Who can repair a home audio circuit board? Polk powered sub died

bored350 · Aug 29, 2019

I have a Polk DSW PRO 500 powered sub that runs as part of my garage stereo. It worked until I shut everything down a few days ago but won't power back on as of yesterday. Google research says its common to loose a diode, resistor and sometimes (1) IC. My visual inspection says at least 1 or 2 of the resistors on the incoming AC power circuit are burnt along with a diode.

Can any of you fine gentleman assist in diagnosing/repairing this unit? I've been more than pleased with it to date and really would prefer to fix it but the $250 Polk wants for a new amp is just too rich for me.

Pic borrowed from an online search, but my board with bad diode looks almost identical to the one seen at the bottom.

197997_52898325_321633155366280_218569631562989568_n-jpg.145419

SGKent · Aug 29, 2019

It is a dead industry. There are those of us who fix our own things but we don't do it much for others. The general rate per hour these days for any kind of technician in any industry runs somewhere from $50 hr to $250 hr. Even if someone has 5 hours in troubleshooting the polk then that is $250 and parts. The consumer walks away at that price. Just because the power supply is bad it does not mean that something downstream from it didn't fail and take out the power supply. I worked on a TV for a friend once an 14 transistor circuits in a row failed because one diode went bad. I'll bet you'll have $750 in repairing that if you are lucky. Sorry to be the bearer of bad news. Find a friend in his 60's or 70's that did that kind of work when he was in his 20's and still has a lab and equipment, and you'll find the person you need. 2007 was not a good period for electronic equipment. Some of the stuff made in that period began to have layered circuit boards where the traces are on multiple levels.

If I had to guess, the two big capacitors are leaking out the bottom and that failure caused other issues. And - in some cases you can't even find the integrated circuits anymore because they were proprietary. C8 might be swollen too.

EDIT: I looked online to see what could be found and there are a lot of people with Polk amps of that model and similar who have had the same experience as you. When they called Polk to see what to do a typical response was you can buy a new amp for $375 for that unit. That was a couple years ago For what it is worth, you can find a good new amp at that price with a warranty. One guy bought a couple capacitors, new diodes, etc replaced them and when he turned the switch on they burned out again.

My credentials are that I ran two regional consumer electronics repair centers for Teledyne in the mid 1970's. I have friends who still do that sort of thing when they are out of things to do but nothing they take in on an ongoing basis because they could never bill out at a reasonable labor rate, which is really below minimum wage on most jobs like that.

yeldogt · Aug 29, 2019

I feel you pain .....

Try E-bay ... it's a fine line. Common failure on an expensive product -- sellers often want too much. Reverse often has no market and you can't find anybody selling.

I have been lucky on items I never figured I would find.

californiaHank · Aug 29, 2019

I agree with pretty much everything Merlin said in post #2. I repair interesting/vintage/classic/rare audio equipment as a hobby, mostly for fun rather than profit. It's seldom worth the time and effort to do component level repairs on modern consumer equipment unless it's something really exotic or rare.

The offer you got from Polk for a $250 replacement amp is probably the best you're going to get. By the time a professional tech diagnoses the problem, identifies all the parts that were collateral damage to the original failure, obtains replacement parts, and installs them, the bill is going to be bigger than the repair is worth. It's not the kind of repair you can figure out just by looking at pictures of the board - you've got to get hands-on with it - making measurements and probably desoldering some parts for testing. It likely makes more economic sense to just swap in a new amp for the failed one.

inphx · Aug 29, 2019

Find your receipt and check credit card to see if it has a 2x warranty feature. Polk audio replaced the circuit board under warranty for me.

OldSoldier · Aug 29, 2019

I had a powered sub that stopped working, so I cracked it open and found a burned out resistor. I replaced the resistor and it started working again. I did this work at least five or six years ago and it still works fine. My total cost was about 10 cents and time. Since then I've had to recone the speaker as well since it tore the surround. If you can't afford the new amp, identify the burned out components and try replacing them. If it doesn't work, then you can save up for the replacement and all you're out is the few bucks for the attempted fix.

sberry · Aug 29, 2019

We could take a look if you want to mail it.

