OPA150 Stereo AMP issues, only turns on when I physically heat it up w/ a dryer! - Page 1
Forum section: electronics / repair

author: N19htmare
author_rank: Contributor
timestamp: August 29, 2020, 09:44:34 pm
content: Amp is a Dayton Audio APA150https://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 badPROBLEM: 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.

author: viperidae
author_rank: Frequent Contributor
timestamp: August 29, 2020, 11:05:58 pm
content: 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.

author: aqibi2000
author_rank: Regular Contributor
timestamp: August 29, 2020, 11:34:49 pm
content: Go back and address all of the solder points properly, it’s a poorly soldered boardThis appears to be a double layer board which could be lacking through hole platingSee the resistor leg

author: N19htmare
author_rank: Contributor
timestamp: August 29, 2020, 11:46:52 pm
content: Quote from: viperidae on August 29, 2020, 11:05:58 pmThank 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 pmI 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.

author: ambrosia heart
author_rank: Regular Contributor
timestamp: August 29, 2020, 11:56:38 pm
content: 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.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.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.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.Replacng ALL components is time consuming, however, worthy.

author: wraper
author_rank: Unknown
timestamp: August 30, 2020, 12:04:31 am
content: Quote from: ambrosia heart on August 29, 2020, 11:56:38 pmIf you are a completely insane psycho who never heard a word "troubleshooting".

author: wraper
author_rank: Unknown
timestamp: August 30, 2020, 12:07:17 am
content: BTW some vias not filled with solder is not a big issue. If solder joint on the other side looks fine and is not cracked, you can just leave it as is.

author: N19htmare
author_rank: Contributor
timestamp: August 30, 2020, 12:16:36 am
content: IMPORTANT UPDATE:Thank you everyone for such informative and quick responses!Alright so I've narrowed it down to the row of resistors and the Diode labled R63 to R75 (In particular R63, R48, R64, R76 and R65) and the single diode ZD6 in between. If I apply heat only to this area, it turns on.I think ambrosia had the right idea, anyone have a easy online tool to identify the line markings?Also for the diode/zener, I don't see any markings, just the black polarity line, I'll check again after removing it

author: wraper
author_rank: Unknown
timestamp: August 30, 2020, 12:32:04 am
content: As it seems from the photos this is purely analog stuff with no digital controls. Relay which clicks should be from output protection circuit. It may fail to enable output because some of the channels have issues, however as it works fine when you manage to switch it on, it's probably not. So IMHO the main suspect is protection circuit. Two boards with a blue Goodsky relay on it seems to incorporate amplifier output stage + protection circuit. Protection circuits probably are interconnected to shut down both channels if abnormal condition is detected on either of them. I would first try measuring output voltages from both amplifiers (before protection relay) without any input signal to see if they are fine (around 0V). You can also try heating one of those side boards at a time to see if heating some particular board allows to switch amplifier on.

author: wraper
author_rank: Unknown
timestamp: August 30, 2020, 12:40:28 am
content: Quote from: N19htmare on August 30, 2020, 12:16:36 amTry heating NJM4560L opamp (U6) with soldering iron. Simply touch it's case with soldering iron for say 10 seconds and see if it allows to switch amplifier on without heating rest of the board.

author: N19htmare
author_rank: Contributor
timestamp: August 30, 2020, 12:47:18 am
content: Quote from: wraper on August 30, 2020, 12:32:04 amWithout input and amp on, I'm not getting any voltage on the outputs, once Ive plugged in the line in signal, that i start getting v.Quote from: wraper on August 30, 2020, 12:40:28 amI have tried that and it is not until I apply heat to the group of resistors next to the opamp that I get it working.Try heating NJM4560L opamp (U6) with soldering iron. Simply touch it's case with soldering iron for say 10 seconds and see if it allows to switch amplifier on without heating rest of the board.

author: wraper
author_rank: Unknown
timestamp: August 30, 2020, 12:52:02 am
content: Maybe try measuring voltage across ZD6 while cold, then measure while heating and see if it changes significantly.

