More Studer work today. I tested the voltages that IC1 on the Tape Transport Control board outputs (pins 1 and 7) and they seem fine according to my Studer friend. These are DC voltages and they measured around -2 to -3 V when the appropriate little roller is DOWN and about 11.34V when the little roller was held UP.

Also, following my friend’s recommendation, I checked that the motors are getting enough juice (about 100VAC) from the power transformer’s secondaries. They are!

I think it’s some logic thing that’s messed up somewhere because it’s always only one motor that’s being responsive, and rolling the big, right-hand roller will cause the supply motor to stop running and turn on the take up motor.

Weird stuff. I need to really delve into the manual and understand what each voltage does.

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I’ve been a little quiet because I was waiting for an order of parts and concentrating on studying. Anyway, I got the parts – SN74LS02 and sockets to replace IC8 following the advice of my Studer friend. Unfortunately, the problem is still there. Only one motor is running when I turn the machine on.

This one is a head scratcher! Yeesh!

Guitar recording

This might not be helpful to anyone who reads this but me.

Recorded guitar today. Guild S-300D into an Orange Tiny Terror into a 1×12″ ported cab (similar to TL806).

I used a Coles 4038 going straight into my little sound interface’s preamp (Avid one track thing).

I aimed it pretty much at the center of the speaker, and at a foot away it picked up too much of my picking and sounded a little thin (I wasn’t playing loud). At about 8″ away it was a little too boomy. Will try 10″ away next time.

UPDATE January 8th, 2015:

Same setup again (all of it). I kept the microphone 10″ away from the amp and I got the same sound. At 10″ away there’s already a lot of bass because of the proximity effect. It’s not a bad sound, might even be a good sound, but it doesn’t sound exactly like what I’m hearing in the room. I should mention, though, that I play quiet enough that I can hear the acoustic sound of the guitar along with the amp. That could contribute to why it doesn’t sound the same. Anyway, I moved the microphone maybe an inch or two away from the center (off-axis) and things cleared out a little more. Not as boomy anymore. That’s something to keep in mind.

More Studer B67 work trying to figure out what’s going on.

I don’t remember what prompted me to do that, but I decided to turn the right hand roller guide by hand when the supply motor is the responsive one. Turns out, it turns off the supply motor and turns on the take up motor.

My friend instructed me to test the MOVE voltage at the right sensor PCB.

I taped both tape lifters in the UP position (to trick the machine that there’s there’s tape threaded, I believe). Then I checked the voltage between J1-2 and J1-1 in these different scenarios:

Pressing PLAY and turning the roller by hand:  +4.78 VDC.
Machine in STOP and turning roller by hand: +4.78 VDC.Machine in STOP and roller is still: +0.03 VDC.

FIY these three voltages are what should be expected (essentially +5VDC when there’s tape “moving” and 0 VDC when no tape is moving).

Then I turned to checking the voltages on IC8 on the transport board. This is a pain because I had to remove the transport again.

All voltages are with respect to pin 7 which is ground.

Pin 6 was constantly at -0.53V regardless of the machine being in PLAY, STOP, and the roller spinning or still.

In STOP mode, pin 4 measured 4.31 VDC when the roller was spinning and 0.12 VDC when the roller was still.

In PLAY it dips to 0.12 VDC and quickly goes up to 4.23 VDC (roller not spinning). Spinning the roller makes it go down to 0.12 VDC.

Still not sure what this all means. I’ll update when I do!

Studer B67 running/spinning motor problem – fixed!

Straight to the point: The casing of the take up motor’s power transistor was making contact with the top chassis. I uninstalled it off, and there was a piece of fuzz on one of the transistor’s legs going all the way up to the casing. I cleaned it up, reinstalled the transistor, tested that there’s no continuity between the transistor’s casing and the chassis, and turned the machine on. The motor wasn’t spinning anymore! Can’t say if it was the fuzz that caused it, but reseating the transistor fixed it.

So how did I arrive at that? I’m not yet fully proficient in electronics, so what’s following here might be incorrect, but my prodding and testing was guided by my friend who’s a Studer tech, so maybe not!

Anyway, in my last post I detailed the measurements I took on both motor control boards. The readings on the supply board are normal, the readings on the take up board weren’t, particularly, the voltage between pins 5 and 10. On the other hand, the voltage on pins 7 and 10 was within the tolerances of what would come from the transport, so that reduced the problem to a short that happens somewhere around the motor (as opposed to the transport). I started checking for continuity at the transistor socket, and I noticed something peculiar. On the take up board, I had perfect continuity between pins 5 and both the transistor’s casing and the chassis. Same thing with pin 6. Pin 5 is the collector and 6 is the emitter, and it didn’t make sense that they should be at the same voltage. Also, that’s not what I got for those pins on the supply motor’s board. My friend suggested to check if the casing of the transistor is touching the chassis, and that was it.

I should mention, however, that now there’s a different anomaly. I turned the machine on and followed the manual’s initial checkout procedure (p. 2/17, section 2.6). When I pressed play, and only the take up motor was responsive. I turned off the machine, tested some connections on the supply board, turned the machine on, and now the supply was responsive but not the take up. Turned it off again, tested some connections on the take up, turned it on, and now the take up is running and not the supply. What the hell? Hopefully this one will be easier to chase down.

Voltage measurements on a Studer B67’s motor control boards

The motor control boards are the little ones that have the Rifa capacitors that are known to leak. I wrote about recapping these here.

My friend who’s been helping me figure out what’s wrong with this machine told me to take some voltage measurements on the motor control boards, so I did. I still don’t know what they mean, but I will soon. For future reference (for my own sake and others’), here is what I measured:

Take up motor control board:

Points 3 & 4: 107.7 VAC
Points 4 & 2: 107.6 VAC
Points 4 & 1: 188 VAC
Points 5 & 10: 0.30 VDC
Points 6 & 10: -0.012 VDC
Points 7 & 10: .042 VDC
Points 12 & 14: 189.8 VAC
Points 11 & 13: 106 VAC

I think the voltage between points 5 and 10 is a problem, because it’s deviating from the supply motor voltages, but also I was told it should be high DC voltage.

Supply motor control board:
Points 3 & 4: 100.2 VAC
Points 4 & 2: 100.3 VAC
Points 4 & 1: 95.4 VAC
Points 5 & 10: 139.2 VDC
Points 6 & 10: 0 VDC (this one was exactly zero)
Points 7 & 10: 0.0 VDC (Again, on the nose).
Points 12 & 14: 6.8 VAC
Points 11 & 13: 4.5 VAC

The voltages between points 12 & 14 and 11 & 13 differ, but I think that’s because the take up motor is running at full speed.

I think I’m getting close! I will update this post with what should be the correct voltages when I know them. EDIT: the correct voltages are what showed up on the supply board.