Fasthotrod · Aug 29, 2019

Just throwing this out there... but you might be able to get an aftermarket sub amp to drive it instead. Perhaps one of these has a similar size/shape:

https://www.parts-express.com/cat/subwoofer-plate-amplifiers/332

If not, then an external amp might be the way to go instead:

https://www.parts-express.com/cat/power-amplifiers-live-sound/346

Hope this helps.

Mark

exmaxima1 · Aug 29, 2019

Fasthotrod said:
Just throwing this out there... but you might be able to get an aftermarket sub amp to drive it instead. Perhaps one of these has a similar size/shape:

https://www.parts-express.com/cat/subwoofer-plate-amplifiers/332

If not, then an external amp might be the way to go instead:

https://www.parts-express.com/cat/power-amplifiers-live-sound/346

Hope this helps.

Mark

The Polk amp has a room optimization feature that the aftermarket amps do not have.

SGKent · Aug 29, 2019

exmaxima1 said:
The Polk amp has a room optimization feature that the aftermarket amps do not have.

only when they work

MBfreak · Aug 29, 2019

OP.
The two large caps are probably glued to the PCB, what somebody has diagnosed as leaking caps.
The two diodes around the U1 Ic have overheated but may still be OK.
U1 is most likely a chopper that supplies a square wave AC voltage ( at many kHz)to the step down transformer ( big yellow taped component)
Above that is the several LV rectifiers and caps that supplies LV DC to the unit.
This switch mode power supply is a lot cheaper than a 60 Hz transformer unit.

It is probably quite easy to repair IF it is the power supply that is faulty.

If you do not mind sending the PCB to Sweden, please PM me for adress.

If you attempt to fix it yourself be a bit careful. The two big caps ( black cans) roasted diodes, transformer and IC operates at around 180 VDC and are galvanically connected to the mains voltage thru a full wave rectifier.
Lethal voltages.

Ola

MBfreak · Aug 29, 2019

If you are comfortable to measure on energized parts here is a tip.
Disconnect from mains and look around PCB outputs from the power supplies, they often have plug in leads , marked up with correct voltages ( like +5 V, + 12 V, -12 V etc) on the PCB

Get test leads that can reach the live part of the connector or measure on back of PCB.

Power up and see if the voltages are correct.
Also
Quite often the mfr has deleted the mains switch and has one small power supply running the remote ctrl input for on/off. Energizes 8600 h/year so caps age much faster than parts on only when you switch on.
It is enought that a $ 0,5 cap in that " always live" low power supply gives up life, the rest of the board may be perfectly OK, even if it looks a little bit sun-tanned.

best regards , again,

Ola

CoogarXR · Aug 29, 2019

I had two JBL powered subs given to me that had blown plate amps. I just took the amp out, cut a board to fit the plate amp hole, and installed standard speaker connectors. Then I drove them with a standard outboard amp. That's the easiest/cheapest thing to do.

bored350 · Aug 30, 2019

I appreciate everyone's feedback. To clarify my original post, I am not interested in retrofitting an aftermarket amp to this system or using an external amplifier either.

Sberry and MBfreak, I appreciate your offers to help; I'll be sending each of you a pm in a few minutes.

MarvinBerry · Aug 30, 2019

That picture really doesn't tell the whole story.

To figure out any chances of repair we'd need to see the backside of the board which has the circuit traces themselves, see what's left or...if they lifted when it burned.

Even if the traces lifted it'd be fixable but quite possibly not worth the cost vs struggle. Sending the board alone for repair probably isn't enough, someone would likely need the whole sub itself and cost of shipping etc makes it along run for a short slide.

On the flip side, this might be a perfect time to buy a cheap soldering iron and dig in. Not a hard skill to pick up and it's not like you can break it more, it's already broken!

