The lack of high band channels on that set is almost always bad
electrolytic capacitors, especially on the 33v line.

The next and previous channel feature is simply probably worn out
buttons on the remote control. Does the channel up/down work on the
tv or have those been liquid damaged from someone cleaning the glass?

The channel up/down requires that the tv be autoprogrammed properly,
if the electrolytic capacitors are weak the aft will not lock in fast
enough and no channels will be stored in memory.

From years of experience, one feature of a system control does not
simply stop working. In 99.99% of all cases either the system control
is working, or it is not. This is not including sets that store
feature levels in the eeprom in which case the eeprom could have bad
data making some features go away.

David

wrote in message ...
Channel up/down & higher channels inoperative

A double whammy, but are they related?

Problem 1: Some months ago, following a nearby lightning strike which
took out the electricity, and undoubtedly induced some "extra
potential", the channel up/down and retune (prev chan) functions
became inoperative. Channels can be selected and the current channel
recalled via the remote control.

My chief suspect is the main board circuitry associated with the
TMP47C634N2454 microprocessor, ICA01 (p/n 23318860). Since other chip
functions seem to work, I question if the IC itself is bad. Another
possibility might be ICA02, the M6M80011L memory chip (pn 23318861),
which I am guessing holds the preset and recall functions which may be
necessary for next and previous channels.

Given the age of the set, the tuner inconvenience was bearable, since
picture and audio performance are as good as they have ever been. A
couple of years back a general recapping in conjunction with the
well-known fused R327 resistor problem restored the unit to like new
performance.

Problem 2. Yesterday, within a period of 5 minutes, both audio and
video on the upper channels deteriorated to the point of complete loss
on channels 49 and higher. Following a lengthy cool down period with
power off, the higher channels are perfect and then in 3-4 minutes
suddenly drop video and audio with a loud schrunch. The lower channels
2-48 work perfectly.

My first suspect is the EL811Lx1 VHF/UHF tuner module, (pn
23121639)but I question why the lower channels continue to function so
well. I am reluctant to replace the tuner, pretty much a
cross-the-Rubicon action, as well as time consuming and expensive,
without a better understanding of the problem. I am wondering if
someone has experienced this before, or at least may have some other
leads to investigate.

A scan of Toshiba tuner problems seem to suggest failed solder joints,
but I wonder why that would affect only channels above 48. I am less
inclined to suspect the SIF/PIF board, however, I am wondering if the
microprocessor input to the tuner may be at fault, linking both
difficulties.

Any thoughts on the matter would be much appreciated.

Dave Allen
Falls Church, VA
daveatallencitycom