TPR-990H Left channel dead

[Tubejunkie]

Hello my fellow boombox enthusiasts! As you can see by the thread title, I have a Aiwa TPR-990 that has no audio coming out of the left speaker on radio mode. I cannot attest to whether the left speaker will produce sound on any other mode because the tape teck needed new belts. Here's what I have done so far:
Recapped entire boombox, yes all 118 of them (I know... I'm crazy)
Sprayed the heck out of the mode switch and slid it back and forth about 50-75 times (till I lost circulation in my fingertips basically)
New belts all around.

Now here's what's going on:
1. The tape decks' soft touch buttons are jammed, frozen, will not move at all.
I've taken this thing apart and reassembled it about 10 times and no matter how I adjust the gears in the MD-1 mechanism it's always met with the same result in the end.

2. No audio from left speaker in radio mode.
When I have it in "tape" mode and spin the motor drive mechanism by hand, the "play" actuates and the "play" symbol light comes on but the cassette gets tangled in the pinch roller on the bottom right of the cassette assembly. All the while I can hear light "crackling" sounds emitting from the left and right speaker whether or not there's a cassette in the deck (the "balance" is centered during this time). I've tried to lubricate and clean the "balance" potentiometer but it is a PAIN to get to (you have to strip the inside clean of nearly ALL the parts.)

Any help will be very much appreciated as I am about an inch away from throwing it against the wall. Thanks!

 

[hopey]

Wow sounds like you have been busy. It's a funny thing but the problem can be as simple as a dirty contact inside the mode or function switch. I have just completed on such example I was losing one chanel on tape only now fixed.

There are many others on here who know a lot more than me about your radio.

 

[docs]

Every 990 I’ve repaired with a dead channel has always been the dolby IC for that channel.
You need to confirm if you have any audio in that channel on any function. Try line in.
I haven’t checked the schematic but just saying I’ve done 4 or 5 with same dead channel issue.

 

[Tubejunkie]

Thank you very much for your insight! I will definitely try that out and keep you guys posted!

 

[Tubejunkie]

Well I tried the "line in" and both channels are working great. (Thank you very much for the advice "docs"!) But I'm still stuck as far as configuring the MD-1 mechanism. Does anybody know how the gears are arranged from the factory? (as in "before I took this thing apart and screwed it up") I've tried many many different configs but the "soft-touch" buttons are still stuck Thanks.

 

[docs]

The gears must be located in their reset position (the reset position can be seen in the service manual).
Also before screwing the lower gear case down, there is a lever running along the top towards the front case which can get trapped and must be checked to ensure it is free before screwing the section in place.

 

[Tubejunkie]

Well, I got the service manual but there's no mention of a "reset position" that I can see. Would I be violating any forum rules if I post a couple of pics of the service manual?

 

[Tubejunkie]

BTW the audio issue turned out to be a dirty balance potentiometer.

 

[Josh9994]

I assume if you turn the flywheel the belts turn with your fingertips the gears will turn and eventually get to the reset point once the gears stop moving and you hear the click of the reset of the buttons. Make sure you are turning that flywheel the same way as the motor would turn it.

 

[Tubejunkie]

Josh9994, thanks for the response. I did spin the flywheel but none of the gears moved. My guess is that the motor that spins the flywheel is dead or receiving no voltage. I'll do a voltage test and report back in a bit.

 

[Tubejunkie]

Here's a link for a video of what's going on. I pressed play on the feather touch button and then manually spun the flywheel.

 

[Tubejunkie]

If anyone has any clue as to what's going on I would be very grateful Thanks

 

[hopey]

You said you replaced all belts what about the motors? These can be serviced and regain the torque and rpm required to exercise the mech.

 

[docs]

When you press play, it would probably actuate a leaf switch to turn that motor on, I can't fully remember.
If this is the case, then check that leaf switch and check voltages to that gear motor.
Assuming all the gears are in the right place and the lever close to the front case on that section moves freely, the leaf switch/motor might be the issue.

 

[Tubejunkie]

Much thanks to "hopey" & "docs"!
To Hopey: The motors seem to operate as should based on the fact that the guy aka my brother (who's also a self proclaimed tech such as myself lol) told me that before he replaced all 3 belts in the tape mechanism the cassette function worked just fine but since the belts were gooey before the repair, it would work for about 2 seconds before turning off. My brother handed this boombox off to me disassembled because he has a mountain of work and figured it would be best for me to reassemble it.

To Docs: Do you happen to know where that "leaf switch" is? I have a copy of the service manual but due to designs from the early 80's the diagrams leave much to be desired (aka crappy images). I can upload it in it's entirety if that helps.

 

[Josh9994]

You first need to check that you are getting voltage at the motor when you press play, fast forward, and rewind. Almost sounds like the motor is needing oil. I like to oil the motor with the belts off and the motor on, I let it turn freely for 5 minutes or so.
You might have to oil the motor and clean and oil and or grease and moving parts that are associated with the belts turning.

 

[Tubejunkie]

Thanks for your feedback Josh9994. I'll check it out to make sure the motor moves freely. It seems to me that I'm going to have to disassemble the whole mechanism in order to get to that motor. I'll keep you posted

 

[Radio raheem]

I can tell you this, it's the buttons that are soft operation NOT the deck, it's a crazy design, hope this helps

 

[Tubejunkie]

Thank you for that bit of information Radio raheem, I had no idea! This radio is by far the most involved/difficult one I've ever worked on.

 

[Radio raheem]

Thank you for that bit of information Radio raheem, I had no idea! This radio is by far the most involved/difficult one I've ever worked on.

i have never had one for this reason, but several people have told me this over the years....the buttons being soft operation them selves makes this a very hard job

it's the strangest idea i have heard of, good luck dude