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TRC 975 decks not functioning!


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#1 FWSnake

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Posted 20 April 2017 - 09:38 PM

Both decks A & B don't play tapes at all. Radio and other features work fine, it's just this. Hopefully it's just something like the belts having to be replaced. I have some pictures if that helps anything.

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#2 JVC Floyd

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Posted 20 April 2017 - 09:59 PM

You should start by checking if the motor spins, if it does then you probably need new belts.

#3 Fatdog

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Posted 20 April 2017 - 11:58 PM

You should start by checking if the motor spins, if it does then you probably need new belts.

^^ This.  :yes:



#4 FWSnake

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Posted 21 April 2017 - 01:45 PM

And what if the motor does not spin (haven't checked if it does yet)?

#5 Hisrudeness

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Posted 21 April 2017 - 01:51 PM

Then you need to fix the motor too. When you switch the box on and press play does the motor do anything?

#6 FWSnake

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Posted 23 April 2017 - 03:51 PM

Then you need to fix the motor too. When you switch the box on and press play does the motor do anything?

Just got back to it. Upon observation, nothing is spinning when I activate the deck(s). You're likely right about fixing the motor, but I don't have the foggiest notion on how I should start with that.



#7 jimmyjimmy19702010

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Posted 23 April 2017 - 04:18 PM

Check for power at the motor first.

#8 FWSnake

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Posted 23 April 2017 - 06:27 PM

Check for power at the motor first.


The motor makes a little humming noise when powered on.

#9 jimmyjimmy19702010

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Posted 23 April 2017 - 06:49 PM

Try turning the motor over by hand with the drive belt removed. Dry/sticky bearings can cause a motor to seize. Drop a couple drops of machine oil into the top bearing and turn the brass pulley whilst pulling it in and out slightly.

On the other hand, sticky belts or a stuck deck mechanism can cause similar issues. It's a basic deck with one motor doing the duty of two motors in better decks. So you've probably got two main drive belts running from the one motor so either deck can be causing issues.

#10 FWSnake

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Posted 24 April 2017 - 12:02 PM

Try turning the motor over by hand with the drive belt removed. Dry/sticky bearings can cause a motor to seize. Drop a couple drops of machine oil into the top bearing and turn the brass pulley whilst pulling it in and out slightly.
On the other hand, sticky belts or a stuck deck mechanism can cause similar issues. It's a basic deck with one motor doing the duty of two motors in better decks. So you've probably got two main drive belts running from the one motor so either deck can be causing issues.

I'll try what you suggested. Is this solution supposed to fix the problem entirely or will there be an extra step or two afterwards?

#11 Fatdog

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Posted 24 April 2017 - 01:33 PM

I'll try what you suggested. Is this solution supposed to fix the problem entirely or will there be an extra step or two afterwards?


I guess we'll find out. :-D ;-)



#12 FWSnake

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Posted 25 April 2017 - 08:50 PM

Try turning the motor over by hand with the drive belt removed. Dry/sticky bearings can cause a motor to seize. Drop a couple drops of machine oil into the top bearing and turn the brass pulley whilst pulling it in and out slightly.

On the other hand, sticky belts or a stuck deck mechanism can cause similar issues. It's a basic deck with one motor doing the duty of two motors in better decks. So you've probably got two main drive belts running from the one motor so either deck can be causing issues.

It seems like you have to take apart the whole deck mechanism to actually be able to remove the motor. And after some searching, I wasn't able to find any brass pulley. How would I go about accessing it? 

 

Really wish there was a service manual for this  :drool:



#13 Helmar

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Posted 26 April 2017 - 01:32 AM

You do not need a service manual once you have the tape mechanism in front of you like on the pictures you showed.

However you need a structured way of checking and fixing the error.

Did you check by using a multimeter if there is any voltage on the motor after pressing play?

Are you able to rotate the motor manually be hand?

At this point you do not need to take the unit apart. Maybe only some cleaning and sanding of the microswitches is required.

 

Best regards

Helmar



#14 Superduper

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Posted 26 April 2017 - 02:08 AM

I'll bet all you need to do is replace the belts.  The humming of the motor is almost certainly due to it spinning.  The belts are probably just slipping on the pulley.  Service manuals typically don't give you a step by set on how to rebelt anyhow because in general, it is presumed that the technician possesses the mechanical aptitude to perform this simple task.  You're going to need further disassembly beyond that if you really want to replace the belts though.  If you can't overcome that hurdle, then we probably can't help you.  You can't fix something by looking at it.



#15 Helmar

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Posted 26 April 2017 - 06:43 AM

The tape mechanism looks very similar to Hitachi 3d80/88. There, one can change the belts without taking the unit apart or removing the motor.



#16 Superduper

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Posted 26 April 2017 - 08:28 AM

The tape mechanism looks very similar to Hitachi 3d80/88. There, one can change the belts without taking the unit apart or removing the motor.


Well you might want to share the steps or at least greater details of your process then because the OP obviously needs help, he basically says he doesn't know where to start.

#17 FWSnake

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Posted 26 April 2017 - 01:11 PM

You do not need a service manual once you have the tape mechanism in front of you like on the pictures you showed.

However you need a structured way of checking and fixing the error.

Did you check by using a multimeter if there is any voltage on the motor after pressing play?

Are you able to rotate the motor manually be hand?

At this point you do not need to take the unit apart. Maybe only some cleaning and sanding of the microswitches is required.

 

Best regards

Helmar

Haven't used a multimeter to check for a voltage output, but shouldn't the humming imply that there IS voltage coming from the motor anyways?
The motor cannot be rotated manually by hand. I figured I would have to take apart the drive mechanism to actually remove the motor and try jimmyjimmy's suggestion.

