Supertech 747 Super Jumbo Tape Decks Dead

RaleighRon

RaleighRon

New Member
Picked up a 747 Super Jumbo. Everything works but the tape deck motors do nothing.

1. Tested the micro switch and have power there. 2. Also tested the wire tabs at the motors and getting power there.
3. Desoldered a motor and tested it and it comes on wired direct to a battery
4. When I do push play the micro switch completes power but motors still do nothing.
I am not sure what to check next. Anyone ran into this before?
I have a nice cassette collection and like my Boxes 100% functional.
 

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Tinman

Tinman

Member (SA)
You're getting 12v at the motor boards when it's installed but they're not running?
You applied 12v at the motor boards when it was removed and they run?
 
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Ghettoman

Ghettoman

Member (SA)
The most common fault with those decks, the potentiometers go bad on the small board that controls the speed, i've had about 5 of those J747 super jumbo's over the years and on every one of them i had to change the bad Vr's, i think you get 2x 500k, and 2x 1k (i think) it's years ago since i repaired one, also, be careful with those graphic sliders while putting it back together, they are so easy to snap and break. the super jumbo is a nice box but they are so flimsy and cheap, not as bad as the crown Sz5100, but certain parts on them are easy to break
 
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Tinman

Tinman

Member (SA)
Are they both showing 7v?
It looks like there are multiple wires, at least one should be 12v+ and one has to be ground.
The others might be used for some kind of speed control which I'm not really familiar with.
I've never seen a motor case with voltage.
 
RaleighRon

RaleighRon

New Member
Tinman said:
Are they both showing 7v?
It looks like there are multiple wires, at least one should be 12v+ and one has to be ground.
The others might be used for some kind of speed control which I'm not really familiar with.
I've never seen a motor case with voltage.
Click to expand...
Yeah the last wire which is blue is soldiered to the last motor tab which also is soldiered to the motor case. Its hot. No idea why. Starting to wonder if its something to do with them swapping the transformer at some point o make it 110V instead of 220v. Another thing is when I touch a ground to the red wire going to the motor the motor starts spinning but only while grounding it out. I see nothing burned, broken or loose anywhere. Radio works great, alarm, lights etc. Just this weird stuff with the tape decks.
 
Tinman

Tinman

Member (SA)
If you don't have a service manual for it, I'd remove all wires and start from scratch.
Figure out which is ground and which is positive.
Ground is easy.
Positive (at least 12v) is powered on play, rew or ff.
I assume red is positive but who knows what's going on in there since you know it was messed with electrically.
Again, I'm not sure what the other wire's functions are.
 
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Superduper

Superduper

Moderator
Staff member
You need to understand, that is a 4-wire motor. It does not at all behave like a 2-wire motor. Also, without knowing more about the circuitry that was designed around it, it's would be unwise to make presumptions simply because it's not behaving like you expect. For example, the common 2-wire motors we are accustomed to have internal speed controls that is accessible through a shrouded mini pot. These 4-wire ones have external speed controls governed by circuitry not within the motor. Then there's the method of sourcing V+ and ground. You are presuming that ground on the motor is tied to ground. It may, or may not be. You need to check to be sure. It is not at all uncommon for a motor to be switched through a transistor, and those types of circuits source ground differently than one that's tied directly to ground. In these scenarios, ground (motor chassis) might be floating until it's actually sourced a ground by an activated transistor. Also, if a motor (-) is normally tied directly to ground, and if the ground has a bad connection, it is not at all uncommon for that point (motor (-) to show positive voltage, because in that scenario, you are measuring voltage drop across the connection.
 
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Tinman

Tinman

Member (SA)
The odd thing is Ghettoman said above that these motors have adjustable speed controllers.
It's confusing to me why they have the extra wires.
Would a speed adjustable motor also have an external speed control?
 
Tinman

Tinman

Member (SA)
caution said:
These have high speed dubbing. Pretty sure that dual-speed motors have 3-4 connections.
Click to expand...
Ok, I didn't realize it had HSD, in the 30+ boxes I've worked on I've never dealt with that.
I have run across a few multi wire motors but luckily never had a problem with any.
 
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