So what is the "Panasonic power supply issue"?

[starbond]

Originally Posted by vortalexfan

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.

Thanks, I will look close when I pull the resistors again. I get a little anxious desoldering parts in and out because I have a tendency to rip the pads off the board due to my modest soldering skills and braid which never seems to suck up solder, but thats another story lol

One question now that I'm wondering after seeing your post about your VCR that was stereo but not hi-fi.. and this is addressed to anyone: After looking up linear audio VCR information, it mentioned how Dolby NR was used to compensate, but that was on linear stereo tracks (not hi-fi).
Now, this unit has Hi-fi AND Dolby NR. Was it just overkill or am I missing something here?

[Blast]

Originally Posted by starbond

--snip--
One question now that I'm wondering after seeing your post about your VCR that was stereo but not hi-fi.. and this is addressed to anyone: After looking up linear audio VCR information, it mentioned how Dolby NR was used to compensate, but that was on linear stereo tracks (not hi-fi).
Now, this unit has Hi-fi AND Dolby NR. Was it just overkill or am I missing something here?

Correct. Dolby NR was utilized only on the linear audio tracks. Not the HI-FI audio.

[vortalexfan]

Originally Posted by starbond

Thanks, I will look close when I pull the resistors again. I get a little anxious desoldering parts in and out because I have a tendency to rip the pads off the board due to my modest soldering skills and braid which never seems to suck up solder, but thats another story lol

One question now that I'm wondering after seeing your post about your VCR that was stereo but not hi-fi.. and this is addressed to anyone: After looking up linear audio VCR information, it mentioned how Dolby NR was used to compensate, but that was on linear stereo tracks (not hi-fi).
Now, this unit has Hi-fi AND Dolby NR. Was it just overkill or am I missing something here?

I do actually have a Hi-Fi VCR from 1987 but it's a Prosumer grade version of the JVC S-VHS VCR from the same time period (the one that had a simulated wood grain cabinet and had the large remote that had the flip open door on the bottom of the remote for the editing controls).

[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.

[vortalexfan]

Originally Posted by 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.

One thing I've had to do with these Pannys from this time period is that the idler tire has to be replaced (they are dry-rotted by now) and I know I had an old Panasonic 4-head Linear Stereo VCR from 1984 that I had picked up from a flea market several years ago for $10 that it had issues with wanting to "eat" tapes and also not want to rewind and fast forward tapes properly, at first I thought it was one of the 3 or 4 drive belts on the bottm of the unit, but when I checked them, they were fine, but then when I checked the idler tire, it was cracked and dry-rotted, so I got a new idler tire installed on the unit and its been fine since (a friend of mine has it now.)

[Ed in Tx]

That pinch roller is shot. No good. When I worked on those it was routine to replace the pinch roller and other rubber parts, idlers, belts. Often replaced the takeup clutch ass'y too, with OE parts. The aftermarket parts I tried usually came back to haunt me. Another wear part is the back tension band. I can almost guarantee there is excessive back tension on the tape because of a worn tension band. But that will be hard to find new and then you have to adjust the tension with either a special tape with a tension scale or a "Tentelometer" which I used.