40 pm ---Perhaps some electrolytic capacitors turned bad.

--- End quote ---

That was also my suspicion but where...it's been sitting on the corner for 2 or 3 month only. caps on the motherboard at least look ok ...PSU voltages are all good too...

Converter:
The most perishable product is aluminum capacitors with liquid electrolyte. Check the voltages stability from the power supply using a different oscilloscope in roll mode. Make sure that the ripple is normal. Some contacts may also oxidize, especially if you store it in a humid environment. Check connectors.
Check if a forced shutdown signal is received from the oscilloscope control circuit, or the protection in the power supply unit is activated against overcurrent, temperature, or a signal from the supervisor for voltage.

Jwalling:

--- Quote ---what do you think could be wrong? I have been dicking around with reseating PCI and ISA cards and RAM sticks but it keeps rebooting randomly. I don't think it is heat related because sometimes it happens right after cold boot before even win98 starts.
--- End quote ---

Try running memtest86+ on it.

analogRF:
First of all my own 54845A which was randomly rebooting seems to be working fine again...I ran memtst86 for an hour and it didn't find any error. I had cleaned up all the board edges, connectors, etc...and I checked all the main filter capacitors on the PSU and on the mobo and they were all very good even better than the brand new ones I was going to replaced them with! (they were very good both in terms of ESR and value)
but after playing with it for a couple of days and keeping it running eventually the reboot problem went away and it has been working 1-2 hours at time for a while now. Maybe there is a bad cap somewhere that was about to die when the unit was stored for a couple of month and now that it has seen voltage across it, it has come back to life (and it will probably die again) but I don't know where that could be...I suspect one of the caps in the PSU but not in  the output filters, perhaps on that control daughter board which is soldered on to the main PSU board...

However, I am now dealing with another 54845A which is not mine. Belongs to a colleague who is not into repairing stuff although he does a lot of electronics specially RF...This is a VIN 033 model made around 2000 with FIC VA-503A motherboard (newer than mine) with one stick of 64MB SRAM and K6/400 CPU. Based on his description the unit had been working until the day that it was put aside about 5-6 month ago and now it does not boot. It stops at "Verifying DMI pool data ...." and nothing after that. Recognizes the HDD and I have checked the HDD outside the unit with chkdsk /r and no errors. I also connected the original HDD of my own older unit to it just to see if it boots.
There were tons of leaky bulged elcos on the motherboard which I replaced them all (all the 1000uF and the three 220uF and only 2 of the many 10uF but not all of them. The 10uF caps are not bulged or anything) but nothing changed...I tried to boot it with only the HDD, interface board and the video board and still a no go....tried different SRAM sticks...

any idea what else I should be looking for? All voltages on PSU are accurate and I have cleaned all the connectors...changed cmos battery and played with cmos many times...tried to boot it froma DOS floppy in the LS120 zip drive but still the same issue...

I am out of ideas now.... :-// :palm:

EDIT: any help is appreciated. I know there are people on this thread that have worked on these infinium series a lot more

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