Rod, at 08:20 on Mar 25 1996, you wrote to Bill Grimsley...

BG> So that eliminates almost everything except the tuner's SIF.

RS> Yeah, thats what I meant. It does appear that whats
RS> involved in getting the audio off the IF has carked it.

BG> No, that just never happens.  It's one of those things
BG> which are so reliable, that they more or less work forever.
BG> I've lost count of the number of VCRs I've done over the
BG> years, but not one of them has ever had that problem.

RS> Well, it may well be extremely rare, I find it
RS> hard to believe that its utterly impossible tho.

Almost nothing is impossible, but SIF failure in VCRs and CTVs comes close.
 Ask your local techos and they'll tell you much the same thing anyway.

RS> Since the audio works fine when playing a tape recorded on the other
RS> VCR, clearly the audio chain out from the audio head to the connectors
RS> on the back must be fine. The problem must be with extracting the audio
RS> from the IF to either put it out the connectors with the VCR is used as
RS> a tuner, or onto the tape when you record a tape.

PB uses entirely different circuitry from E-E, and this is switched with a
PB logic high from the uPC.  Same with E-E.

BG> Yeah, and the more I think about it, the more I can hear an a alarm
BG> bell ringing somewhere.  I may have had this problem before with an
BG> NEC, and I'm sure it was not that the audio was faulty, but being
BG> muted via an external source.  It's nothing simple, like your dog has
BG> stuck it in simulcast mode by accident, or similar?  That would give
BG> much the same effect.

RS> True, good point come to think of it. It certainly has that
RS> mode. It could be just a switch failure or something there.

Or a crook AND or NAND gate switch in the logic circuitry, either muting
the E-E audio, or perhaps not switching it on.  Without the manual though,
it's impossible to say for sure.

RS> You didnt answer the question on how the audio is extracted from the IF. 

Didn't seem too relevant, given the symptoms.

RS> My recollection is that there is an xtal which determines
RS> the offset between the sound and vision carriers and so presumably
RS> if its not oscillating anymore you would lose the audio.

Most later CTVs (and nearly all VCRs) use either 5.5Mhz ceramic resonators
(which do occasionally fail, but it's still extremely rare), or a
quadrature detector IC with a tuned circuit (either R/C or ceramic
resonator) to determine the precise 5.5MHz SIF.  These passive bits hardly
ever fail either.

RS> The other possibility presumably is that the IC which generates the
RS> audio from the IF has just died on the bit where the audio comes out,
RS> presumably there is some form of amp driving that pin on the IC etc.

The IC can fail occasionally, but I've never had this happen on anything
other than the very early shitbox Goldstar VCRs.

RS> I used the opportunity of Telstras 9c/min with 15% off that with the
RS> Smart Saver to ring around a few obvious Sydney discounters yesterday
RS> and was a bit surprised to discover that the prices of an LP VCR,
RS> not a HiFi LP, havent changed in the 5 years since I bought the last
RS> VCR, in the high $400s. 

The prices may not have changed, but the quality sure has.  And it's not
been in the direction you or I would have preferred, either.  :(

RS> Currently the NEC VN64 sound like it might be the way to go, mainly coz the 
RS> VCR which still works is an NEC LP which might be handy with remotes etc

Yeah, the IR frequencies should remain the same between models.

RS> and should hopefully minimise any quirks when playing an LP tape recorded 
RS> in one on the other.

That's irrelevant, as all LP machines should be aligned identically, so
that tapes from any brand will be interchangeable with other machines.  If
they're not, the thing hasn't been aligned properly, simple as that. 
Having said that, it's quite rare to find any 2 LP VCRs which have been
aligned so that tapes from one can be played in the other without the use
of the tracking control.

RS> There was also a Sharp at $439 in an SMH ad.

If it's HiFi LP, that's the one I'd personally be buying.

Regards, Bill

--- Msgedsq/2 3.20