As for cleaning microswitches, I'll try that out as well.

 

I'll bet all you need to do is replace the belts.  The humming of the motor is almost certainly due to it spinning.  The belts are probably just slipping on the pulley.  Service manuals typically don't give you a step by set on how to rebelt anyhow because in general, it is presumed that the technician possesses the mechanical aptitude to perform this simple task.  You're going to need further disassembly beyond that if you really want to replace the belts though.  If you can't overcome that hurdle, then we probably can't help you.  You can't fix something by looking at it.

Guess I'll get a set of belts and try that out. Replacing belts won't be a problem, especially if Helmar is correct with the deck's similarity with the Hitachi model.



#18 Helmar

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Posted 27 April 2017 - 01:11 AM

You are right, I overlooked that the motor is humming.

So voltage and mircoswitches are probably OK.

Is the motor rotating or is it somehow blocked?

After removing 2 of the belts you can find out if the motor is blocked or the gears it is driving-

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#19 hopey

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Posted 27 April 2017 - 05:01 AM

I have seen this mech before and was rackin my brain. It's the same as sharp xbass left deck auto stop right deck auto reverse. It's the belts alright and there is also a stupid flywheel brake that gets in the way. Also the tape speed was different between the decks as you can see one motor and two different mechanical loads. sharp gx-cd60ht

I sucsessfully got this one working. It may be just the fly wheel brakes but I replaced the belts any way. There is also a plastic guide which you have to navigate the belt through. You can do all this without dissembling the mech. I actually cut the head off the brake stop with a snap blade which also releases the spring. The stop is made redundant but is only to stop the fly wheel turning in transit. After doing this both decks started working but you should replace the belts as well. I made up custom belts to suit.

#20 FWSnake

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Posted 27 April 2017 - 05:18 PM

You are right, I overlooked that the motor is humming.

So voltage and mircoswitches are probably OK.

Is the motor rotating or is it somehow blocked?

After removing 2 of the belts you can find out if the motor is blocked or the gears it is driving-

It ceases to rotate, meaning it is being blocked or obstructed by something.



#21 hopey

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Posted 28 April 2017 - 07:16 AM


You are right, I overlooked that the motor is humming.
So voltage and mircoswitches are probably OK.
Is the motor rotating or is it somehow blocked?
After removing 2 of the belts you can find out if the motor is blocked or the gears it is driving-

It ceases to rotate, meaning it is being blocked or obstructed by something.
A better response would have been. Thanks for the Helpful instructions, I have removed the belts as you instructed and now confirm the motor is not turning when powered up with no belts. However I can spin the motor by hand so it not seized.

If this is what you have done you may be able to service the motor or replace with a similar one.

#22 Helmar

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Posted 28 April 2017 - 07:30 AM

I would double check the voltage on the motor and -if ok- try to unblock the motor by putting some penetrating oil on the front bearing of the motor.

Then turn it by hand with slight force. Not much to loose anyway.



#23 FWSnake

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Posted 13 May 2017 - 08:20 PM

Well now it seems like the motor can be turned by hand easily. When turned on, the mechanism does nothing. I used a multimeter to look for voltage and there's nothing leading up to the motor. So the motor isn't being obstructed, it's a voltage issue. Could the motor connector be shorted out or corroded?

#24 JVC Floyd

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Posted 13 May 2017 - 08:25 PM

Another thing to check is the high speed dubbing switch , when they go wonky nothing works right.

#25 FWSnake

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Posted 13 May 2017 - 08:52 PM

Ahh, so that's been known to be a little iffy. I'll check the high dubbing switch for voltage. I honestly hope this is just a matter of cleaning out corroded bits or re-soldering something, because it would be a damn shame if I had to replace the entire circuit boards. Gonna guess these parts aren't too prevalent...

#26 FWSnake

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Posted 30 May 2017 - 08:19 PM

Another thing to check is the high speed dubbing switch , when they go wonky nothing works right.

Been away from my box for a while, gonna get back to it sometime this week, hopefully. In the event that the high speed dubbing switch is in order, what should I do? And if it's not? What should I look out for? Thanks.



#27 Lasonic TRC-920

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Posted 30 May 2017 - 10:11 PM



Another thing to check is the high speed dubbing switch , when they go wonky nothing works right.

 

This is true, some deoxit contact cleaner spray and compressed air in the button switch may help.

 

Also check the record bar. It looks like this....(this is not from the same radio, but these all look the same). Clean this with contact spray as well.

 

Attached File  IMG_20170531_060639.jpg   120.91K   0 downloads



#28 FWSnake

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Posted 01 June 2017 - 07:58 PM

Another thing to check is the high speed dubbing switch , when they go wonky nothing works right.


This is true, some deoxit contact cleaner spray and compressed air in the button switch may help.

Also check the record bar. It looks like this....(this is not from the same radio, but these all look the same). Clean this with contact spray as well.

attachicon.gifIMG_20170531_060639.jpg
Record bar has been cleaned, doesn't seem to be affecting much. At this point, I'm thinking that the motor needs to be replaced. Or worse, other parts.

EDIT; of further looking, the wires connecting directly to the motor are very weak, almost being binded by one tiny strip. These need to be re-soddered. Even then, voltage should be coming out of the motor.

#29 FWSnake

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Posted 01 June 2017 - 08:18 PM

Another thing to mention, the point where the motor wire starts is producing no voltage, as well as a brown wire that leads to a different point in the deck. I'm at the point where I believe there might not be a good solution other than an overhaul of all these parts

#30 FWSnake

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Posted 10 June 2017 - 09:19 PM

Update: Safe to say that there's no known solution yet. Unless anyone has some magical solution--or someone wants to pay a visit and help me diagnose the issue, I'll be putting it back together.