Electronics > Repair
Power supply board damage - reversed polarity on two CONs
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vladc77:
Yes, all my previous testing was done with all connectors unplugged from other boards. I tested the reel motor with a 9v supply. It works well. I localized my investigation fully to the power board supply.

12v could be loaded into the power board supply from the logic board. I assume pop polarized caps should be only on the PSU board. Correct? Is that possible to correct the polarization of the caps?

At the same time, there are not many caps there. I believe I tested most of them. All connectors except CN-5 pins get proper voltage. I hope I am not missing anything here.

With all that said, I am wondering if there are any other ideas on why CN-5p2 and CN-5p3 may not be getting the voltage as needed while this voltage is available for CN-6 pins. Thank you again!
vladc77:
MathWizard, I took your advice to forget the schematics and make my own. Thank you!

I decided to trace the source which is receiving +5.6v from the CN-5p2 in the logic board of this Nakamichi. I was surprised to learn that this area is working on +12v voltage. The values indicated in the schematic are just not correct. I am puzzled how this could happen, especially from this top-end manufacturer as Nakamichi. Based on the schematic, I was tracing something that did not exist. The power supply was working correctly all the time. It was a bit of bad luck I connected two connectors incorrectly with one of them had incorrect values listed in the schematic. I was 100% sure something was damaged.

As soon as I realized that, I got a few ideas about what could cause the deck not doing FF, Rewind, and Play. The first idea was a low-hanging fruit option to replace burned light bulbs in the transport that is supposed to provide light for the inside cassette compartment. It looks more like a decorative thing but it is not as I learned now. There are two photosensors there. I thought this light was the only source of stable light for them to operate. As as soon as I replaced the bulb, everything started to work. In the end, it was a relatively easy fix. However, I think the design using the photosensors with that bulb is not the brightest idea. That bulb is not reliable. As soon as it is gone, the deck is gone too.

The only remaining issue is auto-calibration which does not pass on the tapes I have. The rest seems to be working well.
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