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Pioneer RT-909 FWD/REV head mute switch?

OscarEmmy

OscarEmmy

VHFSE Originator/Blogger
Today I bought a mint-looking RT-909 from a yard sale; it works beautifully in reverse, but in forward play I can hear all four tracks (that is, both the forward track and the reverse track, which is of course playing backward!).

Does the RT 909 deck have any kind of head mute switch that should be cutting in when I change the direction of play? I imagine it does, otherwise I'd also hear this problem when playing the tape in reverse play --- which I don't - there's no obvious crosstalk there at all.

Is there a kind of head mute switch that maybe gets stuck in some way with disuse? If so, does anyone on AK know a fix for this?
 
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If i remember right, there is some sort of relay or switching transistors that are supposed to do this. Got the service manual yet? It will show you the schematics.
 
Have you tried more than one tape? Is the tape you played "home made?" If so, see if you can dig up a pre-recorded 4-track tape to confirm the fault exists. Want to make sure the tape wasn't recorded on a multi-track machine!
 
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BANDWIDTH said:
Have you tried more than one tape? Is the tape you played "home made?" If so, see if you can dig up a pre-recorded 4-track tape to confirm the fault exists. Want to make sure the tape wasn't recorded on a multi-track machine!
Click to expand...

:lurk:
 
BANDWIDTH said:
Have you tried more than one tape? Is the tape you played "home made?" If so, see if you can dig up a pre-recorded 4-track tape to confirm the fault exists. Want to make sure the tape wasn't recorded on a multi-track machine!
Click to expand...

I have other 4-track machines, and tapes that play normally on those play with this issue only on the RT-909, and then only when playing forward - they play perfectly in reverse mode, so it can't be the tapes.

I don't have manual yet, but I will get one and try to see how the playback/record circuits are configured. There MUST be a mute circuit that is not cutting in. The same problem occurs when recording in forward mode!
 
Mrv8q said:
HiFi engine has the 909 operating instructions....
Click to expand...

Thanks. I have those, as well as the service manuals and schematic, all from that same website.

The service manual describes the head muting circuit on p.19 http://www.hifiengine.com/library/pioneer/rt-909.shtml but I'm not really any wiser about how to check for a fault. Perhaps someone familiar with that process can advise me? I can't afford to send the deck out for a major service.
 
This circuit generates the voltages that control the switching FETs at the outputs of the play amps.

You should have +15 volts at the middle arrow at the junction of 2 transistors.

For the other 4 arrows, tell me the DC voltages in play and reverse play. My guess is that one is stuck at a certain voltage (and not switching).
 

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