James-W · Aug 30, 2019

What you need first is a factory service manual for it. Depending on what is wrong with it, parts may or may not be available. Parts like capacitors, diodes, resistors, etc, are not usually a problem to get from any electronic parts supply store. Sometimes getting a specific IC can be a problem. A lot of times if the OEM IC is no longer available, you can cross reference the part number and come up with something that will work, but that is not always the case.

MarvinBerry · Aug 30, 2019

The burnt IC is an 8 pin, can't read the markings but probably something basic like a TL071 or 5534. Lots out there & easy to substitute.

Believe it or not but resistors & diodes are much harder to source these days. Most everything has moved away from larger through hole components to small surface mount.

You'd have to find someone with a stash of parts. I have em, not that I'm volunteering to fix this thing...

MBfreak · Aug 30, 2019

The U1 8 pin DIL is most probably a switching regulator chopping the app 170 VDC to a square wave at sevaral 10´s kHz that is the transformed down by the ferrite cored transformer, covered in yellow tape.
If so , U1 is definitely available at any good component supply company, there wer only 4 main line manufacturers and nobody would have developed a proprietary unit.
Mass volume part several hundred millions made.
Can you read the type on the U1?

Ola

foolishpride · Aug 30, 2019

Contact Terry at D-Lab Electronics. He can fix it.

https://reverb.com/shop/d-lab-electronics
[email protected]

engineer2 · Aug 30, 2019

If it's a common issue with these, search ebay for a repair service.
I had a Panasonic TV circuit board go out (with a loud bang). Apparently a common issue that takes out about 4 components. I found a guy on ebay who repaired it for $75 with shipping. It's been working fine since.

bored350 · Aug 30, 2019

Just to reiterate, the pic attached to the original post is not from my amp, it is from the internet.Now that I have access to the amp again, I am able to take a look at it in a closer light. I have identified another possible bad component based upon heat marks in the board (p/n CQ1265RT). I am attaching a few pics for everyone's perusal, sorry, no way to resize them from my phone at this time.

MBfreak, the info on U1 is KJD647

mobiledynamics · Aug 30, 2019

I've been the same/similar boat. Have a $5K sub with onboard amp....hardly ever used, getaway home. Drivers are fine. It's on the onboard. It's not worth my ROI for me to send it out to get it repaired, but eh, maybe one day I'll change my mind.

starckie · Aug 30, 2019

If Polk will sell you a complete amp shipped with a warranty for $250 I would jump all over it.

You could see if it is common problem on Club Polk (polk audio forums) or try calling Soundscape in Baltimore MD (a long time Polk Audio dealer) but honestly, by the time you consider your time finding someone, paying to ship to and from a repair shop or person, labor, parts, the risk of another failure (because the root cause wasn't fixed or other parts are weakened) I just don't see where you are going to save a massive amount of money.

I was a technician in the 90's and even back then that would have probably been a $125-$175 initial estimate (to account for troubleshooting/parts/labor/unknowns once initial issue was fixed).

foolishpride · Aug 30, 2019

Component U1 is an 555 Timer IC. The chip can be used as an oscillator or a timer. You can get a replacement here for that, and the diodes that look burnt.

https://www.parts-express.com/lm555-timer-ic-(8-pin-dip)--lm555

MarvinBerry · Aug 30, 2019

Like I said you'd need to yank the board off and see if there's anything left of the traces first... if they've lifted pony up for the replacement board. Looking at a pic of the top side offers zero info. Sorry.

If the traces are still there its a prime candidate for DIY. The parts are cheap, labor is expensive unless you can supply it and soldering is a good skill to have.

Soldering 101. This is for guitars but same ****.

https://www.premierguitar.com/artic...DZJfSVNWIpa5gL5C6UgwPT63-N-mCGguEL5HUGTydVFQ4

outdoorspace · Aug 30, 2019

U1 is a ST Micro VIPer part. The number you posted looks like a lot code and not the actual part number. What are the numbers after VIPer?

