P38A dsp amp repair

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biketeacherdave

biketeacherdave

Well-Known Member
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south east london
2015-11-27 21.39.27.jpg
So my own DSP amp has started giving me problems iv managed to narrow down the problem I think using thermal shock to the micro chip under the black protective coating but for good measure I'm going to swop out the plug in chip for the rear speakers just in case its that, thermal shock isn't exactly 100% accurate with components this close together must get a new can of freeze spray in the morning.

Moving on tho Carl on here very kindly sent me his duff DSP amp shown here in the photo his symptoms are completely dead amp I plugged it into my car to confirm my amp has hiss on the rear speakers which does go after a while.

Its a basic circuit clearly seen the bit with the gold square around it is the amp power supply which splits into 2 circuits front and rear then those in turn into left front,right front/left rear,right rear. The 4 main amp power ICS on mine get hot as they should they use the ally protective causing as a heat sink on Carl's circuit board these are cold indicating no current draw, I would imagine the power supply has failed so with the absence on a circuit diagram I'm going to draw my own to see where the power goes, I will also get the meter on it tomorrow once its connected again on both circuit boards and do a voltage comparison.

There mite be some hope for those of us with the HK DSP amps if I can get either one running 100%.View attachment 93368
 
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Dave, that would be awesome if you can repair these amps. They are not cheap from the main dealer. £550+vat last time i checked and it's a non stock item they order it.. you buy it first and no returns.
 
That's the plan mate should know by the end of next week if its doable, also gotta come down n fix those heated seats for you will prob have a day free Thursday/Friday examiners are striking.
 
Watching this with interest.. have one dead one in bits, and another which is as-yet untested.

Gave the board of the dead one to my dad who's an electronics tech by trade, and looked at it with him the last time I was home (about 3yrs ago!). He managed to find that the power supply seemed to be working, and that the amplifier chips themselves seemed to be in some low power mute mode - which seemed to trace back to the chips under the black blobs. So even though we could measure power voltage at the amplifier chips, they weren't actually switching on because they weren't being enabled by the chips that drove them.

Interested to see what the thermal shock does to the covered chips, we came to the conclusion the problem was something to do with them, and that chances are it wasn't a simple fix!

Not sure if any of that helps you, but will be keeping an eye on this thread for any progress :)

Marty
 
Hi Marty

Yes the chips under the black protective coating seems to be the problem on my amp oddly I suspect the coating to be the cause of the failure the heat sink for these chips is mounted under the board a poor design in any ones books.

I'm working out the power supply diagram slowly the one I was sent seems to be faulty power supply. I have to do a lot of the testing sitting in the back of the car not ideal as the weathers bad so need good weather. After a bit more thermal shock on my own amp I will know for sure if its chips under the coating or the plug in ones. Plug in ones can be swopped out for known good ones, power supply is fixable chips under the coating properly not.
 
Interested in this as my amp has partly failed. The front speakers work and the cd changer so have some radio. All the controls work but the rears and the subwoofer just have a horrible sound so have removed the rear speakers and subwoofer until I can find a replacement amp or fix.
 
Well I will keep you updated due to the recent wind n rain iv not been able to sit in the boot tracing voltages for my own amp to compare with the duff amp but have drawn out a circuit diag for the power supply.
 
Actually you cannot buy these new any more from LR at any price. I know as I tried and was told simply they are obsolete. Also http://www.gb4x4radios.com/uk.html (formerly Roverville) say they cannot be repaired because components are not available.

I got one from e-bay that was advertised as being new. Sent Dave my duff one to see if he can work a miracle.
 
Lone_Wolf said:
Actually you cannot buy these new any more from LR at any price. I know as I tried and was told simply they are obsolete. Also http://www.gb4x4radios.com/uk.html (formerly Roverville) say they cannot be repaired because components are not available.
I got one from e-bay that was advertised as being new. Sent Dave my duff one to see if he can work a miracle.
Click to expand...


and very greatfull i am for it to if i can identify the chips then it can be repaired but got to get the protective coating off first i suspect all these amps share the same chips so if i can amass a collection of duff amps i should be able to get some of them going, this one is defo a duff power supply just need a dry day to sit it the back of the boot for a couple of hourse.

so if any one has a duff dsp amp sitting around il gladly take it and see if i can either fix it or strip it for parts
 
Well its taken me 2 years to get back to this my own amp is still working all beit with a hiss from the rear speakers and other things with the car have kept me busy.
Loan wolf sent me a dead amp to try and fix.......
SO i took a different approach sat down and had a long good look at the pcb and found it !!!! Yep found the bloody fault the component iv marked with the red ring has burnt out all i need now is another dead amp so i can swop it out and test it.