author: N19htmare
author_rank: Contributor
timestamp: August 30, 2020, 02:04:56 am
content: Quote from: wraper on August 30, 2020, 12:52:02 amHere are readings I got at multiple state. Some of the information answers a couple of my prior questions also!.FULLY COLD but with power on the voltage across ZD6 is 9.59V.When warmed up and amp fully working, the voltage across ZD6 is 10.2V.Observation: While the amp is working the votage across ZD6 is constantly dropping. AS SOON AS IT REACHES 9.74V, THE RELAYS CLICK OFF!. The rate of temperature drop is relative to the surrounding temp. If it stays warm enough, the temp will not drop below 9.74V for a while and it keeps working. However if I'm blowing around that area to cool it down, the voltage drops faster.As I warmup the area, the temp RISES and once it's over 9.75ish V, the amp turns on.I think this explains the reason the amp clicks off/on when my printer/ac turn on. I think theres enough Vdrop that it goes below 9.74V momentarily causing the relays to shut off.Bad diode or something else?

author: N19htmare
author_rank: Contributor
timestamp: August 30, 2020, 02:05:42 am
content: accidental double post.

author: wraper
author_rank: Unknown
timestamp: August 30, 2020, 02:14:30 am
content: Quite likely faulty zener diode. Most likely there is marking on the opposite side of it, from which we can figure out its rated voltage. But you will need to desolder it to see the marking.

author: N19htmare
author_rank: Contributor
timestamp: August 30, 2020, 02:28:14 am
content: Quote from: wraper on August 30, 2020, 02:14:30 amit is a either a C12 5T or C12 ST, I can't tell if a 5 or an S. per marking. In case I can't find this exact part? alternatives?The only one I have on hand are 4148ST diodes.I have taken the diode out of the board, is there any way to test it with the meter? should there be any resistance values or anything. a new 4148st diode i have registers 7.75K ohms however when I test the removed diode it registers 750 ohms. does that mean anything?I'm going to try to find all the resistor values and the opamp and just replace everything and see. Wish I could just go down the street and grab a diode but that's not an option for me.

author: N19htmare
author_rank: Contributor
timestamp: August 30, 2020, 05:10:06 am
content: Update: I took out all the resistors and diode.I measured the resistors out of the amp and they corralate their reading with the line markings I checked online, I'm getting new ones anyways.The Diode has a resistance of 750ohm which I'm not sure because the 12C diodes im looking on Mouser do not show that high of resistance value (unless zener resistance is something different). Speaking of which, there are so many 12V diodes that end with with either C12 or 12C... which do I get? Cheap enough to get them all but which do I use?https://www.mouser.com/ProductDetail/Vishay-Semiconductors/BZX55C12-TAP?qs=yIvl1B2wDi6k6fC%252BTXe4cg%3D%3Dhttps://www.mouser.com/ProductDetail/Taiwan-Semiconductor/BZX85C12-R0G?qs=70cth9uAySd1on94GT9WfA%3D%3Dhttps://www.mouser.com/ProductDetail/Vishay-Semiconductors/BZX55C12-TR?qs=WLTup5mM6hjdDCpNA5XDEA%3D%3Dhttps://www.mouser.com/ProductDetail/ON-Semiconductor-Fairchild/BZX85C12?qs=SSucg2PyLi6g04ODt5vpWQ%3D%3Dhttps://www.mouser.com/ProductDetail/Nexperia/BZX79-C12113?qs=me8TqzrmIYXUXVlyPuzVvg%3D%3Dis brand the only thing that's different? am I just looking for C12?Any other parts I should replace while I'm at it that maybe a possible cause? Components are cheap and I'm already paying the shipping and handling.Thanks everyone for your help.

author: wraper
author_rank: Unknown
timestamp: August 30, 2020, 10:08:02 am
content: You partially can test zener diode with multimeter (in diode mode) just as usual diode. It should conduct in one direction. However to measure clamping voltage, you need to connect in to power supply through current limiting resistor and measure voltage. As it seems to be 12V zener, you will need power supply with higher output voltage, somewhere in a range of 15-30V will do the job. As of replacement, any small 12V zener diode should do the job.

