The HT sub started to act crazy, it would work ok for a couple of hours, but then the bass would eventually disappear.
I pulled the amp out and noticed a pair of caps were swollen, replaced them easily with the same value and it started working again.
That was encouraging but soon noticed the transformer was getting hot, very hot and this plate amp wasn't even back in the enclosure; which is a sealed plastic box inside the speaker box. I left it out on purpose just in case of something like this.
Not a lot of components on the plate amp, and they all look in good shape.
Since the plate amp is not in the box, I didn't reconnect the LEDs - Con3a1
Would hate throwing it away, any hope with this?
Thanks for looking!
I pulled the amp out and noticed a pair of caps were swollen, replaced them easily with the same value and it started working again.
That was encouraging but soon noticed the transformer was getting hot, very hot and this plate amp wasn't even back in the enclosure; which is a sealed plastic box inside the speaker box. I left it out on purpose just in case of something like this.
Not a lot of components on the plate amp, and they all look in good shape.
Since the plate amp is not in the box, I didn't reconnect the LEDs - Con3a1
Would hate throwing it away, any hope with this?
Thanks for looking!
Attachments
Disconnect the two red wires from the transformer to the circuit board. If the transformer gets hot, it is the transformer (broken). If it stays cool, reconnect and check if the heat sinks heats up. Then it is one or more of the semi's there which is broken.
The transformer might have a self resetting thermal cutout, which caused it to work for a few hours before quitting. Sounds like it may have been doing this for a while. It could have a short between adjacent turns - unhooking it and seeing how hot it gets is the test for that. If the short was on the primary side you could end up with too much voltage, which may have been what killed the caps. If the short is on the secondary side, voltage will be a little low instead. Either will result in lots of heat. If it runs cold with no load its fine.
It is also possible there is something wrong in the amp. There are things that can go wrong where it still “works” but draws too much current. If that happens, the transformer and heat sink will run hot. It could also take out the caps due to higher than expected ripple current (which will wear them out quickly). If the amp is drawing excessive current but still “working” the drive waveforms to the output FETs are probably incorrect (a slow fall time would do this). Unfortunately, hard to check without real test equipment.
It is also possible there is something wrong in the amp. There are things that can go wrong where it still “works” but draws too much current. If that happens, the transformer and heat sink will run hot. It could also take out the caps due to higher than expected ripple current (which will wear them out quickly). If the amp is drawing excessive current but still “working” the drive waveforms to the output FETs are probably incorrect (a slow fall time would do this). Unfortunately, hard to check without real test equipment.
Ok just got back and plugged it in with red wires removed, faint-hum but doesn't seem like a high current draw, but I'll let it run for a few hours.
I'm sure this has been going on for a while, progressively deteriorating / getting warmer; couldn't believe the smallish, no-vent enclosure that the amp slides into when disassembling.
I'm sure this has been going on for a while, progressively deteriorating / getting warmer; couldn't believe the smallish, no-vent enclosure that the amp slides into when disassembling.
90 degrees F may be normal for a cheap Chinese transformer. 90C would be what happens if there were an internal short. Pull your hand back sort of “hot”, not just the place your cat would curl up to on a cold day “hot”.
And an otherwise “normal” power trafo given 125 volts that would run at 90F sitting out in open air on the table might very well climb to 190 inside a one cubic foot sealed box for three or four hours.
If it climbs to more than 125F (or about 50C) sitting out in the open (leave it all day) I’d be worried that something is physically wrong with the transformer. It could just be marginal/poor design with a bit too high a line voltage. Which is par for the course with retail consumer electronics. If the caps were marginal, that’s why they were worn out. The heat from the transformer probably contributed.
If it climbs to more than 125F (or about 50C) sitting out in the open (leave it all day) I’d be worried that something is physically wrong with the transformer. It could just be marginal/poor design with a bit too high a line voltage. Which is par for the course with retail consumer electronics. If the caps were marginal, that’s why they were worn out. The heat from the transformer probably contributed.
When a transformer of any kind has a shorted turn, it not only will run too hot, it will no longuer support load nor will give proper voltages at the output. Also it must smell bad. And there is no going back.
If line is high, 125V of a normal of 110, it means about 11% more voltage. Perhaps it is entering into saturation. There are ways to stop it.
If line is high, 125V of a normal of 110, it means about 11% more voltage. Perhaps it is entering into saturation. There are ways to stop it.
11% more voltage can be 200% more magnetizing current if it was designed up against the edge of saturation. It will also make a noticeable mechanical hummmmmmmmm.
Bean counter approved designs have a tendency to do this. It’s also why I never buy powered speakers. Anything without a $4000 price tag usually has compromises like this.
Bean counter approved designs have a tendency to do this. It’s also why I never buy powered speakers. Anything without a $4000 price tag usually has compromises like this.
Higher costs don't always mean perfection, great design, or elimination of potential issues.
Heat continues to rise, 105degrees and not in any enclosure.
I unplugged it in case there is a replacement and the voltages are needed.
I unplugged it in case there is a replacement and the voltages are needed.
I’m assuming F, not C. If it were 105C it would be plain as the nose on your face that it’s bad. It would be smelling up a storm.
Cheap Radio Shack transformers used to run 120F, and do it for years. Doesn‘t indicate good design practice, but doesn’t mean instant death.
To a point, yes.
But just as factual, cheap products sometimes outlast expensive ones.
So it goes both ways.
I purchased a $27 Cyberhome DVD player in the mid 1990's. (Walmart Christmas "doorbuster sale")
Gave it as a Christmas gift to a friend.
The thing never had a problem, still works!
I've had several of them in the shop, all in perfect operating condition - donations from customers who bought expensive ones, and those expensive ones showed up later for repairs!
I even took a cheap Cyberhome home to install in my home-made jukebox as a CD/MP3 player - no issues.
Matter of fact..... I've had MORE expensive products come in for repairs over the decades than budget stuff.
105°F, The longer it is on - the temp continues to rise. However, I checked the amperage-draw at the power cord, very, very, low.
Found a Data Sheet online:
https://pdf.datasheet.live/cef1dd54d24000c56819a6969ec36888.pdf
The only symptom is the heat buildup, no pops, etc. might as well keep using it with a mini cooling fan.
Found a Data Sheet online:
https://pdf.datasheet.live/cef1dd54d24000c56819a6969ec36888.pdf
The only symptom is the heat buildup, no pops, etc. might as well keep using it with a mini cooling fan.