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What electronics have YOU fixed lately?

TM86

Supporting Member
Jul 6, 2014
954
1,307
153
Payson, AZ
Sort of electronic. Fixed the darkness in my garage with some LED strip lights made to look like fluorescent fixtures. Spent a good part of the day putting in boxes, running wire, and getting them mounted. Bright as day in there now.
 

TM86

Supporting Member
Jul 6, 2014
954
1,307
153
Payson, AZ
Tram D80. Converted it from a smoke generator to a radio. Someone had apparently hooked the power up backwards, frying the reverse polarity diode. Next guy in the chain plugs it in to test it, and cooks the two chokes on the power lines. Guess the diode failed shorted. Replaced the chokes and the diode, it's happy again. Recapped it and removed the Sony bond while I was in there.
 
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TM86

Supporting Member
Jul 6, 2014
954
1,307
153
Payson, AZ
Sears "934.38260700". PLL wasn't looping, although the VCO was oscillating.

Found that the mixer for the loop downmix had two inputs, no output. Took the easy way out and swapped the transistor, no go.

Checked voltages, and the emitter was at 2.3V while the base was at 1.4V. That's not how an NPN works.

Much probing of stuff later and noticed that what was supposed to be the "ground" for the downmix oscillator signal (it's in a little can above the main board) had 2.6V on it.

Hmm... what happens when you swap these two wires? The PLL immediately got lock and it at least has receive now.

So, if you're ever working on one of these, the white wire goes to P33. The white wire with the black stripe goes to P34. They're marked "OUT" and "GND" , respectively, on the little board in the can. Just in case somebody changed the wires out with "prettier" colored ones.
 

TM86

Supporting Member
Jul 6, 2014
954
1,307
153
Payson, AZ
TRS Challenger 460. Bought as "guaranteed DOA." Was poking for places to put an oscope probe when it started working. Reflowed stuff around where I pressed, didn't quite fix it.

Went in with the magnifying glass and found that little circle in a solder joint that tells you it's broken. It was the anode of D1, the varactor diode for the VCO.

Which explains pretty much everything.

Reflowed that joint and now I can't make it stop working.
 

sunbulls

Sr. Member
Apr 25, 2017
891
1,601
153
73
I had to replace the power supply caps for the fourth time in my old ViewSonic monitor today. Keep in mind I only use so called quality caps such as Nichicon and Panasonic. In some cases I increased the working voltage thinking that may help, but that didn’t seem to increase longevity either. At best the caps only last for about two years. I’ve been using a wide screen Dell as a backup, but the glossy screen on that one has too much glare for my liking. I would have scraped this ViewSonic years ago, except for the almost glare free screen, high contrast, and its pixel perfect (important for graphic work). While I had it apart I also replaced the ON/OFF tactile push button that was intermittent. Fortunately there was enough room on the front panel to mount an old school SPST momentary button. Tactile “pop” buttons are a pain to replace and they’re not made to last.
 

nomadradio

Analog Retentive
Apr 3, 2005
5,213
7,407
573
Louisville, KY
www.nomadradio.com
Circuits in a CRT monitor that filter power supply ripple at 20 or 40 kHz call for electrolytic caps made for that service. Used to just use the original part number from the failed part, rather than trying to plow through data sheets for the right cap.

Could it be the caps you're using have too much self-inductance for the frequency at which they operate?

Just a thought. Did repair CRTs long enough to watch for quirky type filter caps. Won't get me to mess with one now.

73
 

sunbulls

Sr. Member
Apr 25, 2017
891
1,601
153
73
Circuits in a CRT monitor that filter power supply ripple at 20 or 40 kHz call for electrolytic caps made for that service. Used to just use the original part number from the failed part, rather than trying to plow through data sheets for the right cap.

Could it be the caps you're using have too much self-inductance for the frequency at which they operate?

Just a thought. Did repair CRTs long enough to watch for quirky type filter caps. Won't get me to mess with one now.

73
These caps probably have trouble handling the higher frequencies, but even the originals didn’t last long (no doubt some design flaw). I’m always running the maximum refresh rate that this monitor recommended. I believe a lower rate would put less stress on the power supply, but I found the lower rates were too hard on my eyes. Anyway, I’m satisfied with having several years runtime on a new set of caps, plus I mastered the teardown sequence. It took me less than an hour to be up and running again at a cost of around $10. The main expense is the 100uf 400v cap.
 
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