Author Topic: Help with schematic voltages  (Read 6819 times)

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Offline mij59

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Re: Help with schematic voltages
« Reply #25 on: September 05, 2014, 06:34:05 am »
Thanks for sharing.

Please describe the malfunctioning .
Do you know how to operate the unit ?
Please post photo's of the boards.

You could start by checking the power supply voltages, it think the +15V and -15V are present, how about the +5V rail ?
Check the backup battery.
Take a look at the block diagram in the manual .

I do know how to operate it as I've had about 5 of these units through the years. I have 3 of them now. Two are malfunctioning and one works. I bought this particular unit as NOS. It had been sitting on the shelf NIB since 1986. I turned it on and it ran for 15 minutes then there was a small pop and the audio cut out. I power cycled it and the direct audio came back but no effect sound can be heard.

So far I have checked all voltages mentioned in the service manual. They are all correct at the test points. I additionally checked voltages a few places around the circuit and compared them to the schematic. They seem fine except for that mentioned in my OP. The backup battery voltage is fine. I measured a bunch of caps with an ESR meter and they all seem fine so far. Mostly the power supply caps but we know that is working. I haven't actually done a whole lot of trouble shooting yet as I don't have a lot of time. I have hopes that when I hook up my scope and function gen and look around the test points I will narrow down where the anomaly is.

I've attached a pic if anybody is interested. These things were very expensive high end studio stuff back in the day. Built really well. I've only ever found one bad cap in any of them yet. I think they are Nippon Chemicon but not sure. Also FYI the gunk you see around the base of some caps is old glue from the factory.

Since the unit is quiet old check for mechanical issues like bad solder joints, connectors, switches, etc.

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