M90 deck help ! (continually clicking)

[docs]

Hi all,

On powering up it clicks continually. I have replaced FR704 (4.7ohm 1/2watt) which was toast as is common on these decks.
The capstan is turning continuously so the motor is powered ok.

I checked out Q712 just to be sure and all looks ok there to me.

Even though the capstan is turning, Q709 seems to give iffy volt test results.
The base should be 0.3v, the collector 5v and the emitter 0v.
I do read 5v out of pin 18 on IC701.
Readings are, base 1.44v, collector 0.8v and the emitter is 0.74v.
However, doing diode check on this transistor seems to check out as ok while Q710 diode test looks bad in circuit (tested out of circuit seems to test fine).

So even though the capstan is turning, could it be that Q710 would cause the continuous clicking ?
Any help appreciated.

 

[BoomboxLover48]

I have a nice M90 but never had issues like this.

I know little about M90 issues I wish I could help!

Hopefully Superduper (Norm) or our other experienced members will chime in and guide you through fault detection.

Good luck docs!

 

[docs]

Thanks BbL appreciate it.

 

[Northerner]

Crikey Dave you're up early!

 

[Superduper]

Sounds like a mechanical problem to me. Make sure belts are not loose. Also clean and make sure the solenoid plunger is free and not gunked up. On power up, the M90 deck makes 1 cermonial turn around the block to "reset" things. Your deck is not resetting, hence the merry go round.

As for the capstan driver circuit, I see nothing wrong there.

 

[docs]

Hi Norm, will look at that solenoid sprung section and check the mechanics in more detail.
With a tape in it doesnt click continually but the functions dont work. Pressing play locks the deck door.
Will also thoroughly check the belts.
Cheers.

 

[docs]

Belts are good, I can freely move the solenoid and the little plastic bar on top of it is the piece moving in and out causing the clicking noise. I haven't gone any deeper yet into where the solenoid is but it seems to move freely.

Anything obvious you can see from these or other photos which might help ?

 

[Superduper]

M90 deck buttons normally will not respond without a tape in it, so your tape presence sensor seems to be thinking the opposite is true. Something is reversed.

 

[docs]

Interesting.
Is this the tape sensor or is it something mechanical from where the cassette is inserted ?

 

[docs]

Pressing the sensor pad stops the deck continually clicking, release it and it continually clicks again. I notice the sensor light is off when pad is pressed and on when not pressed. The drive gear assembly seems to be in order and I can't see if there is anything untoward.
I'm guessing noone has detailed deck photographs, can't see any on the forum already.

 

[baddboybill]

That's sensor for auto stop I believe. The tape sensor that Norm I think means is a switch that is pressed in when tale is in tray and closed


Bad Bad Bill

 

[baddboybill]

The clicking is solenoid pulling in and releasing back out over and over. It actually is suppose to just pull in when you power unit on.


Bad Bad Bill

 

[BoomboxLover48]

M90 and M80 decks seems identical. I played with an M80 for a long time before I fixed it all.


Are you sure the gear under the flywheel is engaged with the lower toothed wheel mechanism?


The lower tooth wheel is the one that activates all the tape deck mechanism.

This will never happen without the plate on top of the flywheel in place.

This is all based on my experience with the M80 deck. I could be wrong!

 

[docs]

Yes the cog under the flywheel engages the gear and the entire mechanism engages the solenoid.
There is a point where the gear is reset but its position makes no difference to the clicking and it doesn't reset.
What I have noticed is the solenoid is not being pushed all the way in but it does seem free enough.
I can't take the piece off with the solenoid plate because of a threaded tiny screw for that section.
I'll try and work it more with some cleaner but seems like the lever that is meant to push it in isn't strong enough to push it all the way in.
If I manually push the solenoid in the deck stops clicking though I think functions still don't work will check this later.

 

[baddboybill]

Yes the cog under the flywheel engages the gear and the entire mechanism engages the solenoid.
There is a point where the gear is reset but its position makes no difference to the clicking and it doesn't reset.
What I have noticed is the solenoid is not being pushed all the way in but it does seem free enough.
I can't take the piece off with the solenoid plate because of a threaded tiny screw for that section.
I'll try and work it more with some cleaner but seems like the lever that is meant to push it in isn't strong enough to push it all the way in.
If I manually push the solenoid in the deck stops clicking though I think functions still don't work will check this later.


Actually the solenoid becomes magnetized and pulls pin in which pulls lever your speaking of. Sounds to me like solenoid isn't staying magnetized fully like its suppose to to hold pin in


Bad Boy Bill

 

[docs]

Let me get some close up pictures of that section see if you can spot anything untoward with how it is setup.
There is a piece on top of the solenoid lever which I thought would be used to push it in since it is spring loaded. Charging camera battery then will post some pics

 

[docs]

 

[baddboybill]

Did you replace diode D752 on small board where solenoid is attached? Looks like solder was disturbed


Bad Bad Bill

 

[docs]

I tested it out of board and have left it rough for now but am sure it is ok. Will tidy up this solder.

 

[baddboybill]

I tested it out of board and have left it rough for now but am sure it is ok. Will tidy up this solder.


Oh I was just asking, so diode tested good? And when you push pin barrel inside of solenoid there is no blockage and it freely moves all the way?


Bad Boy Bill