On Sep 20, 8:47 pm, "Arfa Daily" wrote:
"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- Hide quoted text -
- Show quoted text -
I know you're not looking for generic advice but I had a Delco Am/FM/
cassete radio in my 1983 Buick years ago. It had small micro switches
that engaged when you loaded the tape. They used to have to be sprayed
regularly. And that would do the trick for a while. It was a bitch of
a job getting at them without pulling the radio too. Finally I broke
down and disassembled them and resurfaced the contacts inside and that
was the end of the problem. That statically crackling you are
describing sounds very reminiscent of my old car. Lenny Stein, Barlen
Electronics