Roland RE-301

[rafe]

Is there anyone that can help me troubleshoot this ...I've had it over 5 years and used it a little when i got it ...it functioned well...it most likely sat a long time before that ....Today I was using it for the first time in 5 years and it was ok ...scratchy pots but otherwise good ....when the echo failed every thing else works sound on sound ,chorus, reverb.....the pot that controls the volume of the echo is making lots of noise that goes mostly away with turning it down but there is no echo.....but again sound on sound will record....it has 3-25/1000 caps in the power supply but I don't know if they would cause this....I am thinking It is beyond my scope...a lot of the testing is wave forms...any way anyone who has experience with these please chime in....
  

[six_eight]

I've never worked on an RE-301, but if you had the service manual that shows the schematic and layout, that would be a tremendous help at taking a stab.  I did a quick search and couldn't find it.  However, if you call Roland USA, they will usually send stuff from their archives for $3. 

Does the scratchy sound happen only if you're actually turning the pot, or is there a constant background noise that you can control the volume of with the echo level knob?  If everything but the echo is functioning, that's a good sign.  At least you know where in the circuit to look.    If you are hearing a volume change in the scratchy noise when you turn the echo level knob and you can still hear dry signal, that means that the output buffer of the delay portion of the circuit is still working.  We can assume the input buffer is still working as well because if it weren't you wouldn't hear any dry signal.  So I would guess that that rules out everything but the most obvious culprit - the actual tape recorder/playback. 

Look inside and make sure the tape looks ok and the motors are running and the tape is spinning.  If not, I would assume you need to replace the motor.  If it is moving, it could be several things.  I'd probably start with replacing the tape it you want to start throwing hail marys.  The tape or the motor are usually the first things to go.

If other parts of the unit are functioning fine, I would assume the power supply is fine.  However, if the tape delay portion of the circuit has its own regulated power supply, that would be a place to look as well.

[rafe]

Hi six-eight, The tape is moving fine and the motor that moves it responds to the speed increase decrease. The machine has a sound on sound feature which will record what you play and then replay it one time so you can play along with it, not slap back it records the whole loop once, because that function works I believe the recording function is fine.although it appears that it is a seperate head ..I have the manual
Does the scratchy sound happen only if you're actually turning the pot, or is there a constant background noise that you can control the volume of with the echo level knob?

It is constant and I control the volume level with the pot

http://archive.org/stream/synthmanual-roland-re-301-service-notes/rolandre-301servicenotes#page/n13/mode/2up

[six_eight]

That's excellent news...well...in terms of locating the problem.  Actually getting the parts to repair it might be another story. 

I wasn't sure what the SOS feature was, but now looking at the schematic, it makes more sense.  P4 is the SOS head.  P1 - 3 are the echo playback heads.  Take a look at page 13 of the reader (7-1 overall circuit diagram).  You can see VR14(p4), 15(p1), 16(p2), 17(p3).  These are the internal trimmers that adjust the volume of each playback head.  The signal from p4 goes straight to the output jacks (after going through another buffer and mixing with the dry,chorus, and reverb signals.

The signal from p1, 2, and 3 mix together at IC13a.  Before the output from the buffer at IC13a mixes back in with the p4, dry, chorus, and reverb signals, it also goes to two pots: VR6(echo intensity) and VR7(echo).  I've always hated Rolands names for delay parameters.  Intesity is "repeats", and echo is "delay level".  I would think most people would assume that "intensity" would be the level, and "echo" would be the repeats. Anyhow...

VR6 is the feedback loop which sends signal back to the recording head.  VR7 is just a passive volume knob for the echo signal.  Lug 3 of both the pots are connected at the same place.  The IC13a buffer is putting out signal if you are getting a constant crackle sound.  The problem is that IC13a isn't getting any signal from P1, P2, or P3.  This doesn't necessarily mean that the problem is with any of those playback heads.  Hopefully, that isn't the problem.

So the good news is, we've narrowed down the search to a very specific part of an otherwise overwhelming circuit.  If you have an oscilloscope or an audio probe, you can trace out the signal from the 3 playback heads(page12) to IC13a(page13).  Hopefully, you're getting some sort of echo in there somewhere, and more importantly, you can find where it's dying.  Unfortunately, there's a little bit of the schematic that got cut off between the playback heads and Q23 - 25.  These are JFETs.  You should be able to hear signal with an audio probe at the gate of each of these.  If you can't detect any signal at the gates of those 3 JFETs, then it probably means the playback heads aren't working.  It's odd that all 3 would go tits up at the same time though.  Maybe they all share a common ground wire that's come loose.

[rafe]

Six_eight...I do appreciate the feedback ...I will see if I can chase down the problem, like you pointed out, you have concentrated(narrowed down) the area of concern...I will go over that, most likely tomorrow, and see what I find out, I'll post back the findings Thanks and regards Rafe