Pioneer SX-1280 Tuner Issue

satterdp

New Member
May I request some help with a SX-1280 tuner issue? I picked up a 1280 (basically working) for $250. Works well after a good Deoxit cleaning. The FM tuner signal strength is average. The tuning meter barely deflects to the left, mostly to the right. In addition, the meter is not centered (slightly to the right), even when powered off. I adjusted T6 on the tuner PCB per the manual, but could not adjust it far enough. From a powered off state, should I start by centering the tuning meter? I assume there is an adjustment screw below the face. If so, how can I remove the meter assy from the front plate? Any other overall ideas? Thanks!!
 
DO NOT TOUCH THE METER INNARDS. P E R I O D .!!!!!!!!!!! :yikes:

That screw is NOT a centering adjustment, it is PIVOT TENSION!!!

Centering is the incredibly tiny, sensitive, FRAGILE spiral spring.

If the meter is barely deflecting it is because the pivots have either been tightened by someone else, or the pivots have corroded, they form one of the two connections to convey current through the meter. There is probably a combination of mechanical resistance and electrical loss of contact varying with pointer position.

I have rehabilitated meters before by hooking them up to a sawtooth function generator that I adjusted to wider and wider swings over the period of a week or two. Just plain wore them back in to good conduction.

Otherwise, I suggest a salvaged meter.
 
Mark, great input - thanks! I think I will try a salvaged meter as you state, and go from there. Are you aware of how the meters are attached? I see no hardware, but I do see what appears to be clear "tape?" on the sides / top. Very much appreciate your input!!!
 
The tape holds the meter together (back portion with the scale and the front lens box). They are held in by brackets pushing on them IIRC (it's been a while for a 1280).
 
Thanks Mark. I removed the bracket, looks like they may be using a piece of double sided tape in front - attaching to the tuning plate. I will investigate further!! IIRC?
 
There is a circuit in existance, another later model, that used LED's as a replacement of a meter movement... now which one of the 100's is again :)
 
I was not aware of another later model that used LED's - very interesting. Fyi, I have an old Ferguson receiver (3426) from the mid 70's that utilizes two bulbs (bet nobody has heard of that receiver).
 
it isn't a LED, it's indicator segments in the fluroscan display. Sx-3700, sx-3800 etc
 
An update: Per Mark's recommendation, I "exercised" the meter for a couple of days, but no change. I procured a replacement meter, but prior to installing I "tapped" the old meter from the side a couple of times (after removing from the receiver), and the needle centered correctly. I ended up installing the new meter, and everything works correctly. Thanks to all for your assistance and ideas.
 
Darn, I overlooked one small but important detail, I got a mini drop of deoxit on the end of a 24 gauge wire, and transferred it carefully to the bottom pivot.

That exercise was ~ 3 hertz banging at it continuously for a week, so there would be ballistic overshoot and scrubbing when contact was lost. Leading edge of the sawtooth was the abrupt part of the waveform. When contact was regained at whatever part of the waveform, the needle would be PULLED to the correct position.

This is just for future reference, since your problem is solved.

Don't landfill the duff meter, send it to me? I'll see what can be done to rehabilitate and recycle it.
 
Apologies Mark - the meter is already history. I will be more careful next time. Thanks for all of your expert advice. AK is the best!!
 
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