K7500 power supply issues

gobsgraham

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Mar 26, 2009
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Alright. I have tried to fix this board a few times and always give up. I am still a newbie so I want to go back to basics. I have pretty good troubleshooting skills so I am going to scrap everything and start at AC in until I find it. That is where I need help.

Can I just plug in AC and work on this on my bench or do I need to have it plugged into the monitor. It is hard to get voltage readings and stuff when it is in my cab so I just want to turn it on sitting on the bench with nothing but AC connected. Is this going to fry anything or arc and spark if the anode plug/cup is not plugged into anything?

Second, I think I should isolate the power supply section and am sure I can figure it out on the schematic but if someone could quickly tell me which resistor to open that would be great as it would save me some time.

Thanks for your help and I will try and update this although it will be slow as I don't have a lot of time to work on this.
 
I suppose some history on the board would be helpful aswell but I was just going to start at point 0 and work my way in.

I bought the board dead. R106 was blown to pieces and T101 was likely dead too. I replaced both of them from a donor board and it still wouldn't fire up.

Last night I was working on it and found a bunch of bad caps that I replaced. I also found that Q101 was blown completely in half. I replaced it but still no go. I'm getting a bunch of weird voltage ratings and it seems that everything has -39VDC on it which is just wrong.
 
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