Indigo 2 Impact PSU dead, diagnosis & advice

[stormy]

Hi people,

I'm attempting to diagnose a Zytec 22943507 Rev C for Impact Indigo 2 systems.

PSU details:


Description of fault:
Absolutely no output when power applied. Connecting 'run' pin 11 to 'standby 5v' pin 5 does not start the PSU. No output on pin 5 'standby 5v' at all.

Some things already done: Replaced most of the capacitors on both HV and LV sides, as suggested on Ian Maplesons guide. The only caps not replaced yet are the super-large two on the HV side and the 6800uf caps. I have also re-soldered most points on the boards that get hot, to make sure the solder is good. None of this helped.

In-depth testing:

I do not have an impact graphics terminator, it wasn't attached to my PSU like others, so I had to make one from scratch:


I measured which side was GND and plugged the sense cable in for black to GND yellow to 3.5v.

Another thing I was interested in was the initial AC filter. I tested the continuity and it all seemed fine. I opened it up and took a picture just for the record:

 

[stormy]

I want to measure the connectors that go from HV > LV boards. So I plugged my load resistors in to pins 15 & 16 (5v & GND) on the left connector, then pins 13 & 15 (12v & GND) on the right connector. My 5v load resistor is 2R2K and my 12v is 10R. I also connected a hard disk to the Molex for extra load & connected my home made graphics cable terminator.

These are the measure points, I put arrows on the PCB where the connector points are:


Here is a photo of the HV side:

Here is a photo of the LV side:


Photos of my load setup:


Photo of the PCB dismantled for taking the measurements:

Of course I have checked the fuses, and just for the record here are some resistors on the HV side that get hot (and show by the PCB discoloration:


Result of testing so far:

Absolutely nothing on the output of the HV>LV connectors. But I did notice those resistors are getting hot on the HV side still.

 

[stormy]

Any suggestions on my next steps appreciated. I assume the problem must be on the HV side after these tests? Thanks.
ps - Cheers for all your details about these psu's on the forum @Elf

 

[stormy]

I am thinking it may be worth replacing the AVS1AC (datasheet attached)
There are also 2x MOC 8101 optocouplers I am thinking of replacing (datasheet attached)

Thoughts?

 

[Elf]

No problem! The discoloration does seem slightly abnormal at least from the ones I have taken apart, and as far as I can recall. Unfortunately I don't have too much concrete advice to offer in terms of how to fix these, but it may help to start looking at the supply and drawing out a topology from it, which would aid in troubleshooting and seeing what piece might be malfunctioning.

 

[weblacky]

Well, I have a thermal imager, so I cheat. Normally I used a 300W current limiting light bulb setup for draw indication. Usually you either have a non-starting, constantly restarting (pulsing bulb), or a start followed by a protection mechanism engaging.

I use a thermal imager to stare (briefly) at the PSU PCBs while powered, shows shorted Diodes and FETs very well. If it's a resistor issue, that's very different. If you want to troubleshoot a resistor issue, desolder one-end of each resistor and recheck its value against markings, replace if out of spec.

I do not normally testing PSUs powered (I have a lot of power-off testing gear), but assuming you have a current limiting setup made from a light bulb with enough wattage to allow normal startup, it's great way of doing a cheap voltage injection-style hunting.

 

[stormy]

Update, I am getting 7.7v AC and 5v AC from the double thick wires going from HV to LV.