More Studer B67 work. Also, some insights on removing the PSU.

The power supply was already recapped, per the last post, but let me back up a little. Remember when I wrote about removing the power supply? Well, you can remove just the Stabilizer PCB. It’s held to transformer’s housing with two vertical screws that go through the PCB, and two more (horizontal screws) that attach the heat sink to the PSU’s housing. These are the two horizontal screws I’m talking about:


You can find the vertical ones yourself. The reason I bring this up is because there’s no reason to remove the whole PSU to just recap the Stabilizer board. More over, the PSU is heavy as shit, and if taking it was a pain in the ass, putting it back in the machine (when the Stabilizer is attached to it) is almost impossible. What threw me off when taking out the PSU initially was this connection:


The connection is the one you see in the center of the photograph.

The Stabilizer attached to it pretty tightly, and not being able to see the underside of the Stab. PCB, I couldn’t tell if it’s soldered or not. So yeah, it’s not soldered.

Reconnecting the cables required me digging into the manual and understanding the wiring lists. I’m glad I did that, because now I know more. But a good hint to which way the connectors should be oriented is that this machine is Swiss, and those dudes (using it as a unisex term) like things to be neat. In other words, the connectors are oriented so that you always see the flat panel and not the side that exposes the “teeth”.

Ok, enough about that. I put everything back in and tested the PSU unloaded. The +/-20V rails read a little higher, and the +24V rail read almost +30V. The -12V rail read -12V, so that’s good. The reason those other rails read high is because they’re unregulated and there was no load, so all cool there.

I connected the cabling, turned it on, and god damn it! The motors spin! I test the voltages, and the -12V rail is pulled to 0V. So now the problem is isolated to the transport board. I think (hope) that the transport chip is fine, because pressing the transport buttons, they try and do their job (solenoids are engaged, and some other things were happening). I hope that what happened is that some tantalum failed and shorts the -12V rail to ground. I’ll find out when I recap the transport.

Oh, I also finished cleaning and recapping the Stabilizer card. I need to figure out something with one of the -12V transistors there. More on that later.


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