Your diode seems to have a vaporized lead? It's a TVS diode, maybe used as a snubber. P6KExxx where *** is the voltage rating.

I'd guess other parts nearby have failed as well.

bored350 · Aug 31, 2019

outdoorspace said:
U1 is a ST Micro VIPer part. The number you posted looks like a lot code and not the actual part number. What are the numbers after VIPer?

VIPer12A

@MarvinBerry, I didn't have any tools handy when I took the pics, should get the circuit off the mount tomorrow and take some additional pics.

Sent from my Moto G (5) Plus using Tapatalk

James-W · Aug 31, 2019

What you really need to repair it is a service manual with full schematics. Without a service manual you can only guess, with a service manual you can troubleshoot it down to component level. Seriously, try to get a service manual for it. It will give you schematics so you can troubleshoot the board and it will give you part numbers for all the components.

outdoorspace · Aug 31, 2019

https://www.digikey.com/product-detail/en/stmicroelectronics/VIPER12ADIP-E/497-5575-5-ND/1040563

That VIPer has an integrated switch, so that makes things easier.

You'll need to pull that diode to read the full part number. When you go to order replacements get a couple of everything, if other things are still bad your new components will likely go **** the first time you switch it on. :shocking:

The bottom side may have blown components too, or damaged traces as mentioned before.

zeke67 · Sep 4, 2019

I agree with most of the posts already. It's dying art, it's too much in labor $$ to take it somewhere, components are hard to find now, and so on. That said, if you can solder or are comfortable trying to learn, you can fix this. You don't need a schematic to identify parts. Look for burned areas, which I think you have done already. And look for leaking capacitors (i.e. caps). They can swell but not leak. If you have one leaking cap, replace all. Most diodes, caps, resistors, transistors and small ICs are common parts that used to be easily found at Radio Shack. Fewer Radio Shacks makes it hard to get parts. However, on line places like DigiKey, and stores like Fry's (if you have one) are sources. And very cheap. You may very well pay more in shipping.

Also, and maybe most importantly, most common problems are VERY well documented on You Tube now. And possibly, there are e-bay or Amazon sellers that make kits to DIY fix the common problems. Case in point, my 10 year old Sharp TV has a very common problem with 14 caps leaking. Lots of videos on how to desolder the old and install the new. My biggest pain was taking the thing off the wall, opening it, identifying the caps, ordering and waiting (no Radio Shack anymore) and living without the TV for a week. I found a seller on Amazon that had the parts, solder and related sundries. It was about $15, way more that the value of the parts. But it was all there and i was done in about an hour start to finish. I did all of them in spite of how they looked.

To be fair to some posters, a schematic is useful. Other components can fail downstream. Seeing burnt marks isn't the truly correct way to measure if a part is bad. But you can skip by these points by spending a few bucks and watching a few videos and if you can't fix it you end up with the alternative you started with -- buying a new one. Good luck and post results.

James-W · Sep 4, 2019

zeke67 said:
You don't need a schematic to identify parts. Look for burned areas, which I think you have done already. And look for leaking capacitors (i.e. caps). They can swell but not leak. If you have one leaking cap, replace all. Most diodes, caps, resistors, transistors and small ICs are common parts that used to be easily found at Radio Shack. Fewer Radio Shacks makes it hard to get parts. However, on line places like DigiKey, and stores like Fry's (if you have one) are sources. And very cheap. You may very well pay more in shipping.

To be fair to some posters, a schematic is useful. Other components can fail downstream. Seeing burnt marks isn't the truly correct way to measure if a part is bad. But you can skip by these points by spending a few bucks and watching a few videos and if you can't fix it you end up with the alternative you started with -- buying a new one. Good luck and post results.

