Magnavox 30MF200V/17 Won't Power Up

[tom66]

Re: Magnavox 30MF200V/17 Won't Power Up

Is there a detailed schematic available?

[kevinm34232]

Re: Magnavox 30MF200V/17 Won't Power Up

Yep you have it

[tom66]

Re: Magnavox 30MF200V/17 Won't Power Up

Great... Resistor 3544, and capacitor 2544 join at one point. At their mid point please measure the voltage there. If less than 5V, indicates a fault which will cut the relay out.

[kevinm34232]

Re: Magnavox 30MF200V/17 Won't Power Up

Got 5.3V there

[tom66]

Re: Magnavox 30MF200V/17 Won't Power Up

OK, now between 3560 and 3561. Should be around 0.7V there, possibly a little more.

[kevinm34232]

Re: Magnavox 30MF200V/17 Won't Power Up

Do you mean 7560 and 3561? If so, 0.73V.

[tom66]

Re: Magnavox 30MF200V/17 Won't Power Up

7560 and 3560 are meeting at the same node so that's fine.
OK, now check pin #1 of 1305.

[kevinm34232]

Re: Magnavox 30MF200V/17 Won't Power Up

Thats 5-5.2V

[kevinm34232]

Re: Magnavox 30MF200V/17 Won't Power Up

What pages are you on so I can follow you?

[tom66]

Re: Magnavox 30MF200V/17 Won't Power Up

Did you hold those previous readings through power up and relay click off to see if they change? From those readings, the relay should stay on. So either the relay is faulty (rare), there is a loose/weak connector/solder joint (vaguely plausible) or something else is wrong (not sure what.)

[kevinm34232]

Re: Magnavox 30MF200V/17 Won't Power Up

Yes those last readings you asked for all are steady until click off and pin 1 of 1305 is around 5.3v until click off then hangs at just under 5v.

What about the 400V line in the schematic that is around 315V is that low? Am I missing something further upstream?

[tom66]

Re: Magnavox 30MF200V/17 Won't Power Up

But you DO see a drop in voltages at the moment of the click?

[kevinm34232]

Re: Magnavox 30MF200V/17 Won't Power Up

Really only after the click

[tom66]

Re: Magnavox 30MF200V/17 Won't Power Up

The click can only occur if one of those voltages drops so it will occur momentarily before the click. I have had a power-down fault like this before. It's not easy to track down without a 2 channel digital scope: with just a DMM, you're left wondering if the voltage dropped out because the SMPS shut off or the SMPS dropped out because the voltage dropped out. You could be talking about a few hundred milliseconds between the events.

[kevinm34232]

Re: Magnavox 30MF200V/17 Won't Power Up

I see. If you had to guess would it be the main PS board or the standby board? It's time I get a nice scope I think..

[tom66]

Re: Magnavox 30MF200V/17 Won't Power Up

I would be focusing on the standby PS, on part of that shutdown circuit.
Rigol DS1052/DS1102E is a good scope for around $300.

[kevinm34232]

Re: Magnavox 30MF200V/17 Won't Power Up

I can try getting that board (not too expensive), but I'm concerned with the 400V line being around only 315V, is that something that could cause it to shut down too?

[tom66]

Re: Magnavox 30MF200V/17 Won't Power Up

Is that line 160/170V in standby?

[kevinm34232]

Re: Magnavox 30MF200V/17 Won't Power Up

Its 85V in standby

[budm]

Re: Magnavox 30MF200V/17 Won't Power Up

Wow, 85VDC right at the filter cap's legs?