Teac 80-8 total solenoid failure

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pacificmilk

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Teac 80-8 total solenoid failure

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I have been using a Teac 80-8 for the last 3 weeks.

Everything was going fine until the pinch roller started to engage intermittently and then needed to be manually engaged.

The motors are running fine. However, both brake solenoids and pinch roller solenoid have stopped engaging. The relays on the power supply are working the resistors feeding the solenoids are fine. There just seems to be no current going to any of the solenoids. Even when the plunger is pushed in (after selecting Play, FFWD or REW with take up arm in up position..) none of them will hold. I believe the solenoids are fine as I can get a good resistance reading from them. I have recapped the electrolytic caps in the power supply, but still nothing.

Any help would be greatly appreciated.
 
Is there a separate fuse for the solenoids on this machine? Do they move freely (some machines had a problem where the rubber grommets would melt and gum up the solenoid)?
 
I had a teac machine that had your original symptom. The pinch roller needed gentle persuasion.
I took it apart and degreased and lubed all the moving parts which reduced friction just enough to restore normal operation.

I wonder could a a fuse have gone with your solenoid being in limbo? Just a thought.
 
The solenoid plungers move freely with no resistance. The fuses register continuity with DMM. I just noticed that there are four diodes running really hot on the power supply board. They have discolored the PCB around solder points. I have tested them (without removing them from the circuit) and they seem to conduct in both directions.
 
Is the solenoid power portion of the power supply reading the right voltage?
 
If those relays are the same part# try swapping with each other to see
if the machine behaves differently.

Gary
 
pacificmilk said:
The solenoid plungers move freely with no resistance. The fuses register continuity with DMM. I just noticed that there are four diodes running really hot on the power supply board. They have discolored the PCB around solder points. I have tested them (without removing them from the circuit) and they seem to conduct in both directions.
Click to expand...
You may need to remove them from the circuit to get an accurate picture. (I was bitten by this on a Revox B77...)
 
Yes, diodes need to be tested out-of-circuit.

Also, 4 diodes grouped together sounds like an ac to dc rectifier. It's normal for them to get hot and yes even discolor the board.

Step 1: are the solenoids getting power when they should? I don't have 80-8 tech docs in front of me but I bet it's 24V, so put the machine PLAY and see if you have 24V DC reaching that solenoid. No juice? Trace back to the power supply and, with schematic in-hand, keep probing to you find the fault.
 
Check the fuse (F1) on the power supply reel motor control circuit board. If it is good verify +29V out on connection 15 on that same board referenced to connection 11 (0V). Report back.
 
While you are at it....

Are the 4 hot diodes D9 through D12 on the same board?
 
mdainsd said:
Check the fuse (F1) on the power supply reel motor control circuit board. If it is good verify +29V out on connection 15 on that same board referenced to connection 11 (0V). Report back.
Click to expand...

I checked that and got +29V.
 
On some advice from a tech via telephone earlier today I went about testing the individual solenoids. He seemed to think there was a possible short in one of them that was messing up the whole works. I first disconnected one lead from the pinch roller solenoid and fired up the deck but the other two solenoids would not engage. Then I disconnected one of the leads on the REW motor and set about just testing the take up solenoid. Nothing. I did find that if I manually engaged the solenoid it would hold, but it would drop out at random times. Also, after manually engaging the solenoid it would instantly let go if I connected either of the other two solenoid leads.
 
sweetbeats said:
Yes, diodes need to be tested out-of-circuit.

Also, 4 diodes grouped together sounds like an ac to dc rectifier. It's normal for them to get hot and yes even discolor the board.

Step 1: are the solenoids getting power when they should? I don't have 80-8 tech docs in front of me but I bet it's 24V, so put the machine PLAY and see if you have 24V DC reaching that solenoid. No juice? Trace back to the power supply and, with schematic in-hand, keep probing to you find the fault.
Click to expand...

I will try this in the morning as I need to take the rest of the night to refrain from cursing as well as let the iron burns on my fingers harden.
 
pacificmilk said:
On some advice from a tech via telephone earlier today I went about testing the individual solenoids. He seemed to think there was a possible short in one of them that was messing up the whole works. I first disconnected one lead from the pinch roller solenoid and fired up the deck but the other two solenoids would not engage. Then I disconnected one of the leads on the REW motor and set about just testing the take up solenoid. Nothing. I did find that if I manually engaged the solenoid it would hold, but it would drop out at random times. Also, after manually engaging the solenoid it would instantly let go if I connected either of the other two solenoid leads.
Click to expand...

This is a good clue. The solenoid is charged to engage and then "holding current" is supplied. It sounds like the current path that supplies the charge to engage the solenoid is not happening, and because its global to all the solenoids that could really help narrow down the problem schematically. I don't recall if the 80-8 uses relay logic or IC/solid-state logic. Either way you'll need to have a look at the logic board. I suspect the path that supplies power to the circuits that initially engage the relays has a fault.
 
IC logic. the relays in an 80-8 are dedicated to the reel and capstan motors.
 
schematic (2).webp

Here is a copy of the power supply board schematic with factory test voltages and as tested (hand written in blue ink) by me. It seems that the middle section ( 3, 4 inputs at 13V(section with the hot diodes)) is the only section working as it's supposed to. The voltage at the solenoids is about 1V.
 
Well it's fixed. After many hours with a tech we found the problem. It seems that the voltage regulator Q203 (above) had gone bad and needed replacement. Also IC2 (above) had gone awry. The price for the parts was minimal, but the labour, sheeesh!! Time to tighten up on the grocery bill. It is a relief to have her back. Thanks again to everybody who tried to help. You fellas are great.
 
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