Serviced Teac 80-8 with Incessant Intermittent Volume Drop on All Channels-No Rhyme or Reason

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xynox

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Let me start out by saying that I know this is an old machine and maybe someday I'll get something else, but this is what I have to work with ATM.

Recently purchased a Teac 80-8 from a reputable reel to reel dealer that had been serviced and bench tested and even came with frequency diagrams for each head(or maybe for each channel, can't quite remember).
Pretty much ever since I got it I've been having the insanely frustrating issue of when tracking, upon playback or using the monitor head there are sudden volume drops-then sometimes it'll return, then maybe slowly fade, then maybe come back full force, then maybe cut out all together, then come back slightly, then maybe come back all the way on EVERY channel.
There is no rhyme or reason. Sometimes I think I've got a channel that's working and then it cuts out.
Input and Norm settings sound great- so the machine is getting good signal, but it won't lay track properly.
I've tried swapping cards and it actually seemed to help on one of the swapped channels...but then I was unable to monitor the channel during recording-like it was totally silent- but then on playback the channel had tracked and I was able to listen to it on both record head and monitor head. How is that physically possible?wtf
Knocking on the cards and/or relays seems to have no effect on the volume drop issue.
I've cleaned all the RCA connectors on each card with deoxit as well as the edges that plug into the machine.
Here's a video of one input feeding all 8 channels at a time so you can get an idea of what I'm talking about.

guitars a bit loud-might want to turn it down some

another one

here's one of just two channels playing the same input


and then after using it for a frustrating period of time it seems to start to get better and the channels want to work but they seem to revert back to their old ways once I've given the machine a break for a while.

Now I'm concerned I'm pushing my 40 year old transport too hard trying to diagnose with ridiculous issue.
 
Hi.

Don’t discredit the machine because it’s not working right and it’s “old.” Yes the 80-8 is a less “sophisticated” machine, but that also means it’s potentially easier to fix and keep operating long-term than a machine with, for instance, a complex full servo transport. The 80-8 was a home-run for Teac because of its reliability and good sound…and price at the time. It’s a solid machine. Question: this diminished level issue…are you saying the level changes identically and simultaneously across all tracks, or would you instead describe it as random in nature, no rhyme or reason and dissimilar between tracks? Like you think you have something figured out with some manner of consistency swapping cards or whatever and then it curve-balls you again and you’re left saying WTH…is it like that?
 
Yes, its the no rhyme no reason thing. Here's a video first showing levels on input mode and then monitor of one input feeding all 8 channels:

You can see how out of whack thing get. There are more videos in the OP
he's never seen anything like it before and is going to send me 8 new cards when he can but I'm not convinced its the cards.
I do love this machine and really just want it to work properly.
 
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First thing I would do is replace all the relays. I’m surprised your tech has not experienced anything like this before. I’ve experienced this exact symptom set on multiple machines. The problem was faulty relays. That’s where I would start if it was me. I may be completely wrong.
 
I'm not a tape man, but is the power rail to the channels fluctuating?
 
my boy is sending me 8 new tested hard cards and looking into relay alternatives. Will update.
 
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