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-   -   Sony Microcassette M330 overheating (https://www.vintage-radio.net/forum/showthread.php?t=197560)

IanNVJ35 17th Jan 2023 6:39 pm

Sony Microcassette M330 overheating
 
I am having a go at fixing this little machine for an older lady who wishes to play her old micro-cassette collection.

I somehow feel it's a bit beyond me as it's all surface mount and no manual but I have the fault of seemingly no operation, so I tried on my bench PSU. I see that the Voltage (3) is dragged down to around 2 at 500mA limit with the power amp IC getting hot.

Nothing operates nor does the motor turn.

It's this one. https://www.nisshinbo-microdevices.c.../NJM2073_E.pdf

I checked if it was short internally - it isn't. I checked if the output was shorted - again, it isn't. There was some heavy brown flux on the trace side of the PCB around many of the solder joints which I cleaned off leaving an odd remnant of white gummy stains. I'm wondering if components may have been damaged by this.

Thanks for any ideas. If I can't fix it I will just return to her but I want to try.

ben 21st Jan 2023 12:42 am

Re: Sony Microcassette M330 overheating
 
The problem is likely very near the power input. Short in a dc socket? Probably simpler to pick up another one online, they're cheap enough.

knobtwiddler 21st Jan 2023 12:02 pm

Re: Sony Microcassette M330 overheating
 
Does it contain tants or types of caps that can fail short circuit?

MLCCs, especially SMT types, can fail this way.

G6ONEDave 21st Jan 2023 12:26 pm

Re: Sony Microcassette M330 overheating
 
I have the paper service manual for this model that I could scan and email to you. If it's of any help PM me with your email and I'll get it scanned in the next couple of days.

Dave

IanNVJ35 21st Jan 2023 1:10 pm

Re: Sony Microcassette M330 overheating
 
Thanks for the input. I checked for tants but only a few electrolytic ones which read OK.

I'm actually running from the battery supply with flying leads. This evening I will lift the DC input leg on the amp - see if that helps.

Dave, the service manual would be appreciated. I'll pm you.

Yes I thought straight away of suggesting a working replacement but I'd at least like to try. I'm interested in what could be wrong.


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