Zenith VR8900W (rebadged Sony SL-5000) reel motor supply issue (need a schematic) - Videokarma.org TV - Video

Electronic M · #1 12-03-2020, 02:49 PM

I'm working on an early front load Betamax deck.
There's a motor that drives both cassette reels and the threading mechanism. After going over the belts it will rewind and fast forward like a champ and usually thread tape (sometimes it plays dead) but it won't opperate the take up reel in play mode... checking the voltage to the motor I have figured out that the reel motor gets around 10V in all modes where it should run except play mode where it gets 2.5V...To confirm the issue was electrical instead of mechanical I took an external 7V supply and hooked it to the motor as soon as play was pressed and the take up reel worked well for the couple minutes I tested it for.

The board that feeds this motor is hard to get at(the least accessible board in the deck) and I suck at troubleshooting solid state devices without a schematic...does anyone know where I can find or happen to have a copy of the repair manual (Sam's, Zenith, Sony)? I really need a look at the schematic of the control circuit for the reel/threading motor and instructions for accessing the board.

Electronic M · #2 12-04-2020, 10:10 PM

After going through a proceedure on youtube to fix the capstan and head drum speed issues by replacing the light blue caps on the SS-9 board and adjusting speed pots I ended up breaking the head drum drive circuit trying to puzzle it out.

Earlier today I decided since I had been able to force it to play a tape well and I have a second identical one that it was worth springing for the overpriced blurry Sam's for it.
Several bad NPN transistors on the SS-9 board were the cause of several lines being locked in various undesirable states...Q522 which was causing the low reel motor play voltage temporary fixed things but it relapsed and I ended up adding an 820 ohm in series with the collector to limit the pull down that transistor could achieve.

It works now...now to try and make the other deck work.

Telecolor 3007 · #3 12-06-2020, 11:56 AM

By curiosity what apparatus is the one above the tv sets with 2 knobs?

Electronic M · #4 12-06-2020, 08:50 PM

Quote:

Originally Posted by Telecolor 3007

By curiosity what apparatus is the one above the tv sets with 2 knobs?

The silver and black thing on the right side of the running TV is my bench stereo. It's an Akai with radio, phono, and tape(dead) which is remote controlled. The only remote phono I own.
Left of it the almond thing that looks like a scope is a Heathkit test pattern generator with vector scope.

Telecolor 3007 · #5 12-07-2020, 06:58 AM

By curiosity, does that turntable haves a drawer, meaning in order to change the record, you don't rise the lid, but the turnatble (not the electronics) are coming outside?

Electronic M · #6 12-07-2020, 10:02 PM

Quote:

Originally Posted by Telecolor 3007

By curiosity, does that turntable haves a drawer, meaning in order to change the record, you don't rise the lid, but the turnatble (not the electronics) are coming outside?

Yes.

It is a good sounding unit but internally it's a nightmare to service. Early on I gave up changing the tape deck belt because it was so buried. I almost threw it out when it blew a speaker fuse because the blasted fuse is on a circuit board that you have to disassemble 3 other hard to remove boards to reach. The engineer or bean counter that decided not to put the speaker fuses on the back or atleast make them take less than 3 hours to get at should have been tasked with replacing every blown fuse in the sets that came in for service as punishment IMO.
Another oddity of it is the european style FM antenna coax connector (somehow I had an adapter in my hoard) despite having the american FM band and AM channel spacing.

I've got sort of a love-hate relationship with the thing.

Electronic M · #7 12-07-2020, 10:12 PM

I gave up fixing the twin of my Zenith. It had worse problems than the one I fixed had and additional things broke that blocked troubleshooting the initial known problem... There's a chance I could have fixed it but I wasn't going to keep 2 identical VCRs and the unit isn't worth the time I already gave it.

I've moved on to a Sony SL-5600 that uses a single motor for capstan and threading. The motor was stuck (I think it's free now) and it isn't getting power...I may try to fix it without a schematic but I may have to buy one.

Electronic M · #8 12-08-2020, 02:57 PM

Well I got the SL-5600 working. Before lubing the capstan/threading motor I didn't find any voltage on its 2 top terminals (the bottom connector is too hard to get a meter on). After lubing the motor I couldn't figure out how to make it work on the bench, resistance were 200 ohm at lowest so I figured it was shot. I reassembled the mech and decided to try a tape...to my disbelief it threaded it and then played it back just fine.

Tuner won't pass decent video from the antenna (snowy negative without color) but it tunes sound fine. I'm probably going to leave the tuner alone for now since it doesn't really NEEED a tuner. Tape playback is enough to make me happy.