With all due respect, a schematic diagram with a parts list (service manual) is essential to identify parts. You have a burned up resistor. Without a schematic, what value was the resistor? You have an IC that you suspect is defective. Without a schematic, how do you know what the correct voltages should be on the different pins? Without a service manual, the odds of a novice fixing electronic equipment is not all that good. If you happen to be an electronic technician who is VERY familiar with a certain model of equipment, then you have a fairly good chance of repairing it without a schematic. But even then, a schematic and a parts list with part numbers is your best friend.

californiaHank · Sep 5, 2019

Maybe the TVS diode failed like the original example the OP got off the internet.
Maybe it also took out R4 when it failed, or maybe it didn't.
Maybe it took out other components, too.
Lots of fun to speculate, but a complete waste of time if you don't have the board on your bench and your DMM handy.

outdoorspace · Sep 5, 2019

A schematic won't hurt but it's a luxury and I doubt it will be made available. Usually it's possible to figure out what values are needed by understanding the circuit. Nearly everything I have repaired did not have a schematic.

In this case I'd shotgun it with a few parts and see what happens.

American Locomotive · Sep 5, 2019

Yup, just order some jellybean parts from Digikey (like those diodes, IC, etc...) and shotgun them in there. Especially if this is a known and documented problem with a solution.

One thing I would check however, is the dark brown glue holding various components down on the board. In my experience, that glue doesn't start out as dark brown - usually yellow. A lot of these glues used on electronic circuit boards have this weird problem where they actually start to become conductive as the age. It's easy enough to check: put your multimeter on resistance (100k or megaohm range if it's not auto-ranging) and then stab the glue with both probes. Keep the probes about 1/8 - 1/4" away from each other. If it reads any conductivity at all, you'll need to carefully scrape the glue off.

zeke67 · Sep 5, 2019

James-W said:
With all due respect, a schematic diagram with a parts list (service manual) is essential to identify parts. You have a burned up resistor. Without a schematic, what value was the resistor? You have an IC that you suspect is defective. Without a schematic, how do you know what the correct voltages should be on the different pins? Without a service manual, the odds of a novice fixing electronic equipment is not all that good. If you happen to be an electronic technician who is VERY familiar with a certain model of equipment, then you have a fairly good chance of repairing it without a schematic. But even then, a schematic and a parts list with part numbers is your best friend.

Read again my second paragraph. I read resistor values from the color code. Capacitors are typically stamped, at least the electrolytic type that commonly fails. For parts swapping an IC, you don't need to know voltage values, just a part number. Google is useful for cross referencing a proprietary number to standard number (assuming an IC exists.) Logic ICs voltages are state dependent.

American Locomotive · Sep 5, 2019

zeke67 said:
Read again my second paragraph. I read resistor values from the color code. Capacitors are typically stamped, at least the electrolytic type that commonly fails. For parts swapping an IC, you don't need to know voltage values, just a part number. Google is useful for cross referencing a proprietary number to standard number (assuming an IC exists.) Logic ICs voltages are state dependent.

If the resistor is burnt up, or an IC has a hole blown it in, you will not be able to get part numbers.

Ultimately, both you guys are right. Schematics are an extremely useful and important diagnostic and repair tool - especially when you have blown up components. However, most consumer electronics generally pretty simple (at least on the power-supply side of things), and can be repaired with just basic electronics knowledge. Components like through-hole resistors and capacitors are so cheap that it's not a big deal to just buy a bunch of parts and shot-gun replace all of them.

Sevenhills1952 · Sep 5, 2019

Where are you located? You could contact NESDA (Fort Worth Tx.) or ProSquad, both organizations have lists if qualified service technicians maybe in your area or could mail to one for repair.
Consumer electronics repair is not as easy as you think.

Sent from my SM-S320VL using Tapatalk

nlujan85 · Feb 6, 2025

PolkAudio Pro 660
where can I find replacements for these resistors...

wyliesdiesels · Feb 6, 2025

mouser electronics?

PCustoms · Feb 6, 2025

wyliesdiesels said:
mouser electronics?

Digikey
Arrow

Etc.

Falls into if you have no idea where to buy the part, so you really have the skills or tools to change them?

Also 5+ year bump for a barely related new post.

Who can repair a home audio circuit board? Polk powered sub died

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