Studer B67 recap: Part I

Started the B67 recap today. A bit of background first:

I think I mentioned it before, but this machine’s biggest problem is that as soon as it’s turned on, all three motors spin and nothing can stop them other than turning the machine off. Each motor (supply, capstan, takeup) on this machine has a little control board that “mixes” the AC current from the motor and DC current from the Transport to create a constant torque. Honestly, I’m just parroting what I was told here. Anyway, these motors control boards have suppression capacitors, made by Rifa, and being old and also kind of crappy, they fail and short, and when that happens the motors spin like I described above. So first order of business was to replace those.

Supply motor control PCB

Before: supply motor control PCB.

Rifa caps. See those cracks? Those mean the capacitors are on their way to Valhalla/already there

Rifa caps. See those cracks? Those mean the capacitors are on their way to Valhalla/already there.

New, modern capacitors.

New, modern capacitors.

Turned the machine on, and the motors still spin. Bummer, but I didn’t expect this to be an easy fix. Not knowing if I somehow botched the things in the recap or not, I remembered reading that it’s possible to disconnect the motor control PCBs from the transport and thus isolate the problem to either the transport or motor controls. Here’s where I read that. So I did that and the motors stopped spinning.

So the problem is at the transport. This is a good thing, because it means I didn’t mess anything on the control boards, but on the other hand, the problem could be a dead IC in the transport, and those are said to be rare and expensive. There’s one on eBay UK right now for ~$69.

I’m thinking what I should recap next. At first I thought it should be the transport, because the problem is most likely there, but then I thought about it a little more, and if something is messed up at the PSU, then the whole machine will be out of whack. I don’t know if PSU failure would manifest itself by freaking out the motors, though.

FWIW, I don’t think the Rifa caps on my machine were bad. Usually when they die they let out a lot of smoke, and I saw no signs of that. However, it’s good that I got rid of them because they’re a ticking time bomb.


One thought on “Studer B67 recap: Part I

  1. Pingback: Voltage measurements on a Studer B67’s motor control boards | Fixing and Building

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