DSW microPRO 3000 amp busted

mpitogo · February 1

Hey so I have two DSW microPRO 3000 and my other one gave out. A few years ago, I had one repaired by Edwards Electronics, they no longer service Polk sub amps (I'm assuming because the subs are too inexpensive and the older subs worth repair are now ancient). Anyway, I'm attempting to repair it myself and it looks like a power supply issue. The NTC Thermistor SCK 048 is busted in the TH1 spot.

. You'll have to zoom in to find it.

This got me thinking. How often do we experience amp separates failures? I've never come across one that has died too young. Of the current power amps I own, they all still work great. I do have a vintage integrated I repaired due to age, it was a 1975 Sansui AU-6900. The amp has a publicly available schematic and knowledgable repair techs who has done repairs before I did mine.

Choices

1) So get that Thermistor and repair it? No guarantee that's the only part that needs to be replaced. Would be nice if a schematic was available. I believe this is the part spec sheet. https://thinking.com.tw/upload/product/files/NTC%20Thermistor-SCK%20Series.pdf https://datasheet4u.com/pdf-down/S/C/K/SCK-1R38_THINKING.pdf

https://reddit.com/r/AskElectronics/comments/k3m8s3/fixing_a_subwoofer_thermistor_alternatives_vs/

2) cover the plate amp hole and get an outboard amp

3) give up on it

My repaired DSW is still running today as a sub for a living room TV with a KEF LSX II LT.

mpitogo · February 1

Looking at the Spec sheet this is the closest part, not the exact replacement.

https://digikey.com/en/products/detail/bourns-inc/BN-LG20Y4R0MYB/19241411

BN-LG20Y4R0Mx

https://bourns.com/docs/Product-Datasheets/BN-LG20Y.pdf

Get a handful as spares and replace both in the PSU I have taken apart.

SeleniumFalcon · February 2

I'll check with a friend at Polk about schematics for that particular amp. I have some general DSW schematics, but not sure how they relate to your model.

mpitogo · February 2

Thank @SeleniumFalcon

I decided to try 1) I ordered a few of the NTC Thermistors and will replace both and go from there. I also have plenty of fuses and will test on a dim bulb tester.

SeleniumFalcon · February 2

I heard back from Tony and, unfortunately, he doesn't have any information on that model. I'm sorry.
One thing to consider is to disconnect the power supply from the rest of the circuitry and see how it behaves after you've replaced the thermistors. Then try and measure the loads the power supply connects to and look for any shorts before reconnecting the supply.

mpitogo · February 7

Thermistors replaced. I tried it without the AMP section. still no go. The new ones are slightly bigger.

Anyway, I inspected the entire power supply board and nothing seemed obviously blown or burnt out. I'd have to go test component by component but I'd rather not. Maybe the best thing for this is just to rip it all out and reinstall the plate with a sheet of no-rez and use an outboard amplifier.

Jstas · February 7

That part is not critical to the sound quality. It is a sacrificial part, kinda like a circuit breaker. If it blew like that it means there's another problem with the amp and that part died to save the rest of it.

Good luck finding what broke or is far enough out of spec to cause that part to self immolate for the greater good.

When my microPro amp bit the dust and I could not get it straight, I reached out to The Speaker Exchange and they had a replacement that worked.

https://reconingspeakers.com/

Might try them.

DSW microPRO 3000 amp busted

Comments