80-8 Transport Problem

[lassoharp]

Hey

My trusty TEAC 80-8 seems to have given up the ghost recently. The problem started about a year ago. After the machine had been running for several hours, the rewind wouldn't work properly. I would hit rewind and nothing would happen though I could hear the relays engaging. After repeatedly hitting rewind it would finally work normally. This problem progressively got worse until a few days ago when it stopped rewinding completely. At the same time the play mode stopped working properly. It starts to play the tape but the capstan arm starts jerking wildly then falls causing the transport to stop. When I use my finger to hold the arm in place the take-up reel seems to stop and the tape just spools through the capstan and down the side of the machine.

With no reels on the deck, both take up and supply reels move as they should when play is pressed. Both FF and REW work normally with no reels on as well. I think I've ruled out sticky shed - tried 4 different known good reels with same results, cleaned tape path. I checked the big start motor cap in the back and it tested good. All three relays on the power supply board engage/disengage when the corresponding transport button is pressed.

It seems like the motors are functioning but aren't supplying enough torque. I don't have a schematic so I'm not sure where to start checking voltages. There doesn't seem to be any factory test points in this machine like you'd find in a pro deck.

I've heard there's a 'drive transistor' in the power supply that might be the problem but I have no idea where this is located. Seems there should be a switch for the motors themselves but I don't know where this is either.

Any troubleshooting suggestions for pinpointing this problem would be greatly appreciated!!

[TapeOpLarry]

Keep in mind that any tape transport is a device in a delicate balance. In order for the (mechanical or electronic) logic to engage the deck in play or shuttle the tensions on the arms and reels must all be appropriate. If a drive transistor or motor is out this will throw it off. If a sensor is erratic or broken it will be thrown off. A mechanical part could be out of whack or broken.

A service manual is a must in order to really set this deck up right, and if I'm not mistaken most of these "pro-sumer" decks were shipped without one. When I've run into transport issues like this with my Otari or MCI decks I've usually ended up calling in a tech to troubleshoot this. I used to fix my JH-16 myself but that was like repairing a 55 Chevy! Clunky and obvious stuff.

[lassoharp]

Was luckily able to find and fix this problem.

The apparent cause was the solenoid housing - located on the rear of the reel motor - had slipped out of position towards the left causing the solenoid plunger to disengage incorrectly(thus keeping the brakes from disengaging during Play/Rew/FF).

Fixing it was a relatively simple matter of loosening the set screws and adjusting the physical position of the housing slightly towards the right.

[TapeOpLarry]

Oh yeah, solenoids can be very buggy if out of alignment. I once had on in an MX-80 that I assumed was dead, replaced it with a new part and same problem. Turned out it just needed to be scooted over a tiny bit and everything started working fine.