Tascam M512 / M520 Upgrades

So here's an update on this little project...

I was trying to cram and get at least a couple channel cards partially recapped and do a partial upgrade on the opamps before a tracking session last night...what a fiasco. :o

I got the cards done as noted above, but then when I put them back into the frame and hooked them up, things were wacky. the story ends okay, but I was calmly and quietly freaking out at first.

  1. None of the LED's on the modded channels worked
  2. There was a terrible hum on one of the channels...
  3. I was checking the other two channels in the 4-channel module that were unmodded and the eq section for one of the unmodded channels was feeding back on itself! :eek::eek::mad::mad::(

I discovered the humming was a shorted RCA cable in the ACCESS loop...pulled the cable and put the jumper in. Phew!

I then started checking other channel eq's and I found some others that were feeding back! I triple checked physical and electronic patch settings to see if I could explain the feedback phenomenon...nothing came of that. I disconnected the two modded channels from the rest of the module (power and bussing connections et al), and the problematic eq's were still acting up. Then I just pulled the module out completely. Eq problem still there! Well, don't understand it, but all the eq sections that were feeding back, I was able to resolve by rapidly sweeping the GAIN and FREQuency knobs for each of the three bands...dirty contacts??? Wierd!

Then for the channel LED's, duh, They're POLAR ya nimwit!" I says to myself...I didn't pay attention to how they went back in after I cleaned the contacts...funny thing is I put them all in backwards! :eek::D

So everything is okay now, but I didn't have the module back in last night to see how things worked at the tracking session. Oh well...There will be another in a couple weeks.

I was hoping the noise level would be improved with the cap replaced that I've done so far...there may be a little improvement, but not much really to speak of...I guess that's not too suprising because only 6 caps have been replaced on each channel card. :rolleyes::o

I will say though that the techniques I used for cleaning the pots this time around (thoughts I supposed in this thread...) worked very well.

ASSIGN switches for PGM groups 1, 3, 5, and 7 don't work for one of the modded channels. :mad:

Wait...PGM group #1 doesn't work at all! :eek:
And arg!

I wish I could make sense of why they used the opamps they used where they used them!

I mean, they put the 2041's in the Balance Amp driving up to +8dBu loads...I'd expect them to put the heavy hitter in there (the 455x)...then they used the 455x in the TAPE input path...I was thinking that, since the likes of the OPA2134 can drive +30mA loads then it should be fine wherever the 2041's and the TL072's reside...but the 455x...I wish I knew how to figure out schematically what the potential current demand is on the 455x chips, especially U7 (that's the one where it is potentially driving a bajillion things...) :mad::(:confused:
Hi Everyone, I just joined this forum, anyway, yesterday one of my best friends dropped-off an old 80's Tascam M-520 20 Ch analog studio mixing desk, plus the rackmount power supply, that he gave me....for nothing, I'm going to be doing some restoration-work on it so I can use it in my little music studio I set-up in a spare bedroom in my flat, here's a pic of the desk all set up in my studio room.


  • Tascam Mixer_2_resized.jpg
    Tascam Mixer_2_resized.jpg
    195.7 KB · Views: 1