"Tim Phipps" wrote in message
...
Arfa Daily wrote:


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

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.

--
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