Any one got one laying in there shed ???
20171117_212211.jpg


Will pull my own amp tomorrow and compare metre readings and see if this component looks the same on my amp pcb i cant remember if my previous photo in my post was my amp or not am thinking it was so conponent looks the same
DOH !!!!
 
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Fascinating thread Dave. Every time I turn my radio on I have a moment of "is today the day it goes pop?"
My car's already had one factory new DSP amp, back in around 2010, so if the first lasted 8 years, the current one hasn't long to go. I've got the even more obscure 17 speaker setup with Nav, which needs an even rarer DSP amp. On the odd occasion they come up for sale "used- good working order" they're advertised for between £400- 600. Originality is important to me, but that's expensive originality.
So- what is that component you've highlighted? Any idea?
 
Orangebean said:
Fascinating thread Dave. Every time I turn my radio on I have a moment of "is today the day it goes pop?"
My car's already had one factory new DSP amp, back in around 2010, so if the first lasted 8 years, the current one hasn't long to go. I've got the even more obscure 17 speaker setup with Nav, which needs an even rarer DSP amp. On the odd occasion they come up for sale "used- good working order" they're advertised for between £400- 600. Originality is important to me, but that's expensive originality.
So- what is that component you've highlighted? Any idea?
Click to expand...

I can not identify the component i began drawing my own circuit diag 2 years ago mapping out the power supply but after a very long time gave up trying to repair mainly because these components are micro size with no identifying marking.

However on this part of the pcb there are x4 circuits using the same components the suspect faulty part is in the 1st curcuit and reversed. It reads totally different to the other 3. I will need my pcb in front of me for a comparrison.
If my amps dies completly then im gonna rip it all out and retro fit something, i would prefer it to be standard tho.
 
It is a zero ohm melf case resistor will still need to do a measurement comparrison to my working amp as im getting a reading of 900 ohms both ways so its not o/c
 
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biketeacherdave said:
Well its taken me 2 years to get back to this my own amp is still working all beit with a hiss from the rear speakers and other things with the car have kept me busy.
Loan wolf sent me a dead amp to try and fix.......
SO i took a different approach sat down and had a long good look at the pcb and found it !!!! Yep found the bloody fault the component iv marked with the red ring has burnt out all i need now is another dead amp so i can swop it out and test it.

Any one got one laying in there shed ???View attachment 135161

Will pull my own amp tomorrow and compare metre readings and see if this component looks the same on my amp pcb i cant remember if my previous photo in my post was my amp or not am thinking it was so conponent looks the same
DOH !!!!
Click to expand...

Dave, talk to @martyuk. He's played extensively with these and even got as far as a replacement kit. I'm pretty sure he might have one in his shed or be able to confirm the components that failed on the ones he's seen.
 
I've got 5 DSP amps at home at the moment, 4 of which are faulty and don't fully power up - I started tracing from the back end at the amplifiers and found that the amp chips are being held in standby on the faulty ones.

I've had a look through the standby circuitry for the amps and it all SEEMS to check out, and the inputs to this come from under one of the black blobs.

I tried removing the plastic from one of the DSP chips under the blobs, and just ended up destroying the chip - so I have one amp which is not totally unrepairable.

The bad news... I'm away out of the country on and off with work until pretty much the New Year, so don't have access to my collection of dead amps to even be able to compare notes. (though I think we definitely should once I'm back).

The component you circled though is a Zener diode - and they come in different voltages, so would need to work out what value it is and get a suitable replacement. Can you get a close-up of the component? some Zener diodes do have a black stripe on them which can make them look like they are burnt out - but I'm also hoping that it might give some clues into finding a replacement.
 
Zener diode make sense, I'm sure there must be a common component that fails on these boards this one won't power at all, i have been taking component reading of the power supply I'm getting reading of over 20meg on one surface mounted resistor and I just cant see that being correct for such a low powerd circuit board.

Will know once iv pouilled mine and do a comparison
 
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When I get back home for more than a couple of nights before heading out the door again, I'll pop open the working DSP amp that I have and then will try and get some measurements on the board around that component from the working one, and compare that to one of my dead ones - and also see if I can garner any information at to what value the Zener diodes are. Sometimes they have a couple of numbers written on them, and I can look them up in a SMD component handbook to identify them aswell...
 
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