(Repost) Zenith TV model B25A24Z no sound .Really need help!!!!

[Lenny]

I'm posting this again in the hopes that perhaps someone who didn't
see it last time may be able to help me now. Thanks.

From: Lenny ([email protected])
Subject: Zenith TV model B25A24Z no sound


View this article only
Newsgroups: sci.electronics.repair
Date: 2004-02-07 05:35:11 PST


This set has no audio from the speakers or the variable output jack in
the back. I tried full volume and still heard nothing. I checked the
menu to be certain stereo, SAP., surround, mute, etc were all where
they should be. The thing I did notice was a slight barely audible
"thump" noticeable when switching the speakers on through the menu. So
although I didn't fully investigate it I suspect that the output is
good. I didn't try any signal injection yet but without a schematic
this is a bit difficult. Does anyone have any information on this
model having these symptoms or could you perhaps point me in the right
direction? Thanks in advance for any assistance. Lenny Stein, Barlen
Electronics

 

[JURB6006]

A really important piece of information would be whether the set reponds to
audio through the AV jack. At least then you narrow it down to either the MTS
decoder or the switching ckt.

You can walk around sets without a schematic, so armed with this piece of
information it's not that hard to find the MTS and switching ICs. After that
someone in here is bound to know a cross from a 221-XXX IC to a jantx
(standard) part number. That begets the pinout, in fact then the ECG book might
provide at least a pinout. If it's in ECG, you can also back cross it to a
generic.

I've done this several times, I just remember the ECG number and start on the
right side columns of the cross, starting in AN, then BA then LA, TDA TA uPc
etc. This trick works on NAPs too.

As far as I know the ECG type of software specifically doesn't allow for
backcrossing for obvious reasons. Gotta do it in the book, and it'll be a shame
when they go the route of the TV manufacturers and make you use some screwed up
proprietary software.

I've seen some Zeniths with the solder connectioins to the rear jack panel so
bad that like NONE of them were making connection for a long time. Makes me
wonder if the set was oned by deaf people ! It obviously didn't happen
overnight. I don't think this is your problem though if you hear anything at
all. Due to the physical design of the board on the ones I'm talking about you
can't effectively move much by smacking it around.

Other problem is I've worked on few Zeniths and the model number doesn't help
me to know which Zenith it is. On Zeniths I always try to post the 9-XXX number
of the modules it uses, and indeed if you're in Repairworld many many symcures
are listed to the module number. Actually it's more logical for obvious
reasons.

If you post the module numbers I can find one in the scrap heap at work to get
an idea what you're dealing with.

Another indication of where the trouble is would be if the set indicates that
it is recieving a stereo signal. There are ways. If it doesn't have a stereo
light other than the OSD, does it say stereo ? A VCR ch4 output should give a
different indication when you change channels or sometime.

For the AV input working or not, IIRC most Zeniths don't mute audio in the
absence of video. The source can be anything you could plug into the aux input
on an audio amp. Lacking something handy I've acually used a jeweler's
screwdriver with just my hand touching it so it would give me the familiar hum,
like you get when the ground of an RCA plug isn't making contact.

Anyway, a little more info and we can go from there.

JURB