"Jerry" wrote in message
ups.com...
On Sep 20, 9:38 am, "Arfa Daily" wrote:
Any of you good ol' boys across the pond, familiar with a Delco 15CFMT3
(or
might be a 25CFMT3 as it has two stickers on it, one red, one black, each
purporting to be the "service model number" ).

It's from a vintage Chevy, I believe, and a colleague asked me to have a
quick look, and that's all it's gonna be, as I really don't have the
time.
Initially, it had instability at about 50Hz, dependant on vol control
setting, It has a multi-section can-type cap in the back right corner,
and
this seems to be open circuit on one of its sections. I hung a 1000uF
temporarily across the bad section, and that knocked the instability
problem
on the head. I then tried the radio. There is plenty of livliness on AM,
as
in it picks up a few stations, and there are lots of shortwave-like
birdies,
but that is without a proper antenna connected, and in an electrically
pretty noisy environment (my shop!). On FM, it seems a bit insensitive,
but
again, that might be down to a poorly matched rod antenna that I am
hanging
on it. I don't know how well these old fellas performed in the first
place.
If they were anything like British ones from the same era, then it's not
very well as I remember.

So, on to the 8 track bit of it. Mechanically, it all works, including
track
selection, but audio-wise, there is just a horrendous mess on both
channels.
There may be audio at the back of it all, but nothing recognisable. It's
hard to describe the noise. Sort of a very random, but continuous,
distorted
'crackle'. Both channels exactly the same, and controlled by the volume
control. Given that the radio section / output stage works (sorta !) I am
guessing that this other problem must be in the 8 track head amp
somewhere.
I really am not going to go looking for it, as I really don't have the
time
or the inclination. I am not looking for general repair advice on it, as
I
repair hifi equipment for a living as most of you know, so am well
familiar
with fault finding. All I am looking for is if anyone remembers the model
and can say " Oh yes, That was a really common problem. It's C29 " or
whatever.

So, anyone got anything for me ? TIA

Arfa

Have you taken a close look at the 8-track cart you're using for an
audio source? The pressure pad that is used to push the tape against
the head is usually a cheap metal springy strip with an even cheaper
foam piece glued in the middle. Those old 8-track carts are notorious
for the foam disintegrating with age. If the tape doesn't make good
contact with the head, it's not gonna sound too good.

I discovered this a couple of years ago when I was trying to transfer
some 30 year old vinyl LPs and 8-tracks to CD - had to refurbish the
pressure pad on nearly every 8-track.

Here's a good online resource:
http://www.8trackheaven.com/

Jerry


Thanks both. I'll look into them tomorrow, but I don't think that it's going
to be either of them. The noise on the audio has got a distinctly
'electronic feel' about it. It's very hard to describe, but if it was on one
channel only, rather than both, you'd be looking for a rustling cap or a
noisy transistor - you know the sort of noise ?

Arfa