688 Track 7 dead

[telengard]

Went to record on my 688 tonight and track 7 isn't registering any input at all, from both mic and line inputs (with the appropriate scene for each). Other 7 tracks 1-6, and 8 are working fine.

Any ideas on where to start looking? I had this thing taken apart last year and I fixed and tuned up the deck, but I haven't dealt with the mixer section at all.

I'll start with a signal from my siggen going in and trace the audio, but given the routing is handled digitally, I'm not sure just how far I'll get.

Any suggestions, etc appreciated!

EDIT: the gain LED does light up with audio coming into the Mic input. If I crank the gain all the way up I can hear a very quiet portion of the audio coming in. EQ does seem to have an effect on this as well.

 

[telengard]

Answering my own post in the event anyone has a similar issue. I traced audio and it made it fine to the insert send. I saw that the faders were next. The track 7 fader is fine, but I moved around the 7/8 group fader (which I never use) and track 7 came to life!

Not sure why 8 would have been fine but not 7 though... odd.

 

[SkywaveTDR]

Maybe they route the signal through there or that it is mixed there somewhere. You would need to look at the block diagram to see the routing but as most people see these diagrams as useless they are still important to those not familiar with electronics components. Many Porta studio units have dirty selector switches and also broken jack inputs due to bad solder methods. The answer to the dirt issue is to cover Mixers and Porta studios with a towel or plastic sheet when not in use. That fuzz and dust will get into these over the years and is not always that easy to get out. Then when you do get to go inside these and disconnect connector and that you need to resolder joints on the headers and as it does not take much to crack a joint when it has a minimal of solder on them and then once you close the unit the new problem shows up. This kind of item made as the smaller units are is just as breakable as that wave solder no matter where it is put is not a very good manufacturing method- it may be fast and cheap but fails easily.