Wednesday, June 17, 2015

Replaced ten tantalum capacitors, 100+ to go in the Pertec disk drive, plus fighting the Ztex/Xilinx toolchains and designs


When I brought the main logic board in to check, I spotted an exploded tantalum capacitor right at the top of the board. That made my decision for me - replace them all. I have 125 new tantalum capacitors coming in a few days from Digikey, which I will swap for ALL the accursed Mallory tantalums that are bombs waiting to go off.

My earlier order of a few replacement capacitors (and an op amp) will arrive today, so I can at least replace the known exploded component on the board and recheck resistances. I prioritized capacitors in the power supply regulation circuits, particularly those involved in the 'crowbar' circuits that force a short circuit to blow fuses if the voltage levels get too high, thereby protecting other components in the system.

This first round of changes has resolved the problem with the -20V raw supply fuse, but there is still something triggering the +10V raw supply crowbar. I began checking additional components on the board. I had a total of ten replacement capacitors on hand, so that is how many I replaced, one of the logic board and nine on the servo board surrounding the power regulation circuits.

I didn't get a chance to do a power-on test, due to the late hour when I finished, but that will be the way I check to see if I still have problems after this round of replaced capacitors. The challenge is that the crowbar circuit blows the +10V raw power fuse so quickly, I can't tell what might be wrong. My storage oscilloscope might be put to the test if I still have the problem tomorrow.


I did some initial trials to use alternate means of loading the flash on the ztex board so it will boot up when it receives power. However, so far it is not doing any better. I will keep trying different variations until I can make this work as intended.

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