Nakamichi TA3A intermittent power cycling

[TightMids]

Hi everyone! first post here

A friend of mine gave me his broken Nakamichi TA3A (stuck in protection mode), and I fixed it by replacing the appropriate resistors with higher capacity units. All was well and it worked like a champ (the sound is amazing!!) for a few months - but now I'm having a different problem.

At completely random times, the amp will power off - and nothing you can do will turn it back on. All you can do is sit and wait for it to decide to switch back on. It usually takes only about a minute, but sometimes it takes hours, one time it took an entire day.

My first thought was, maybe a fuse? maybe something got knocked around when I made the repair? I'm not an electrical engineer but I'm pretty good with a soldering iron.

Any ideas? I love the sound of this amp, and I'm not really in a financial state to drop serious dough on another unit...

Thank you for your time!

 

[powerflux]

my guess is simply worn-out capacitors.

 

[TightMids]

my guess is simply worn-out capacitors.

thanks for the tip, is that something I could do myself or would you consider the amp 'too far gone' in that case? How would I troubleshoot which capacitors needed replacing? aside from overhauling all of them

 

[powerflux]

can you make a few internal photos? that way we can identify the 'hot zones' and point out components that will have aged more than others in the more 'cool zones'.

i expect a few discrete regulators with hot pass transistors where the solder can be cracked + close mounted capacitors that may be your problem and are worth it to be replaced anyway.

the problem could however originate at the protection circuit where the turn-on timing capacitor is dying. Still, those 'hot' capacitors must be renewed too to fully enjoy the amplifier for the next 10 years.

 

[TightMids]

cool, yes I'll take it apart on Saturday and take a bunch of pictures. Also, while I have everything set up I may as well replace everything I can; would love to get another 10 years out of this! Thanks again.

 

[TightMids]

I just had a thought...

Could the resistors I replaced in the protection circuit cause this? Maybe the solder broke and it's having a hard time completing the circuit? Or would that cause a separate problem?

I guess I won't know until I open it up anyway, just getting anxious sitting here at work thinking about it

 

[powerflux]

that could certainly be the cause. those original resistors were chosen for the application. over-dimensioning isn't repairing the root problem, but fixing the symptoms. there might be previously hidden faults emerging now.