So what is the "Panasonic power supply issue"?

[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]

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

[starbond]

I measured the resistors on the high side, any I could find in numerical order, but couldnt find R7 anywhere. They all look okay, even R1 which is still within 5% so not likely to be a resistor issue. Visual inspection of all on the power board doesnt reveal any blackened or crisp ones.

[starbond]

Well i have some good news to share for once.
After getting my replacement Q4, the unit DOES power on now, although not fully.
When I flip the dim bulb switch the lightbulb lights for a second as the transformer starts and the vcr head whirs up for a moment, then the bulb goes out.
Once I press the power button the VCR then the bulb glows dimly the entire time the vcr is on. all of the front panel functions work excepct for part of the main screen VFD, the clock and time elements light but the orange PLAY FF RWD side does not. The whole thing runs weakly, I can put a tape in the transport and it will lower onto the spools and I can eject it, but Im guessing due to the bulb pulling current the unit is running not at full power.

I'm afraid to run the VCR without the bulb intermediary as I dont want to blow Q4 AGAIN. Given that the bulb glows constantly (but dimly) while the unit is on, is there any fresh ideas about where to look next or measure?

If I put the DMM to the DC side of the rectifier I read 54VDC coming out, which I don't know if that's high or acceptable.

[vortalexfan]

Originally Posted by starbond

Well i have some good news to share for once.
After getting my replacement Q4, the unit DOES power on now, although not fully.
When I flip the dim bulb switch the lightbulb lights for a second as the transformer starts and the vcr head whirs up for a moment, then the bulb goes out.
Once I press the power button the VCR then the bulb glows dimly the entire time the vcr is on. all of the front panel functions work excepct for part of the main screen VFD, the clock and time elements light but the orange PLAY FF RWD side does not. The whole thing runs weakly, I can put a tape in the transport and it will lower onto the spools and I can eject it, but Im guessing due to the bulb pulling current the unit is running not at full power.

I'm afraid to run the VCR without the bulb intermediary as I dont want to blow Q4 AGAIN. Given that the bulb glows constantly (but dimly) while the unit is on, is there any fresh ideas about where to look next or measure?

If I put the DMM to the DC side of the rectifier I read 54VDC coming out, which I don't know if that's high or acceptable.

Usually if the dimbulb glows dimly when something is powered on it means the item in question is working properly, if it glows bright and stays glowing bright then that means it still has a short in it.

[starbond]

Great news, the VCR is now up and running! Thank you everyone who helped me out on this and I hope this thread can serve as a guide for anyone in the future who is (foolish) enough to take on this task. Despite the noises i heard in the head, the video seems to be playing fine.

The next step is to work on the pinch roller, the audio is very fluttery and sure enough the roller is not catching fully. Also the rewind and fast forward belt which I assume is slipping a bit too.

[vortalexfan]

Originally Posted by starbond

Great news, the VCR is now up and running! Thank you everyone who helped me out on this and I hope this thread can serve as a guide for anyone in the future who is (foolish) enough to take on this task. Despite the noises i heard in the head, the video seems to be playing fine.

The next step is to work on the pinch roller, the audio is very fluttery and sure enough the roller is not catching fully. Also the rewind and fast forward belt which I assume is slipping a bit too.

That's great news! I actually think I had a VCR like that one time, that I got from my high school. I think the issues I had with mine was I had to replace the drive belts, and the idler tire, you might try that on yours.

I think I figured out the issues on the power supply on my VCR, it has a shorted bridge rectifier.

[vortalexfan]

My VCR's power supply uses a small S1WB-S4071 Bridge Rectifier and I tried Googling that number and I come up with no results, but when I just google the first 4 digits of the rectifer I come up with a bunch of results but not the exact one I'm looking for, what would be a modern equivalent to that part?

[starbond]

It seems the tape is pushing up just slightly too high on the tape path. Also inspecting the pickup side of the tape, it sits higher on the spool than the tape before it.
I'm hesitant to adjust the guide rollers, is that the only way to fix this? I dont even have a spanner tool for it.

[Ed in Tx]

What's the tape path look like at the guide just after the AC head? I've seen the vertical forward-back tilt or "zenith" of the AC head. or a worn pinch roller, cause tape skew.

If you go messing with the entry and exit rollers you will probably need an oscilloscope hooked to the head amp RF-out to do an alignment assuming you have a known good tape. Put a small mark with a felt tipped marker on the shiny metal part on top of each roller assy just in case, so you can put them back where they were.

[starbond]

Ed when i check the other end of the path it actually looks okay. If you say a worn pinch roller can cause the same problem then thats exactly what it is. I can see the tape start to spool out loose for a half a second before the roller pulls it back in but its a back and forth battle. I'll try some rubber restore but its pretty far gone. Problem is I dont know how to get it off the transport

Seems like all the rubber parts are in need of replacement. When FFD or RW sometimes the tape gets stuck despite the motor turning, When I press stop and the transport rollers go back in, the tape does not pull in those 3-4" of slack so If I were to hit eject Id end up with a snagged tape, I have to rewind or ffd first for a few seconds before ejecting the tape. Looking at the idler(?) roller between the two tape spindles its also pretty shiny and smooth.