#31
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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? |
#32
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#33
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#34
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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.
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#35
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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. |
Audiokarma |
#36
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#37
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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. |
#38
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I think I figured out the issues on the power supply on my VCR, it has a shorted bridge rectifier. |
#39
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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?
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#40
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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. |
Audiokarma |
#41
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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. |
#42
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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. |
#43
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#44
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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.
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