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AM21 low signal strength

1K views 17 replies 7 participants last post by  slice1900 
#1 ·
My AM21 has been working more and more poorly over the last few years to the point where it mostly pixelates. Using OTA and the TV tuner works fine. So I felt the issue must be in the AM21. I am no electronics expert but I now what parts are, how they should look and can easily visually see a burnt resistor, cooked fuse or transformer, bulging and/or leaking capacitor.
So I figured I'd take a look inside and see if there was anything obvious. To open the AM21 and remove the board, you need a Torx 10 security bit (drilled for the security pin). Both the cover and the board use them. Get the bit.
As soon as I opened it, I could see four bad capacitors all around the RF tuner. 470UF 10V. All split on top, bulging and oozing. I've ordered replacements @ $2 each delivered. It would be a lot cheaper if I had a local store but I have to do online and shipping. I am not positive this will fix my AM21 but it will not make it worse! Bad caps, circled in red.
Passive circuit component Black Circuit component Hardware programmer Audio equipment
 
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#7 · (Edited)
A, I got you. Really depends on where you live. No electronics stores near me, so on line. I've seen quality caps go for under $0.50 each and crappy ones selling for $5.00 each! I selected ones from a name brand manufacturer and rated for high frequency (like a RF section of a radio/TV and not ones designed for low frequency as used in a power supply.
I paid $8.00 for six, delivered via Amazon. 470UF !0V low ESR
I'm a beginning HAM and have been reading all the books. I have a slight electronics background. Not enough to design my own circuits, but enough to read a schematic, and do basic troubleshooting. As long as my old eyes do not fail me....
 
#9 ·
Caps arrived this morning. Removing the old ones from the board were tough. Through hole solder and it seemed to be high temp solder as well. One at a time, watching polarity. Took old me close to an hour, just to R&R four caps.Hooked it up, only tuner 2 came to 100% (up from 25%) Tuner 1 was still 25%. Crap. poor workmanship. Apart it came for a resoldering. Resoldered all, ensure flow through the holes. Damn bad eyesight! Reconnected, both tuners to 100% Success!
 
#13 ·
You have inspired me to attempt the same repair story. I am waiting for a star torx socket I just bought on ebay to open the box. The box is owned by me so no concern about violating TOS. Until the new LCC's are available I am going to try to repair one of my AM-21s.
 
#12 ·
Too many SMD parts that I'd spend hours listing. nothing in it for me. However, if someone wanted to give me a few hundred to meticulously itemize all the parts, orientation, photograph the traces, that would be a different story.
 
#16 ·
The device went back to 25%. While the caps I replaced were bad, something else is bad/wrong as well. Perhaps a SMD part is not making good contact and when I was 'man-handling' it, I made temporary contact and subsequent hot/cold cycles 'broke it' again. I had a friend who is a electronics tech look at it and he said the RF section was outputting a strong signal but that once it got to the tuner processor, without a service manual detailing the digital signals and testing, he was unable to check further.
 
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#18 ·
They are still only about 1/3 done fixing the OTA channel lists in various markets. I think it is safe to say they plan to have that done before the LCC is released. So most likely it will be a few more months, at least.
 
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