So what is the "Panasonic power supply issue"?

[starbond]

Ed, I built the dim bulb tester, and now Im ready to test voltages. Am I looking at the DC side voltages? Will i know when one looks off without having reference voltages?

[Ed in Tx]

The bulb test was to verify the short was gone before you plugged it in directly to AC. if you didn't do that you might have damaged the new Q4. Have you rechecked it? Also I'm a little old fashioned when testing diodes and transistors. I just use an analog volt-ohm meter usually set on 100X scale and test for a shorted condition. If a diode conducts one way and not the other it's generally good. Also not advised to go probing around in a power supply like that since the primary side is hot to ground. You need an isolation transformer to do that but rarely necessary to be working on that area of the PS powered on. There should be 5V and 12V outputs at least once it's running with a dim bulb. Not sure where else to go from here without a schematic.

[starbond]

Thanks Ed, I agree without a schematic is difficult. I think Q4 may indeed be damaged again. Pulled it out, bulb still lights very bright with it out, so guessing the problem is still elsewhere

[Ed in Tx]

Did you check D1 the full wave rectifier for a short?

[starbond]

Ed, D1 is a S1VB20 or so, tested in diode mode across all pins as show in data sheet and got .6V forward and overload OL in reverse

[Ed in Tx]

So you went 1 to 2, 1 to 3, 2 to 4, and 3 to 4 and all tested like a good diode? Then it's something else...

[starbond]

Originally Posted by Ed in Tx

So you went 1 to 2, 1 to 3, 2 to 4, and 3 to 4 and all tested like a good diode? Then it's something else...

Yes all good.
Ive tested all the diodes in the HOT zone, all the transistors bar Q4, replaced a few capacitors that I had on hand. I must be missing something or measured something wrong.
When I measure DC voltages past the rectifer I only get about .5V
When i measure AC votages at the mains I'm only getting 1-2V coming in from the hot and neutral pins

I'm close to giving up on this and taking a loss. which is a shame because otherwise the VCR looks barely used.

[damen]

Have you mentioned the model number ? Someone here may have a diagram.

[Blast]

Ed in Tx is ALL OVER this one. To both paraphrase him and add to what he said: You will need to find EVERY COMPONENT that is bad, or near-bad (read: resistors), before these power supplies will fully function and not take out most, if not ALL, of the components you've already replaced! Trust me! That's both on the "hot" side AND the secondary.

These pre-'86 Panasonic SMPS's were nothing but a nightmare for me as I was learning VCR repair in the late 80's. I got my ass kicked on several occasions. Fortunately, the senior tech (read: boss) was there to bail me out. Most of the time...

It wasn't until Panasonic's '85-'86 models where the power supply circuitry was finally 'trimmed down a bit' to my limited brain power before I would really start to get my wings on these. Then, in the late 80's I would develop a list of EVERYTHING that should be replaced before further diagnosing any ADDITIONAL problems.

Good luck, starbond, on your journey repairing this and ultimately playing back your tape collection!

Brian

[vortalexfan]

Originally Posted by starbond

Its possible, but hopefully not.

Q4 arrived today, put it in the circuit and it STILL blows.
I tested diodes 1-5 on the circuit as well as Q1 and q2 which appeared to be still in spec
D1 is a bridge rectifier so its probably fine
D2 reads .5V forwards and OL reverse
D3 reads .6V forwards and 2V reverse
D4 reads .6V forwards and 2V reverse
D5 reads .6V forwards and 1.8V reverse
these were tested in circuit as the leads are so short, if i removed them i dont think id be able to get it back in.

D3-D5 on your VCR appear to be bad, because on diodes they're only supposed to measure voltage one direction, and you're measuring voltage (albeit a very small amount) in both directions, which tells me that D3-D5 might be part of your problem (and possibly something for me to check on my VCR as well.)

[starbond]

Originally Posted by Blast

Ed in Tx is ALL OVER this one. To both paraphrase him and add to what he said: You will need to find EVERY COMPONENT that is bad, or near-bad (read: resistors), before these power supplies will fully function and not take out most, if not ALL, of the components you've already replaced! Trust me! That's both on the "hot" side AND the secondary.

