tascam 32 solenoids

  • Thread starter Thread starter FALKEN
  • Start date Start date
FALKEN

FALKEN

*************************
OK, while working on my tascam 32 today, the pinch solenoid died. I'm not sure why. I had previously cleaned it a few years back. I took it out and re-lubed it. I re-soldered the wires to the board. I de-oxited all of my connectors. still this solenoid does not move. when I press play, it should move so that the pinch comes in contact with the capstan. this is not happening. anyone have any idea how to proceed here?
 
Section 1-4 of your manual describes the operation of the brake and capstan solenoids. It might be nice to have a scope to check for the 200 mS 24 volt flashing current but a DVM will work for the 12 volt holding current.

Troubleshooting is a process of dividing a circuit in half looking for the point where coorect operation fails.

Looking at figure 1.5(B) (page 58) I see U519. It shows play in and play as two signals that you can test for. If play (pin 12) is high and the solenoids do not work then the solenoid circuit is bad. Otherwise the problem lies in U512 or the circuits that drive U519 pin 1(play in).

Does the brake solenoid actuate? If it does then we can deduce that play goes high and that the problem is with the capstan solenoid circuit.

When not in play (stop mode) the collectors of Q538 and Q541 should both be at or near 12 volts. When in play mode they should be at or about 0.6 volts. These transistors turn the solenoids on and off. If no 12 volts then you have a bad 12 volt supply or an open solenoid.

The cathodes of D515 and D516 should both be at about 12 volts. This should be true in any mode (play or stop) Their job is to short out the voltage spike that happens when you stop current to a solenoid coil.

When you enter play mode from stop you should be able to measure the 24 volt flashing current that is applied to the solenoids. It is there for only 1/5 of a second so you meter would not record 24 volts but rather something higher than 12 volts then settle down to 12 volts.This may be easy to see or hard depending on your meters reaction time. Of course a scope shows this quite nicely.

The flashing current causes the solenoid to actually move and the holding current keeps it actuated (more power to actuate than to stay actuated).

Hope this long winded post helps.

--Ethan
 
Thank you Ethan. I had to read your post about 10 times in order to understand it. :confused::o

Yes, the brake solenoid still works. Do you think that these transistors are on the main board or inside the solenoid?
 
FALKEN said:
Thank you Ethan. I had to read your post about 10 times in order to understand it. :confused::o

Yes, the brake solenoid still works. Do you think that these transistors are on the main board or inside the solenoid?
Click to expand...

That's good news. Because the brake and capstan solenoid share the same control signal ( play) and share the same flashing circuit and because the break works we know that yo have play and flashing.

This leaves the solenoid coil and the switching transistor as possible causes (along with mechanical problems).

Page 103 shows the transistors on the right side of the (as viewed on the manual page) Control PCB. I would check Q538 as noted in my prior post. It wold be useful to know if the solenoid coil was open (infinite resistance). You would just have to remove one of the wires from the PCB and measure it's resistance. It should be (oh say)5 ohms or so as a guess.

If the coil is OK and you have near 12 volts on the collector of Q538 and the solenoid is not binding mechanically I would then look at the base of Q538 for the control signal coming from Q537.

The signal chain is: Play goes high at pin 12 of U519 (should be near 5 volts). This then goes through D534to C544 and the unmarked resistor which creates a time delay so that the brake release before the capstan enguages when going into play. When pin 12 goes low (stop) the break activates first and the cap c544 discharges through R705 creating another time delay. This then lets the brake activete befor the capstan releases. D534 blocks C544 from discharging through U519.

From here forward the break and capstan circuits are the same with R615 doing the same duty as R618.

So when pin 12 is high (after the delay) the signal goes through R618 which turns on Q537 which turns on Q538 which allows current to flow through the solenoid coil.

You shold be able to compare loke points on the brake and capstan circuits and see where they are different. Different indicates a problem.

This should get you further along. A good visual inspection might show something. Also, you can ground Q538's collector which would then activate the capstan solenoid as a test of it's ability to work (thus ansewering the question : is it the solenoid or the circuit?)

Regards, Ethan
 
I can hear FALKEN counting up the readings now..."#1....#2...#3..." :D

Seriously, Ethan, thanks for being such a help on this forum...I don't think FALKEN could have even got this service from Teac back in the day...certainly not for free. You are appreciated.
 
You can always sell me your 32 FALKEN. Since it's in need of repair I'm prepared to pay rock bottom price. I've been wanting a 32 for about a year now but am a little short on $ Good luck with it.
 
I think it's Q538.

DEe5F.jpg



Looks like the trace came up. Do you think I can just soldier this back down or do I need to go buy a pen or something at radio shack?
 
some heat and a little extra soldier and it went back down. everything fixed! I even was able to adjust the motor speed pots to get it to exactly 7.5 and 15 ips! Well as close as I could get by matching a test tape to a digitally generated 1khz tone. Thanks ethan !! I would have never seen this if I hadn't been following the path you outlined. It was on a totally different area on the board and for some reason just didn't stick out (like trying to find waldo). Thanks again.
 
OK actually I lost the sync light and also the counter LED.........
 
Good news

Good to hear that you found the problem. You will be able to fix the lamp etc as well.

For a pulled trace like that I usually scrape some of the photomask off the trace and solder a wire along it and thus to the pad and lead. A little extra mechanical support.

Regards, ethan
 
well ive been messing with the counter and cant figure it out...here are some pics

g2rLe.jpg


hYWEe.jpg


do you see that white spot on the plastic? I think it was always there but now I'm not sure. Anyway, I can't seem to figure out whats wrong with it.
 
finally got the front frame open and got the sync light working... who knows what I broke in the process ! now just the LED and I should be in business....FWIW the machine still stops at zero, I just can't read the LED.
 
anyone know if the rec high eq is actually supposed to do anything?
 
Maybe it's a bad angle but isn't that little "tit" missing (like it broke off) from the top of the counter.:confused:
 
Well, there is a protruding little thing a top of the glass counter, which seems to be missing on yours. It's often recommended to be very careful not to brake it off while taking the front cover off. Maybe that's why the counter is not working?
 
That unit is a vacuum flourescent display. It needs vacuum inside to work. The "tit" he is talking about is the tube where the air is pumped out then heated to seal it. It normally comes to a point. I'll see if I can get a photo or an intact one.

--Ethan
 
Here is the photo

Here is what it should look like. The seal is in the cutout.
 

Attachments

  • display.webp
    display.webp
    27.7 KB · Views: 54
You must log in or register to reply here.
Back
Top