3M M79 problem...help

[plateson]

i suppose that may be what i have to do, i just wish i knew that was it for sure, you know? not that shipping a card like that would be costly but shipping multiple things at different times trying to troubleshoot the problem could get to be costly. i will call doug weeks on monday though and see if he thinks that would be the problem also. then i'll probably ship it out for repair :?

in the meantime any other ideas you have are greatly appreciated. i know a guy about an hour away, maybe he'd bring his card over and let me try the machine with his in and see if that fixes the prob. i'll update later. thanks again.

 

[fazeka]

[quote author="plateson"]not that shipping a card like that would be costly but shipping multiple things at different times trying to troubleshoot the problem could get to be costly[/quote]

<sigh> That's exactly why you need to call Doug, fer cryinoutloud! :?

 

[plateson]

i shot doug an email and so, now i wait to hear the news...

 

[plateson]

talked with doug yesterday. here's the latest. he told me to try a test to see if the recording cards (at least one) had started to malfunction. he told me to:

"try pulling the audio cards out, except for lets say track 2
and 23 (or 2 & 15) , and then see if the problem exists. If it does not,
then logic on one of your cards has failed and is keeping the master line at
a false state. Start reinserting cards until the problem reappears, and then
you will have found the card with the failure."

I tried this, but it didn't help. so, when he and i talked again he said it could be:

"this is being caused by a
translational logic error in the mode switching circuitry on the transport
logic board."

he is going to give me a few tests to do on the logic card and depending on the results i may be shipping it off to be fixed. that's the latest, still more to come... :roll:

 

[hitchhiker]

hey Brett!

Thanks for the update, Good to know about that initial test. Keep us posted. :thumb:

Lance

 

[enthalpystudios]

yeah, please do... i just got a 'project' m79.... if it takes me a couple years to get her going i'll live, but i think it wont be so bad as that.

anyway, i'm very interested to hear how things go. i'll probably be calling mr weeks depending on where my logic runs out ;]

 

[plateson]

well, we trouble shot the deck over the phone and as you would expect when you are dealing with an expert on the machine, he was pretty right on with his assessment. it kind of works like this, he told me where to place the multimeter leads and we found...

in a non moving state, transport armed, the multimeter read .4 volts.

in record it read 28v.

in cue mode we still had 28v. according to the schematics and manual it should be 15v.

i was unaware of this type of electronic style but apparently as he described it, the machine knows what to do and switches modes, not in an on/off sort of way but in an on+how much electricity is passing thru sort of way. and it appears that my logic card is confused and not sending the right amount of electricity thru at the right time. could be transistors or diodes or a microchip on the logic card. so now fedex has my card and they will be delivering it to mr. weeks on monday.

i'll post more as the DRAMA unfolds...

 

[hitchhiker]

[quote author="hitchhiker"]well I'm no expert on these matters but i do own an M56 and i think they have much in common. My manual and schematics say that the sync mode gets 5 volts DC to trigger the sync relay but not the record relay.If set to record on that chan it would get the full 28 volts.
I would pull the main logic board and test diodes and transistors (IC's too) for shorts.


Lance[/quote]

On the M56 it's 5v and 28v instead of 15v and 28v. Do you have a signal block diagram schematic showing all the relays ,head windings ,card # etc? If so you it would be agood thing to make a study of. It could help you fix other issues one day.

thanks for the update.

 

[fazeka]

Told ya Doug was the man! :grin:

 

[myface]

Hello,
I've just recently aquired a 3m M79. Everything seems to be working except for one thing. When I have already recorded a track and want to lay down a second track while monitoring the first track, the first track I recorded gets erased. It's like the record head for that channel isn't switching to the monitor only mode. Could this be a logic disorder? I have troubleshooted the remote transport and it seems to be arming the tracks fine and functioning. I borrowed another remote and patch cords from a spare machine I have and it does the same thing. I have also tried recording to different tracks but to no avail. It records the track down fine but when I go to put another track down while monitoring the first track gets recorded over and blanked.
Any suggestions? I appreciate any ideas from any level of experience you may have with this infamously troublesome but beautiful sounding machine.

Thanks!

Brett

Switch Audio Card with another one and you will probably see the problem travels with the card