I've got an Emerson ( ~ Sangean) ATS803 that has started to mistune.

Example:

Basic commercial FM band tune in 99.1MHz and get intermittent
shift in recieved signal as high as 99.9, with no alteration
in displayed frequency (reads 99.1).

This gradually worsens (by frequency pull) until the 99.9MHz
signal is continuous. To get 99.1MHz signal out then I have to
tune displayed frequency to ~ 98.4MHz. This is just a notable
example - smaller shifts have been seen (AIR). I've had to
retune the display downwards in increments to keep the 99.1MHz
reception.

It is physically dependent on something. With the case open,
pressure on front display can induce it, though all ribbon
cables have a fibre insulator installed to prevent pentration
of sharp component leads.

With RF board lifted, there seems no predictable or repeated
movement of anything simple that can induce it, but movements
of the entire rf board will: This can occur with RF board close
or distant. No assembly pressure on cables is required.

Tapping/wiggling cables and connectors doesn't aggravate or
repair it. Tapping/rotating the digital tuning assembly doesn't
affect the intermitency.

Finger placement/force on RF board doesn't change anything.

It's sitting on the bench open and behaving, but I can induce
problem with mech RF board movement or by reassembly at any time.

Ack.

RL

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It's sitting on the bench open and behaving, but I can induce
problem with mech RF board movement or by reassembly at any time.

And that is your best clue!

I suspect that there is an intermittent in one (or more) component on the RF board - a lifted leg, cracked leg, cold solder or similar that goes intermittent with heat, vibration, or just plain cussedness. Not knowing (but suspecting) this board is
mostly SMT devices, if you have a thin bamboo skewer, you might try tapping on the individual components to try and get to a specific culprit.

Good luck with it!

Peter Wieck
Melrose Park, PA

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On Thu, 16 Feb 2023 10:15:31 -0800 (PST), "Peter W."
<[email protected]> wrote:

It's sitting on the bench open and behaving, but I can induce
problem with mech RF board movement or by reassembly at any time.

And that is your best clue!

I suspect that there is an intermittent in one (or more) component on the RF board - a lifted leg, cracked leg, cold solder or similar that goes intermittent with heat, vibration, or just plain cussedness. Not knowing (but suspecting) this board is

mostly SMT devices, if you have a thin bamboo skewer, you might try tapping on the individual components to try and get to a specific culprit.

Good luck with it!

Peter Wieck
Melrose Park, PA

RF board on the ATS is through hole, I'm not sure how much
of the digital board is SMD

Think pre-1987.

The actual reception is fine.

I replaced the clock batteries, seeing as how it was open anyways
and reassembled the thing, under operating power, when and while
it continued to behave normally.

Issue hasn't recurred, but is expected it to show up again.
Squeezing the body in the display area no longer produces
the symptoms, though.

Will check the schematic to speculate, in the meantime.

RL

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Through-hole makes a wonky lead (or trace) even more likely. Anything from a cracked lead, cold solder to no solder at all. Then, check all the traces as sometimes thermal shocks will crack them.

Peter Wieck
Melrose Park, PA

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