Electronics > Repair
OPA150 Stereo AMP issues, only turns on when I physically heat it up w/ a dryer!
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N19htmare:
Amp is a Dayton Audio APA150 https://www.parts-express.com/dayton-audio-apa150-150w-power-amplifier--300-812.

I've had it for about 6 years. It came with a 5 year warranty, believe or not, a MONTH after warranty expires, this started to happen. Customer Service at the time told me tough luck, I can buy another. since then I've just been dealing with it but it's getting worse. I'll list the problems and what fixes it in a list, I feel it is easier to read.

THE AMP:

* Amp is made of three boards, the main power board and left/right channel board, each of the channel boards has a RELAY, this relay is what I hear "CLICKING" when the amp either goes on or off. I think this relay is what gives this amp the Auto Turn-On feature.
* The toroidal power supply appears to supply the correct voltage (25.8V) to the power board that it's rated for so I know the power switch in the front is not bad
PROBLEM: Amp will not turn on when cold. Only when I warm it up physically, will it play sound. I use a hair dryer to blow warm air into the vents. One of the pics has a RED rectangle around the suspect area.

* Amp has to be warmed up and the relays click and it starts working fine as new.

* If the room gets below a certain temp normally cooler than normal because of AC it will again click and turn off or click on and off a few times before clicking off for goot until I physically warm it up again.
* Spikes in power also effect the amp. Example when I print and my printer comes out of power save mode, the AMP will click off and then click on. I've tried different outlets, same problem. Same happens when my window AC Unit power cycles.
* I have to keep the amp above a certain temp for it to keep working once I power on via dryer method.
What I have a Tried: NOTE: If you see gunk around some of the points, it's leftover FLUX after I reflowed the points. I probably didn't do as clean of a job cleaning the points as I should have and will if I can fix the amp.

* I took the amp apart to see which parts I need to apply heat to for them to turn on the amp. Using my hot air solder station at lowest temps and distance to concentrate point of heat. I've found this to the right side of the POWER BOARD. Especially over the resistors area. Please see pics.
* I've reflowed solder to all the components in the area with flux and solder and cleaned it up.
* I've heard that could be broken/bad trace. I've looked the board physically, through light, and tested as many traces i could for continuity and I didn't find anything. if it was a trace/temp issue why would a spike in power cause it to turn on/off?
My first instinct was the relays, but then I thought well, they seem to work as intended as they do turn on/off, so it must be something do with power delivery. And the area that needs to be warmed up is also on the POWER BOARD so I just assume it's the power board.

I honestly think it's a some components that likely cost a few dollars and I hate to toss this otherwise great amp and have to dish out more money for a new one. Money that I honestly don't really have, thus the dryer trick.

I'm not an electrical engineer, but I can, am capable and have the tools to replace every part in the amp, I just don't know how to figure out which part? I have a simple multimeter and best I can do is measure voltage, current and resistance. so If you need anything measure, please let me know.

This is my last ditch effort to fix it before I figure out what to do next, I'm just tired of the doing the dryer trick.

Thank you.
viperidae:
You could start with heating individual components, like that dual opamp in the inline package on the edge of the board in your suspect area.
It could have something to do with sensing the power supply has stabilised before turning on the amp board relays to stop the speakers making a popping noise on power on.

aqibi2000:
Go back and address all of the solder points properly, it’s a poorly soldered board

This appears to be a double layer board which could be lacking through hole plating

See the resistor leg
N19htmare:

--- Quote from: viperidae on August 29, 2020, 11:05:58 pm ---You could start with heating individual components, like that dual opamp in the inline package on the edge of the board in your suspect area.
It could have something to do with sensing the power supply has stabilised before turning on the amp board relays to stop the speakers making a popping noise on power on.

--- End quote ---

Thank you, I'll try that and update you. One more point I should add that if the amp is on and working file, and I switch it off and on immediately, it no longer turns on until I heat it up again.


--- Quote from: aqibi2000 on August 29, 2020, 11:34:49 pm ---Go back and address all of the solder points properly, it’s a poorly soldered board

This appears to be a double layer board which could be lacking through hole plating

See the resistor leg

--- End quote ---

I see that, It is through hole and I checked both sides of board. I'm not sure of 2 layer or single but other side has no components.  it seems to be soldered well on the other side, just the solder didn't flow through the hole all the way. But Ofcourse I'll check again and reflow it on this side too.

I need a project so I'll take the board out and post some pics and re-solder clean it up a bit.
ambrosia heart:
 I've found this to the right side of the POWER BOARD. Especially over the resistors area.
If I were you, I would replace ALL components soldered on the power board. :box:
For resistor, read the colour codes and  replace them ALL with same rating and resistance.  Then plug in,
to see if it turns on as usual.   :scared: If not, replace ALL capacitors.

For capacitors, replace them ALL with same voltage and capacitance.Then plug in, to see if it turns on as usual. :scared:
If not , replace ALL diode and zener with same silkscreen marked on their surface.

For diode or zener,  replace them ALL with same silkscreen.Then plug in, to see if it turns on as usual. :scared:

Replacng ALL components is time consuming, however,  worthy. :popcorn:

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