Trying to revive my multitracking rig. It’s a MOTU HD192 which I might sell or just keep using. Still haven’t decided. Anyway, mine had a noisy fan like most of them, so a while back I bought a new fan to replace it. Today I finally put it in.

I followed the internet’s advice as far as the size and got a 5cm x 5cm fan, and it’s a little too big I think, so it’s held in place with only three screws. The original screws were lost ages ago, so I had MOTU send me some because I couldn’t find the right ones at the hardware stores. These are 4-40 because I was able to find the right nuts at the hardware store. Go figure. By the way, MOTU’s support guy was very nice and helpful.

In the process of taking apart the chassis I accidentally broke the WORD IN (not SYSTEM WORD) connection and had to re-solder it.

I’ve been working on a quite a few other projects but been bad about writing up about them. I will have more time now that school’s out for summer.

Update on the Studer B67.

I believe I mentioned before that I isolated the problem to the counter board. I don’t know anymore if that’s true, but by probing around it, I realized that the flip-flop comprised of IC3 isn’t flipping or flopping. From all the probing, my understanding of the schematic, and the help of online friends I realized that the tape sensor is in charge of of activating the flip-flop. When the roller turns one way the flip-flop latches in one position, and when it turns the other it latches in the other position.

The manual states that QP-DIR1 and QP-DIR2 are approximately 90 degrees apart, and I realized that depending on the direction of rotation, either signal should be leading. What I was seeing instead is that QP-DIR1 was always leading.

I pulled out the sensor board and powered it with my bench supply. I got 0V  at QP-DIR2 (R13), which is weird because I was seeing it at the counter board. So I went probing around the phototransistor (DLQ2). At the collector the voltage was swinging between 4V and 5V, DLQ1 was reading similarly.

DLQ2’s emitter is connected to ground through a trimpot and also to the base of Q5. So I checked the measurement at the base. I was seeing 0V. I tested the trimpot and it was basically shorted to ground. I figured it’s bad so I pulled it out. I tested it outside the circuit and it worked fine. I put it back in, and same thing. I paused and thought for a bit, and realized that it’s possible that the base-emitter junction is short and that’s why the trimpot was reading 0 ohms. I pulled the transistor out and bingo! That junction is short (as well as the collector-base junction). Surprisingly, I have a few BC237Bs on hand, so I put one in.

Since I had the board out, I replaced C2, a 10uF 25V Frako. Since it’ll go short one day, now is a good time to replace it (and I had a replacement).

I also cleaned the board and the weird yellow residue that was on the roller, so now it’s ready for the new rubber ring I got a few months ago.

I installed the sensor back in the machine and now the flip-flop works as intended. With the roller turning CCW IC3 pin 6 is HIGH and pin 3 is LOW. Turning it clockwise makes IC3 pin 6 go LOW and pin 3 HIGH. Good.

However, the problem of just one motor spinning isn’t gone yet. Now what happens is that one motor spins when I pressed PLAY/FF/RW, but turning the roller in the appropriate direction turns on the other motor and turns off the first. So for instance, if the supply is working and I turn the roller clockwise, the take up will start running and the supply will slow down to a stop. Similarly if the take up is running and I turn the roller CCW. In this case the supply will start running and the take up will slow down.

The trimpots (R10 and R19) control the duty cycle! I have to figure out how to adjust them to get 50% duty cycle.