1987 GE 3 Head Hi-Fi Stereo VCR Acquired Today

[djfivos]

Originally Posted by vortalexfan

Yes, all the diodes checked fine yet. The only diodes that checked bad was the bridge rectifier, which I already changed that out for a modern replacement the switching transistor I have not had a chance to check yet, the way they did the power supply in this VCR is that you have to disconnect a ribbon cable that's connected in a strange manner and then undo 2 solder blobs holding it to the main circuit board and then bend a retaining tab and then gently remove it from the main board without cracking the main board.

Yes I've seen the process of removing the power supply in these machines. What I'm thinking is perphaps the caps in the primary side failed and caused the oscillator to go into a runaway condition and that caused the output voltages to rise up way too high to the point where the crowbar shorted and took out the switching transistor and other critical components. I've heard this can happen with Panasonics of this era.

[vortalexfan]

Originally Posted by djfivos

Yes I've seen the process of removing the power supply in these machines. What I'm thinking is perphaps the caps in the primary side failed and caused the oscillator to go into a runaway condition and that caused the output voltages to rise up way too high to the point where the crowbar shorted and took out the switching transistor and other critical components. I've heard this can happen with Panasonics of this era.

Yes, I'm pretty sure that's what happened as quite a few caps had puked their guts onto the board which had unfortunately damaged some of the traces, I checked the dioded including the zeners and they all checked as they should thankfully, like I said the only diode that seemed to of failed was the bridge rectifier.

[djfivos]

Originally Posted by vortalexfan

Yes, I'm pretty sure that's what happened as quite a few caps had puked their guts onto the board which had unfortunately damaged some of the traces, I checked the dioded including the zeners and they all checked as they should thankfully, like I said the only diode that seemed to of failed was the bridge rectifier.

What about the circuit protector PR1 (ICP-F38) in the secondary side across the 5 volt rail? Does it also measure bad (open)?

[vortalexfan]

OK, so I finally got around to taking the transistor out of my VCR, and it seems its a "proprietary" transistor (it was a transistor that was made by Matsushita themselves and it doesn't seem to have a cross reference to any currently made transistors, at least not that I could see.)

Does anyone know what a 2SC3870 NPN Triple Diffusion Planar Transistor cross-reference to?

[vortalexfan]

I figured it out. I had a transistor from a junker VCR and its working now.