Magnavox 42mf931d/37 no vset

[freakaftr8]

Hi all. I picked up another magnavox. I am fluent in this and it's brother Philips internals. I have rebuilt many ysus and buffers on this model series before. But this one is wierd and throwing me for a loop. It turns on black screen. Then white blotches of dots show up in sporadic areas. Anyway buffers test good and no shorts on the ymain. Off the power supply there is no vset. And vscan is about 17v low as well as ve is low too. Va and vs normal But no vset whatsoever. With ymain disconnected no voltages at all except vs and va which are at normal range I'm stumped. Disconnecting buffers does not change anything but I now cannot hear ysus making noise anymore. Buffers connected ysus ipm makes noise.
Your thoughts?

[freakaftr8]

Re: Magnavox 42mf931d/37 no vset

Btw with zsus disconnected ysus and buffers connected makes no change but I can hear ysus working. Only time ysus is quiet is when buffers are disconnected.

[freakaftr8]

Re: Magnavox 42mf931d/37 no vset

These voltages are interesting.

Vs 205 normal
Va 70 normal
Vscan -173 should be -190
Ve 63 should be 87
Vset -300mv essentially no voltage output.

If y main power disconnected I only have vs and va. Of course I believe this is normal due to logic board signal off causing power supply not to provide. I thought this series ps lj44-00092c still provided all voltages if ymain disconnected.

Oddly ve goes 0v when zmain disconnected. Guess it needs the load to startup voltages.
I'm stumped why all voltages besides va and vs are low with vset missing.

[freakaftr8]

Re: Magnavox 42mf931d/37 no vset

Now I'm almost positive the ysus and buffers are ok.

[freakaftr8]

Re: Magnavox 42mf931d/37 no vset

Well I got it up and running. It turned out to be a blown ic561 on the power supply. Also shorted zd565. I've seen this and had this problem before on another magnavox same model. The vscan is still not adjustable. It's stuck at -173v where it needs to be -190v. The varistor doesn't make a difference. I already swapped it pc565 (optocoupler) and still the same. If I remember I think on the last problem I had pc505 was bad its linked to shorted ic561.

[freakaftr8]

Re: Magnavox 42mf931d/37 no vset

Ok pc505 changed. Still no response from vscan varistor. Still sitting at-173vdc. I ohmed the varistor and its ok. What else besides a photo coupler and a varistor can cause the voltage to not be adjustable?