Otari MTR-10 2 PSU HELP

Hello Everyone,

I recently picked up this tape machine from a radio station that was selling a bunch of older machines that were no longer in use.

When I bought it, they said it had a bad winding on the transformer, but upon my further inspection, I have determined that it has another problem. I tested the voltage at pins 8-1 and 8-2 on the linked schematic, and I got 10.3 volts(even though the schem says it should be 9.5VAC). It also shows that this winding lights the VU Lamps and those light when the unit is powered on. So the problem is located somewhere else in the circuit.

The symptoms of the problem are a lack of +10VDC and +5VDC at the connectors. The guy I bought it from said that they used a bench supply to power the +5V and it was working, so I assume that the problem is in the section I've highlighted on the following schematic.

http://fucanay.fischerworks.com/schems/otari_psu_schem.gif (1.9M)

The circuit has an ICs (though I haven't actually been able to find it on the board), a couple of large caps, a couple of transistors, several diodes(rectifiers?), and various other resistors and small caps. Nothing too special to me, just by looking at it.

Could somebody look at this schematic and tell me what the likely culprit could be? Is there a preferred way to trace down a problem in a PSU?

I'll answer any questions to the best of my ability, though this is the first PSU I've dealt with.

Thanks in advance

Matt

Trace the pcb from the incoming ac voltage and untill the rectifier(s). Check that you have approximately correct dc after the rectifier (1.4xVac) - that is, at the first larg'ish electrolytic after the rectifier.

If you don't get DC voltage, replace rectifier(s)..

Jakob E.

[quote author="gyraf"]Trace the pcb from the incoming ac voltage and untill the rectifier(s). Check that you have approximately correct dc after the rectifier (1.4xVac) - that is, at the first larg'ish electrolytic after the rectifier.

If you don't get DC voltage, replace rectifier(s)..

Jakob E.[/quote]

So would I just find the positive side of C4 and hook up my multi-meter to that and ground? I'm so new at this that I probably shouldn't even be messing with stuff this complex, but if you guys don't mind me asking stupid questions, I think I can do this and learn a lot in the process.

Thanks

Matt

HAHAHAHAHAHAHA!

I love my life. While tracing the pcb I found some broken solder points on several connectors that hooked to the transformer. Re-soldered them all. All done. Power supply works as expected.

Fully functional Otari MTR-10 2 for $50!

Thanks to all who have advised me through the forums and PMs.

Matt