Fostex G16 not recording or playing back audio

F

foleype

New member
Hi all,

I'm new here and am in dire need of help. I have a Fostex G16 (with Dolby C, not the Dolby S model) and I messed it up yesterday like the imbecile that I am. I tried to measure the master bias frequency on the J type connectors on the R/P cards ("measure the bias frequency at points J 2-7 per the manual), but I must have accidentally crossed the multimeter with the wrong connecting pins because I saw a little spark and when I put it back together, it no longer recorded or played any audio. The transport works great and the input monitoring functions are flawless, but it is silent when it comes to recording and/or playing anything back. I have a feeling it has to do with the mute line on the Connector PCB, but I am otherwise very lost. Can anyone lend a hand?

Here's a link to the service manual.
 
Simple things first - have you checked the fuses? I'd have thought losing power on the audio circuits would take out the monitoring as well, but it's worth trying. That manual doesn't seem to have a circuit diagram of the PSU, but that would be the first thing I'd check.
 
So I got channels 9-16 working last night when I crossed the 24v line with the J48 outermost pin on accident - if you look at page 83 of the manual I posted yesterday, you can see the schematic. Any idea what I did?!
 
Hello, this won't be much help but I have a Fostex VF-80 with exactly the same problem. On my input 1, if I record, the recording level signals that sound has been recorded but it won't playback. I have tried everything. Both the jack input as well as the three pronged plug for the mic, suffer the same problem - if I record, all readings are fine, no playback. I am currently looking for someplace to service what I think is a short somewhere, cannot find anyone who services Fostex equipment. Bummer - if you find a solution, let me know and I will do the same.
 
foleype said:
So I got channels 9-16 working last night when I crossed the 24v line with the J48 outermost pin on accident - if you look at page 83 of the manual I posted yesterday, you can see the schematic. Any idea what I did?!
Click to expand...

I was going to suggest bypassing NR to see if that makes any difference, but it seems to be a control pin on the a single NR chip rather than a true bypass system so I'm not sure it would make any difference.

AFAIK, depending on which pin of J48 was shorted, you'd either be going direct to ground - which will upset the PSU a bit but probably not much more - or send 24v through channel 13's input which may potentially blow out the NR chip for that channel, depending on what buffering there is between the I/O board and the channel card, and what the NR chip is rated at. I can't see any decent signal flow or system overviews in the documentation, so I have no idea.

What I do notice is that on the I/O connector board (p89) there are two chips - U2 and U3 which are 4052B multiplexors - given their link to the secondary CPU I would assume that it's using them to control each channel somehow.
What's significant to me is that this is the only place I can obviously see in the service manual where the channels are split into two banks of 8. U3 is connected to channels 9-16, U2 is handling 1-8. So if channels 1-8 are down, it might be worth investigating U3.

Unfortunately, I'm not sure how you'd go about testing it - I'm right at the limit of my understanding here and I can't quite understand what it's doing. Also, since shorting things out by accident seems to be a running theme in this thread, poking it about might be a very bad idea anyway since they're connected to the I/O processor. The 4052B is a standard off-the-shelf part. However, the CPU is custom and if THAT gets zapped with 24v, you'll be in the market for a new G16.
 
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