Making myself hysterical with piano key VCR's

[TUD1]

I don't even know what I'm doing anymore. I cleaned up my Panasonic PV-1200 yesterday, only to somehow knock the counter belt off the pulley which (I now know) causes the machine to play, but subsequently stop because the counter isn't moving. So I spent about two hours turning the machine every which way to get it back on. In the process, I broke the SP-LP-SLP switch. After that, I decided to work on the VDT-501 because it had the same problem. After much fooling around, I smashed the sensor lamp, and broke the counter belt completely. Now I'm in deep doo-doo with these things. I need four light bulbs (LED substitutes anyone) 2 new counter belts, and a speed switch. I dare not touch the VBT200 until I stop breaking stuff.

[walterbeers]

I don't think there is any LED substitute for the sensor bulb. It is wired into part of the circuitry so that if the bulb burns out (or gets broken) the unit will not operate. Also wired into the counter is a small magnetic wheel that senses if the counter is running, which also proves that the take up reel is turning. There again, unit will not operate without the counter belt and counter working. I believe you can find belt kits for numerous VCR models, and also sensor bulbs, which should be listed by model number. Just have to google it. Don't feel bad, I've broken many different parts through the years while trying to fix things.

[walterbeers]

For the belt kit for your Panasonic PV-1200 the kit is listed on the link below under RCA belt kit. I bet they also have a sensor bulb for it as well.
http://www.smcelectronics.com/vcrbltkit.htm

[TUD1]

What if I measured the resistance of the sensor lamp and installed a resistor alongside a small LED?

[Captainclock]

I think I might have some of those sensor bulbs laying around in my basement that I could sell you for the price of shipping. they're basically a grain-of-wheat bulb with a small plastic base built into them. The bulb is made by Oshino Electric Lamp Works, LTD of Shinagawa Prefecture, Tokyo Japan. and the bulbs themselves are marked with a part no. OL-815BP 5V 115mA.

[TUD1]

I figured out what the problem is with the VBT200. Here is a video demonstrating the unit.

[Ed in Tx]

I would start by cleaning the rec-play slider switches making sure they are OK, then look at the drum servo signals, and do an alignment of the drum and capstan servos. You need the service manual and an oscilloscope to do those alignments.

[TUD1]

I have the service literature and access to an oscilloscope, but I wouldn't know how to use it or what to look for. On my Betamax SL-5000, I remember there being a drum speed potentiometer. I thought I could just adjust that?

[Ed in Tx]

Probably the same alignment but you were just hit and miss without proper hookup and procedure. This is something you need to learn how to do on those old machines. I can almost guarantee 100% all of them will need some touchup of the drum and capstan servo alignments.

Needs to be set to the center of the PLL servo range which is what the alignment does, so the drum comes up to speed and locks to speed properly. The head switching point is effected by this too so you may find a close point by watching a known good videotape and adjust the drum servo so the switching is just visible a few h lines above the bottom of the picture. Could also be the 3.58 oscillator or it's trimmer capacitor being off or intermittent. Looked like something was drifting off freq watching that video, until it lost sync completely.

[Gunslinger]

reduce your vertial height and look at the head switching at the bottom of the Tv picture. See if it changes when the problem appears. When these units were just a few years old, the head switching points needed adjustments.

[Ed in Tx]

But before you decide the head switching is off, you need to make sure the cylinder servo is correct because it affects the switching point.

If I had the schematic for the head servo and the capstan servo ICs, there is a pin on each IC that should be very close to 4.7 V when the servos are correct.

[TUD1]

I found this in the service literature.

[TUD1]

The VBT200 is fixed! I turned the drum speed pot and just as I predicted, the picture came right in and is crystal clear. Here is a video.

However, I'm still having a really weird problem that I cannot explain. It's almost like the VCR says to itself "Okay, I'm tired - I quit." Then, all the functions work very poorly or don't work at all. Earlier today, the FF, REW, and play were all very strong with no hesitation whatsoever. I was watching The Wizard of Oz, and all the a sudden, the picture froze, like pause on a newer VCR, and all the functions stopped working completely. The play key would not lock, and the FF and Rewind became very weak. And then, when I let it sit for half an hour to an hour, it begins working perfectly once again. I was informed that there are little bitty contacts, the "mode switches", that control the electronic section of the function. I doubt that these are the problem though, as I did clean them with DeOxit, and all the functions come and go suddenly. I'll put up another video tomorrow if anybody needs it to help them understand the problem.

[Ed in Tx]

If all that starts happening together like you described, I would speculate a power supply problem.

[TUD1]

Capacitors? At least it's not those servos. I took a Betamax SL-8600 to a now defunct TV service location years ago, and they said it was unrepairable due to bad servos.