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RT 707 Source monitor no longer working

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dnesseth

New Member
I am new to this forum so apologies if I misunderstand if this is not the correct place to ask this question.
I recently purchased a Pioneer RT 707 tape drive in very good condition. There was an issue in that it had no audio.
All other features with tape motion, tape rewind, etc worked great.

First, I replaced the electrolytic caps in the following boards using a kit purchased on EBAY
  • Playback Amp
  • Power and Oscillation Assembly
  • Head Amp assemblies
  • Mic Amp Assembly.
There was still no audio (everything else such as tape movement continued to work OK).
With some digging, an oscilloscope and help from this forum, located and replaced Power Transistor Q 307 and resistor R306 and the unit's audio came to life.
It was working great with both play and record.
Ended up replacing the counter belt and directional lights which was the last thing to fix.

Yesterday I put the covers back on and everything is still working except that the Monitor audio would play at a barely audible level with Line Recording level set at max.
This was with the tape player in source monitor mode meaning that recording was not active at the time.
  1. Normal play works OK.
  2. Just selecting play (hubs spinning and without a tape being mounted), enables the source monitor to work OK.
  3. Normal record works OK and the monitor audio (monitor switch set either to tape or source) works at normal volume while recording.
  4. This issue affects both right and left channels.
I have been troubleshooting this all morning without success.

The only thing that I've come up with so far is that the 7.2V AC at the power transformer is at 0V.
If I pull Fuse 6, then the AC goes to the expected 7V.
This does provide 6.6V to both the Right and Left Channels and my thinking that maybe this is the cause.

Any ideas what the issue might be? Am I on the right track with the 7.2V AC at zero volts?
 
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-maybe the new direction lamps have a short-circuit in the wiring or they exceed the 55 mA current limit.
-disconnect lamps for now to see if that changes anything
-remove the two muting transistors for now. deck will work fine without them. this is to see if you have a muting defect
-and collector of Q111 should always stay at 32 VDC in both play mode and in stop mode.

-in the 707 the transistors fail more often than the caps so you should have replaced them before the caps. Replace all 2SC1344 transistors.
 
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Thanks for your reply and did check the voltage plus removed the lights (LEDs)
It was working briefly but now the issue is back.
Not sure what happened or why.

Any recommendations for where to get quality transistors for the 707?
 
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did you remove the muting transistors like I indicated? Q113/114

And does collector of Q111 stay at 32V in both stop and play?

KSC1845 as sub for 2SC1344. Digikey or Mouser
 
Finally got back to working on the RT 707. I inadvertently shorted the direction light wire to the frame about 3 weeks ago and that killed any normal reel motion.
So, I had to get that resolved before going back to figure out monitor/play issue.
Ended up replacing the Control Assembly board (RWG 88) with one that I purchased off of EBAY since that seemed it would be the most likely culprit.
I don't have a schematic or circuit layout for this board, so troubleshooting is difficult.

Replaced the Control Assembly and now the reel motion and the tape monitor are both functional.
Paid $35 I for the used board and it was definitely worth the price.
RT 707 is working great.
 
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