1987 GE 3 Head Hi-Fi Stereo VCR Acquired Today

[vortalexfan]

Originally Posted by probnot

Hmm that sounds shorted. On the diode setting, the two ~(AC) pins should measure open (both directions).

For the DC side (+ and -) you should see close to 1.0v but only in one direction.

That's what I thought. There's a number on the bridge rectifier, I think I might have something in my parts stash that might work, (I had found a couple of baskets at the local SA a couple of years ago that were full of NOS TV and VCR parts like IC chips, capacitors, resistors, diodes, fuses, rectifiers, rectifier bridges etc. that came from a local appliance store that went out of business.)

[vortalexfan]

The Bridge Rectifier in my VCR that was bad is a S1WB S40 Rectifier Bridge, at least that's the numbers on the top of the rectifier bridge which when I look that number up on google, nothing shows up...

See picture below.

[old_tv_nut]

40 71 could be just a date code for 40th week of 1971, if that fits the date of manufacture of the VCR.
Edit: although that seems very early.

[vortalexfan]

Originally Posted by old_tv_nut

40 71 could be just a date code for 40th week of 1971, if that fits the date of manufacture of the VCR.
Edit: although that seems very early.

That seems a bit too early for a date code, unless Panasonic was using up old parts when making their VCRs, because this VCR is from 1987...

[old_tv_nut]

Originally Posted by vortalexfan

That seems a bit too early for a date code, unless Panasonic was using up old parts when making their VCRs, because this VCR is from 1987...

Yeah, on second thought, not likely.

[jr_tech]

Originally Posted by vortalexfan

That seems a bit too early for a date code, unless Panasonic was using up old parts when making their VCRs, because this VCR is from 1987...

If it follows the numbering scheme used on this example, the last two digits are a date code (perhaps the first month of 1987 ?)

https://www.mouser.com/datasheet/2/3...BA-1202965.pdf

Perhaps the 40 indicates 400 volt?

just a WAG,
jr

[vortalexfan]

Originally Posted by jr_tech

If it follows the numbering scheme used on this example, the last two digits are a date code (perhaps the first month of 1987 ?)

https://www.mouser.com/datasheet/2/3...BA-1202965.pdf

Perhaps the 40 indicates 400 volt?

just a WAG,
jr

Well I ordered some diodes from mouser that had similar specs to the original rectifier bridge (which I did find a spec sheet for an S40 type S1WB rectifier bridge), so we'll see what happens when it gets here, I had also replaced one of the main filter caps (the 4.7 uF 200 VDC filter cap) that tested bad (had extremely high ESR value of 15k ohms.)

[vortalexfan]

UPDATE: Replaced the bridge rectifier and the VCR is still blowing fuses, so I wonder if maybe the Q1 is bad in the power supply board (the transistor on the heatsink.) when I did the diode test it seemed like it checked fine, but maybe I wasn't doing the check correctly.

What would the correct replacement for that transistor be? I looked up that transistor (it was a Panasonic part number) and it didn't seem to cross-reference to anything currently being made (no NTE parts or anything.)

[starbond]

If its anything like my unit, the heatsink transistor was bad after the fuse kept blowing. my mistake was not using a dim bulb tester the first time around, so I had to buy the replacement transistor TWICE. Luckily there was some NOS on ebay.
Yours has no C or B value on it?

[vortalexfan]

Originally Posted by starbond

If its anything like my unit, the heatsink transistor was bad after the fuse kept blowing. my mistake was not using a dim bulb tester the first time around, so I had to buy the replacement transistor TWICE. Luckily there was some NOS on ebay.
Yours has no C or B value on it?

I'm guessing you're right that that heat sunk transistor is bad on my VCR, it did have a code on it, but I can't remember what it was now, and I made the mistake of putting the power supply back into the VCR.

I'll take a look in the morning.

[djfivos]

Hello. That looks like a rebadged Panasonic PV-4750. The 4760 is the hi-fi stereo version. Be sure to check the electrolytic caps in the power supply before using the machine.

[djfivos]

If this is the power supply your machine has, I can post the full schematic if you need it.

Fivos

[vortalexfan]

Originally Posted by djfivos

If this is the power supply your machine has, I can post the full schematic if you need it.

Fivos

yep that's it right there, I still need to check the switching transistor in the power supply (Q1) because this power supply only has 2 transistors in it overall and the one of them is the Switching Transistor (the transistor attached to the heatsink) that's the only part I haven't changed yet that I suspect might be still causing the VCR to blow fuses.

[djfivos]

Originally Posted by vortalexfan

yep that's it right there, I still need to check the switching transistor in the power supply (Q1) because this power supply only has 2 transistors in it overall and the one of them is the Switching Transistor (the transistor attached to the heatsink) that's the only part I haven't changed yet that I suspect might be still causing the VCR to blow fuses.

Did you disconnect Q1 from the circuit and measure it? Are the zener diodes OK?

[vortalexfan]

Originally Posted by djfivos

Did you disconnect Q1 from the circuit and measure it? Are the zener diodes OK?

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.