Pioneer CT-540 tape deck - no playback on right channel

I have already fixed the mechanical problem with this deck (idler tyre) now it plays, fast forwards and rewinds ok but there is no audio output on the right channel. Also nothing registers on the right channel bargraph display.

I have followed the general troubleshooting for tape decks in the FAQ; when I touch the terminal (white wire) from the left head output I hear a buzz but when I do the same with the corresponding terminal for the right channel I hear nothing. This leads me to believe that the problem is in the electronics rather than a defective tape head. Does anyone have any suggestions for common failures on this deck or perhaps a schematic diagram?

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Tim Phipps

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Tim Phipps
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It's common on all tape decks for the wires from the heads, to break, often inside the plastic sleeving. Give each a gentle tug to make sure that this isn't the case. The other very common thing for no playback on one channel, is the record / playback switch going bad, particularly if you don't record often. As a first move, locate the switch, and give it a vigourous scrub back and forth. If that produces a fix, squirt a little switch cleaner / lubricant in there, and repeat the scrubbing.

Arfa

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Arfa Daily

I checked for continuity on the leads from the head to the board and they were all ok.

The other very common thing for no playback on one channel,

I could not locate such a switch on this deck. For reference, it is logic controlled. The only internal switches on the transport are the one that stops the tape if the eject button is pressed and the one that detects if the 'record-protect' tab has been removed.

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Tim Phipps

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Tim Phipps

OK on that Tim. The record / playback switch is not usually located on the deck itself. It is normally a slide-type multipole switch, actuated by a rod or lever or stiff wire, from the deck. Whether or not the deck is directly controlled or servo controlled by logic, is not normally an issue, with regard to this mechanical scheme.

Some cassette machines, however, do employ full electronic switching, which is sometimes part of the record / playback subsystem IC. If this is the case with your machine, then you will probably not get much further without a set of schematics, and a 'scope. Have you tried to see if it records successfully on both channels ? If it does, that at least for the most part, proves out the heads and their wiring. It's pretty unlikely, but I'm assuming that you have not got a very badly clogged head ? Normally, you can still hear something on the affected channel, when playing back a previously known good tape, but just occasionally, you can get a case that's so bad, that you get nothing at all.

Arfa

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Arfa Daily

On Tue, 20 Jun 2006 21:52:06 GMT, Tim Phipps put finger to keyboard and composed:

You can eliminate the head as the source of your problem by interchanging the L & R wires in the connector. If the problem migrates to the other channel, then the head or cable is the culprit, otherwise there is a problem on the board.

- Franc Zabkar

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Franc Zabkar

Ok I had a good look over it again today and I'm pretty sure that this deck does not have a mechanical record/playback switch. The only switches on the board are those for selecting the tape type and Dolby NR. It would seem that it is done electronically although there are very few ICs on the board - mostly discrete components. As it happens I do have a scope that I acquired for free but I don't think I have much chance of obtaining schematics as it is a fairly old unit - appears to be made around 1983 going by the dates marked on the motors.

Just to check the head for sure I tried reversing the connector that goes to the board since it is wired symmetrically. Sure enough I got the same result - playback only on the left channel, although this time the signal being supplied from the right output of the head. This seems to confirm that the head is good and unfortunately it's an electronics fault. However, I did try a test recording and it records on the left channel only. I checked by playing back on a known good tape deck. If I turned up the volume on my hifi amp much higher than normal listening level with the balance control all the way to the right I was able to hear a faint signal. So it seems that it is a fault on the board which is affecting both playback and recording.

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Tim Phipps

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Tim Phipps

Thanks, I tried this by reversing the connector as it is wired symmetrically and still got playback only on the left channel so it seems the problem is on the board :(

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Tim Phipps

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Tim Phipps

It's quite unusual to have a fault which affects both record and playback of a channel, and is not the head or its wiring. About all that's left is the record / playback head switching, which may be done by a couple of FETs on each channel, although is much more commonly done inside an R/P process IC - even on a machine of that age, some kind of open circuit between the head connecor and wherever the switching takes place, or possibly, an open circuit cap in the path between the head and the switching. It is possible that the same amplifier stage is used on record and playback, and just " turned around " but this is not usually the way it's done.

One thing that you could try, is to put the unit on record, and then put the 'scope across each channel of the head in turn, and see if you can see the high frequency bias signal on both channels. This will at least prove that something can reach the head ok, although it doesn't tell us a lot, as the bias injection point could be literally just south of the heads connector. You might also try scoping at the record and playback level presets on the board, with a tape playing, or one recording, just to see what you get. Interesting problem that would no doubt be resolved in moments with a set of schematics.

Arfa

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Arfa Daily

The dolby chips would fail on these and occasionally an electrolytic capacitor would short. Chuck

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Chuck

On Fri, 23 Jun 2006 00:27:31 GMT, Tim Phipps put finger to keyboard and composed:

If there is any obvious symmetry between the left and right channels, I'd be playing a test tape (eg 1kHz sinusoid) and scoping the equivalent points in both halves of the circuit. Otherwise, if the signal disappears inside some R/P processor IC, I'd download its datasheet and hope that Pioneer's design follows the application circuit.

- Franc Zabkar

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Franc Zabkar

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