Tascam 488mkii question about ground to Mr Capstan

[DrGonz78]

So I decided it would be fun to pull out the old tape machine and get her going. So far we have a new belt and a C-Gear. Usual suspects so they claim but no dice for me. I observe some turn on spin of the capstan belt and then it dies after a second. I removed the motor from the circuit and put a 12v supply on it and it made that noisy brushless sound. So I then measured the wires feeding the motor and I don’t see 12 volts.

Looking on the main power board there is U1 which will have 5v supply on one side and 12v on the other. All check out and then I probe for 12v on the Controller board. This time I see 12v!! However this is with my black lead grounded directly to the power board. If I back probe the socket with black probe on negative side of the Capstan motor I get 0vdc and a strange trickle of about 2-3vac registering on my meter. Okay that’s basically what occurred.

My question about all that involves Q9 and how the negative side of the Capstan connects to reach ground. So I will post that part of the circuit and the schematic too. I think page 57 & 58 of the schematic shows the control board and scroll up to see power board. Very hard to read schematic. But what is Q9 doing in the circuit? I will double check the wire again but not sure the ground connection is due to this transistor.

[DrGonz78]

Oh I can’t upload the whole schematic since it is like 15 mb. But here’s a link. Well my file says it is 15 mb but the link thing says 5mb. Who knows.

[g1]

You are engaging the "tape inserted" switch?

[g1]

Further to that, I think the "casette" (tape inserted) switch sends signal to the micro which in turn tells Q9 to ground the capstan motor.
Cassette switch is top right of control board schem.

[DrGonz78]

Correct on all accounts G1 thanks. I forgot to insert a tape and actually something got bent that was preventing it from working. It was easy to bend it back to fit and that got Q9 grounding the fan. The behavior of the capstan motor at turn on is that it spins a second then resistance drops on the emitter of Q9 and then the 12v engages. That was not happening before and I know that I inserted a tape several different times. It must have been the tape cassette sensor was bent out of shape. Thanks again G1 it’s spinning great now. Next issue is getting transport to engage.

The tactile switches on this thing are the ones that don’t really hold up well over time. Just like all the ones I have had to replace in effect pedal boards.

[DrGonz78]

Further to that, I think the "casette" (tape inserted) switch sends signal to the micro which in turn tells Q9 to ground the capstan motor.
Cassette switch is top right of control board schem.

It definitely helps if there is an inrush of current when turning on. Stabilize the power rail then turn on the very sensitive motors.

Well must be my lucky day. The transport is active and it’s ALIVE!!! Should be fun going through tapes I recorded over twenty years ago. I think I will give the gears a little more silicon. Only thing noticeable is that rewind is sluggish compared to ffwd or play.