Hi,

the front panel of the TM-455E UHF transciever I have here sometimes shuts off,
and the panel buttons stop working, but the transciever doesn't stop completely
and all microphone buttons work (PTT, vfo-mr...). I even think it'd be possible
to have a QSO.

The power button is on the front panel, so it's impossible to shut off or power
on the TX when the panel fails.

I suppose there's a problem with the front panel, because sometimes the LCD
displays an incomplete screen (I've seen it show the right frequency, but
without punctuation nor other symbols, or nothing at all, or all segments
half-on). Most of the time, it blanks completely.

Touching the PCB of the front panel has an influence on the behaviour (mainly
creating the problem, seldom making it work again), but I couldn't find any
specific component causing trouble. I've also checked for bad solder points, but
couldn't find any.

At first, I suspected the cable between the TX and the front panel was at fault,
but moving it doesn't change anything. I will have to check with another cable
anyway.

I'd be thankful for any hints or advice.

Matthias HB9EGM

In copier work, this occurs sometimes. It's usually a cracked trace on the
board, that when pressed or thermally expanded, it drops out. It can also
happen when the board moves a bit, and touches a little of the metal frame,
causing it to ground out. I hope that you find the problem without too much
grief.
73's
Tim
KK5H
"none" ""bram\"@(none)" wrote in message
...
Hi,

the front panel of the TM-455E UHF transciever I have here sometimes shuts
off,
and the panel buttons stop working, but the transciever doesn't stop
completely
and all microphone buttons work (PTT, vfo-mr...). I even think it'd be
possible
to have a QSO.

The power button is on the front panel, so it's impossible to shut off or
power
on the TX when the panel fails.

I suppose there's a problem with the front panel, because sometimes the
LCD
displays an incomplete screen (I've seen it show the right frequency, but
without punctuation nor other symbols, or nothing at all, or all segments
half-on). Most of the time, it blanks completely.

Touching the PCB of the front panel has an influence on the behaviour
(mainly
creating the problem, seldom making it work again), but I couldn't find
any
specific component causing trouble. I've also checked for bad solder
points, but
couldn't find any.

At first, I suspected the cable between the TX and the front panel was at
fault,
but moving it doesn't change anything. I will have to check with another
cable
anyway.

I'd be thankful for any hints or advice.

Matthias HB9EGM

robo tech wrote:
In copier work, this occurs sometimes. It's usually a cracked trace on the
board, that when pressed or thermally expanded, it drops out. It can also
happen when the board moves a bit, and touches a little of the metal frame,
causing it to ground out. I hope that you find the problem without too much
grief.
73's
Tim
KK5H

Hi Tim,

thanks for the info, that seems quite possible, but it's difficult to find
because it's difficult to see.

Matthias HB9EGM

none wrote:
(Snip)
couldn't find any.

At first, I suspected the cable between the TX and the front panel was
at fault, but moving it doesn't change anything. I will have to check with another
cable anyway.

I'd be thankful for any hints or advice.

Matthias HB9EGM


I am sure you will try the obvious to look with your eyes for broken or
pinched parts, tighten grounds, re-seat plugs and clean off any
oxidization.

From time to time I have had to troubleshoot equipment with partially
intermittent components or circuits. Freeze spray is sometimes
recommended, however I find freeze spray is not easily localized and
instead causes moisture to short out other sensitive circuits leading to
mis-diagnosis.

What you might first try, is to use artist's paint brushes of various
stiffness to probe the various components until the intermittent one is
found.

Secondly, if you do isolate an affected circuit schematically, but not
physically, you can use a trick I have used which is to use a small AC
coupled audio amplifier across the circuit to ground (biased either by
operating voltage or Ohmmeter) and listen for a micro-phonic affect as
you move the affected parts.

--
Joe Leikhim K4SAT
"The RFI-EMI-GUY"©

"Treason doth never prosper: what's the reason?
For if it prosper, none dare call it treason."

"Follow The Money" ;-P