Power supply of xeon03 doesn't work #2
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It doesn't turn the OK LED.
Model is DPS-750XB A, REV: 05F
Here is the power supply picture:
The output is 0 V for the 12 V large pins, however the 3.3 V output is working.
After opening the case:
The filter close to the power connector seems like an after thought.
Damm, I accidentally must have damaged this diode(?), close to pin 45, I will need to re-solder it. It seems like it had a cold solder.
This 24C02WP Serial EEPROM seems a bit off:
This issue can be debugged further by checking at which point the power supply fails to deliver the proper voltage, but it will take some time. Provided that these power supplies are not very expensive (100-200 €) it seems a better option to order another as replacement. I ordered in petition:
https://webapps.bsc.es/resource-petitions/normal-petition/17545
In the meanwhile I can try to revive it.
Let's solder this Zener:
The pad is broken, but this seems to be a 5.1 V zener: https://www.newark.com/nexperia/pdz5-1b-115/zener-single-diode-5-1v-2-sod/dp/34R4470
assigned to @rarias
Ordered some replacement 5V1 SOT-323 Zener diodes.
Temporarily I moved the power supply from the oss01 node to xeon03, so we can use it for SLURM.
The 5V1 Zener diodes arrived from China.
mentioned in issue #8
The Z8 Zener in the board doesn't seem to be a 5.1 V but is more close to 5.6V, so a better replacement is W9. Here is a partial V-I trace of reverse current:
I try to do a full trace as soon as I manage to generate a suitable waveform.
In any case, is seems to be used as 5V over protection of the digital channel isolator (ADUM1410), so I don't think the value is critical.
Here is the approximate V-I curve of the original Z8 zener and the replacements I got W8 and W9 labeled 5V1 and 5V6 respectively.
The Z8 has a breakdown voltage of 5.1V and matches the W8 zener, however the reverse current curve in the W diodes is slower. The ADUM 1410 can withstand up to 7 V of supply voltage, so it should be okay to use any of the W8 or W9 diodes.
The power supply pinout is given in the board manual:
The RC community has used this power supply to charge batteries. In this post, after a crazy mod, the shorted pin marked with SGND is grounded to enable the power supply. This pin corresponds with the A21, named FM_PS_EN_PSU_N, which makes sense.
Replaced with W8.
I put it back together.
Lets see if it powers up or blows.
So far it starts and outputs 3.3V on some of the A19, A20, A21 pins, but nothing on the +12V. The A25 PWROK is 0V, so it seems to be not OK.
To debug it further I will need to start poking at the 12 V power rail upstream and see if the main coil is being switched. I will also need to do some reverse engineering of the bad ass digital control board, which contains some PIC controllers, and see if they give me some clue of the problem (there may be a serial port exposed). But for that I will need an isolation transformer to avoid blowing the scope, as that part of the circuit is not isolated from the AC line.
Additionally I will need a way to power it while keeping the PCB exposed (probably it requires the fan to be plugged in too). Maybe I can solder some test wires to the interesting pins, but this will not be free of hazard. Specially if I cannot plug it to a properly grounded outlet.
Estimated time of arrival of replacement power supply is May 8-12.
Arrived to helpdesk.
I connected the new power supply to the oss01 machine, but it doesn't boot. The BIOS produces the code 1-5-4-2, which is emitted when there is a problem with the power supply.
The problem with the power supply was caused by the short circuit in the oss01 node. There has been no evidence yet that the power supply is bad.