These pre-'86 Panasonic SMPS's were nothing but a nightmare for me as I was learning VCR repair in the late 80's. I got my ass kicked on several occasions. Fortunately, the senior tech (read: boss) was there to bail me out. Most of the time...

It wasn't until Panasonic's '85-'86 models where the power supply circuitry was finally 'trimmed down a bit' to my limited brain power before I would really start to get my wings on these. Then, in the late 80's I would develop a list of EVERYTHING that should be replaced before further diagnosing any ADDITIONAL problems.

Good luck, starbond, on your journey repairing this and ultimately playing back your tape collection!

Brian

Oh boy, maybe I'm biting off more than I can chew haha. I wouldve hoped the primary side was the issue as I have only been focused there BUT maybe there's something obvious on the secondary side I have missed.
I'm no electronics pro, but this is the first time I've dealt with a bad power supply, in my limited years of working on VCRs, tape decks, receivers, etc.
It will be rewarding to get it working again, if not to see all the lights go on and putting a tape in and seeing the wondeful picture. Now if it turns out there's also a tape transport problem, well....

I want to thank all of you and Ed in particular for the help so far. I can give values and pull parts and replace them but where i struggle is intpresting what the values mean, and how to trace the board to the issue as I have no EE experience beyond self experimentation and all the folks at AK and VK

Vortex,
I admit i have no knowledge of diodes beyond that its kind of a one-way power direction-er, but I have seen conflicting information that varies from "it should be OL in reverse" to "getting a reverse measurement is OK"
Now that being said, these diodes are small and only have a colored band around them if anything, is there an easy way to identify how it should be replaced without a schematic?


Lastly, when I removed the bridge rectifier and turned the power on, there was no fuse blowing. Probably doesnt mean much but its the only time a pulled component prevented a blow (this was pre dim-bulb)

[Blast]

What is the model number?

[vortalexfan]

Originally Posted by starbond

Oh boy, maybe I'm biting off more than I can chew haha. I wouldve hoped the primary side was the issue as I have only been focused there BUT maybe there's something obvious on the secondary side I have missed.
I'm no electronics pro, but this is the first time I've dealt with a bad power supply, in my limited years of working on VCRs, tape decks, receivers, etc.
It will be rewarding to get it working again, if not to see all the lights go on and putting a tape in and seeing the wondeful picture. Now if it turns out there's also a tape transport problem, well....

I want to thank all of you and Ed in particular for the help so far. I can give values and pull parts and replace them but where i struggle is intpresting what the values mean, and how to trace the board to the issue as I have no EE experience beyond self experimentation and all the folks at AK and VK

Vortex,
I admit i have no knowledge of diodes beyond that its kind of a one-way power direction-er, but I have seen conflicting information that varies from "it should be OL in reverse" to "getting a reverse measurement is OK"
Now that being said, these diodes are small and only have a colored band around them if anything, is there an easy way to identify how it should be replaced without a schematic?


Lastly, when I removed the bridge rectifier and turned the power on, there was no fuse blowing. Probably doesnt mean much but its the only time a pulled component prevented a blow (this was pre dim-bulb)

The band side of the diode is the cathode side (if I remember right) and that's the side that the voltage goes into and is supposed to have no voltage on, the non-banded side is the anode and that's the side the voltage comes out of and is supposed to have voltage on.

I hope that helps, and if I have the terms mixed up, feel free to correct me.

[starbond]

Originally Posted by Blast

What is the model number?

Panasonic PV-1430 with a mfg date of 1984. I think any of of the sister models might have a similar layout assuming they were made around the same time (PV-1530, 1630, 1730)

Vortex,
Indeed that is how you tell which end of the diode is which, but how do I know what to replace the current diode with? there are no numbering or indications on the component to a part# so I can buy a replacement.

[vortalexfan]

Originally Posted by starbond

Panasonic PV-1430 with a mfg date of 1984. I think any of of the sister models might have a similar layout assuming they were made around the same time (PV-1530, 1630, 1730)

Vortex,
Indeed that is how you tell which end of the diode is which, but how do I know what to replace the current diode with? there are no numbering or indications on the component to a part# so I can buy a replacement.

Looking at the pictures, the diodes do actually have a number on them. Remove the diodes from the VCR and you will see a number on there, it will look like 1Nxxxx or something similar.