150 VDC Power Supply T/S issues

[Darylbnet]

Hello All, We are trying to repair some old 120-150vdc power supply cards...

The problem is we can get the cards to work, but have an issue of spiking...
When at zero pot, the unit will stay at zero output, but will spike periodically, like every 30 seconds, some a minute or two, between each spike...
When we range the control pot up it will spike more rapidly till approx. 30-40vdc, and will smooth out for normal
firing and constant control up to approx. 120 vdc and stay steady...

We can see the firing network, slowly building voltage, till it saturates and causes the spike...

We only have one good board at this time, which works correctly, and doesn't spike, and ranges smoothly, when the pot is increased, to fire at 0vdc through to about 100vdc or 120vdc...

I will be posting any reference info I have to aid in this discussion...

We think it is a faulty capacitor, allowing this to build and spike, but any assistance of what areas to focus on would be GREATLY appreciated...
Will post more pics as I get them edited...
Tks...

 

[Alec_t]

We seem to be missing some of the schematic. What connects as inputs/outputs to all those terminals?
Where does the pot connect?
I see various test points 'TP'. Do you have info as to what voltages/waveforms should be present at each?
Are all the TP values what they should be?
At which point are you measuring the spikes?

 

[kellys_eye]

Given the age and the heat that the board looks to have suffered I'd be changing ALL the electrolytic capacitors!

 

[Alec_t]

It's possible the grime on the board is providing an unwanted leakage current path to account for the board misbehaving.

 

[Darylbnet]

Noted comments Thanks Alec and K., Sorry for the delayed response, I was on time off and the past 3 days back,
I have been non-stop on other projects...
I will pull what info I have on the TP voltages and where that control pot regulates it, and post them for you...

 

[Bluejets]

By the look of the board, pot could be crappy also, along with the multi connector.