author: wraper
author_rank: Unknown
timestamp: August 30, 2020, 10:21:58 am
content: Quote from: N19htmare on August 30, 2020, 05:10:06 amReplacing non faulty resistors is pointless, not to say you can make some mistake when blanket replacing them.

author: N19htmare
author_rank: Contributor
timestamp: September 02, 2020, 10:45:11 pm
content: Alright, little update. Not a good one.I replaced the Diode, all the resistors, and the opamp that you see in that corner along with the two capacitors in that area.SAME PROBLEM!I still have to apply heat which leads me to believe that the board itself could be the cause. They may be a micro disconnect somewhere in the traces and small amount of heat is enough to expand it and connect it until it cools down again.I'm just guessing at this point. I'm baffled.

author: wraper
author_rank: Unknown
timestamp: September 02, 2020, 10:53:45 pm
content: Look where traces from zener diode go. Problem should be somewhere around it. What is the part on small aluminium heatsink?

author: N19htmare
author_rank: Contributor
timestamp: September 02, 2020, 11:15:55 pm
content: It's a c2800y mosfet.I've checked all the traces with a multi-meter and light and whatnot and I just couldn't see anything, if there is a break, it has to be microscopic but a slight change in temp is all it takes. I I think im going to try and find as many points I can around that area and connect them via wire and try to bypass the trace. The fact that the power board solders onto the daughter channel boards, it's a pain in the butt the de-solder and remove the power board.The amp boards to me are placed/design poorly. If you look at the Power board, it screws on to the large aluminum block which is supposed to act as a heat sink for the MOSFETS on the channel boards. However the 4 screws holding the board to the aluminum block are on opposite ends. When screwed into the block, there's basically a tug war going on between the two sides of the power board. The constant cooling/heating of the block has over time caused micro fractures in the PCB. That's my theory atleast.Unless there's a possibility it could still be a different component?

author: N19htmare
author_rank: Contributor
timestamp: September 02, 2020, 11:26:39 pm
content: double post

author: Greyleopard66
author_rank: Newbie
timestamp: August 03, 2021, 07:38:28 pm
content: Did this get resolve? I have problems with (2) APA150 and would like to know your resolution.

author: wires
author_rank: Newbie
timestamp: August 09, 2024, 12:37:02 pm
content: Quote from: Greyleopard66 on August 03, 2021, 07:38:28 pmI had the same issue with 2 APA-150's. After about 5-years, the soft start starts to click on and off and then will fail to turn on the speaker outputs. The issue isn't the zener, it's the capacitor for the soft-start. They use a RC delay on a 220uF capacitor (C37). Once the capacitor reaches sufficient voltage, Q14 turns on the left right speaker relays.In one of mine, C39 had a slightly bulging top (also 220uF) so I replaced it at the same time. That large R79 resistor has heat stains on the bottom of the PCB, so I suspect it's "baking" that capacitor a bit.It's a bit of a pain to de-solder those 4-pin power connectors on the top sides of the board so that you can get it off the amp to work on it. You might be able to grab the cap with pliers, yank it off and tack on a new cap from the top side.I've added a picture to show the parts replaced. C39 was a 220uF/16V, C37 220uF/25V. Just use 25V or larger for both to make it easy.

author: wasedadoc
author_rank: Super Contributor
timestamp: August 09, 2024, 02:11:26 pm
content: Yes, failing electrolytics can increase capacitance when heated.I first encountered that when a colleague asked me to repair his PC that would not power on when the button was pressed. He had googled and found a suggestion to blow hot air from a hairdryer into the fan hole of the PSU for a few minutes. That worked each time.Permanent fix was to replace the electrolytic after the rectifier in the 5 volt standby supply.

author: Greyleopard66
author_rank: Newbie
timestamp: July 13, 2025, 08:34:05 pm
content: Thanks Wires, I just found your reply after my 6th unit failed. I'll start opening them up again.