Porta02 input issue

[Handpanther]

Heya! I have a Porta02 mkII and all 4 channels playback as they should, and the input on channel 2 works fine. Channel 1, however, is dead - no input audio (on 1 or 3), no LED response. I cannot find anything visually the matter on either PCB, and the connecting cables all look intact. Where should I focus my attention to narrow down the fault finding?

Thank you!

 

[Handpanther]

This is a tape machine from 1999. It doesn't have firmware.

I am asking in a DIY repair forum, which would imply an inclination to repair it myself.

 

[Jack Saturn]

Have you traced the signal path on channel 1 to see if the audio signal stops at a certain point? Focus on the capacitors in that path and you should be able to find the problem.

Alternately, have you confirmed that the solder joints for input jack 1 aren't broken?

 

[Handpanther]

I've traced it only visually, mostly because I don't know yet how to do it with a multimeter. I suppose now would be a great time to learn

The solder points on the jack appear fine, and I was initially reluctant to desolder it to check/replace mostly because I didn't want to risk adding another fault.

Thanks for the reply!

 

[Jack Saturn]

I've worked on a lot of Porta02 machines, and usually when there's a problem like you describe, it's a failed capacitor, and not generally one that's obvious to the naked eye. Keep us posted on what you discover!

 

[Handpanther]

I built a probe based on the one Tetrakan used in his video about signal tracing, and the last place I get signal is the top pin of the slider pot. The pot itself doesn't show any damage, so I'm going to desolder it, check it, then put it back in and see what that does.

 

[Jack Saturn]

It could be that the slide potentiometer itself has failed, likely because of damage to the fader track. Sometimes it's not even visible to the naked eye. If you're able, disassemble the fader, clean it, and make sure there's no gunk on the teeth of the wiper, then test it again with a multimeter or the audio probe.