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Discussion Starter #1
The super high quality ASK amp was busted when I bought the car (wasn't a deal breaker for me), and I've finally gotten around to trying to rectify the situation. This will serve as my experimentation log, for anyone interested. If I fail spectacularly, I'll be dumping an aftermarket amp in there assuming I don't set the car on fire, but I figured I'd at least have some fun with the factory setup before I go that route.

1) Removal. The amp itself comes out pretty easily - undo frunk panel holding the tire goo, etc, then slide the metal clip on the left side of the amp out to the left. Pull that edge of the amp assembly toward the front of the car and slide left to remove.

2) Harness. I found a flathead helpful, since the clip on the harness is really tight. Just slide/pry it parallel to the connector's face (straight up when still installed) and it'll come free. Another thing I noticed is that the harness uses rather large, round connector pins for a factory harness. About 2mm across - if going aftermarket, it may be possible to use small "bullet" style quick connectors on the new amp's wiring to avoid cutting the factory stuff, and just plug them into the harness.

3) Investigation. The amp comes apart with half a dozen small Torx screws. There's really not much to this thing. My electronics fu could be a lot better, but it's a pretty sparse board with a lot of big through-board components. Soldering looks mostly doable by an amateur. Did some voltage testing with a multimeter while it was hooked into the car - it's getting voltage through to the speaker outs, but it's low and some of the output channels were reading negative.

After popping it open I found what seems to be the issue - right behind the harness connector, there's a 5404 rectifier diode that zapped on the positive end. There may be other less obvious damage, but I'm starting here. Will update once I get to the local electronics shop and grab some things to desolder and replace that part.


If @ToreB is still around these forums, maybe he's got some hot tips ;)
 

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Discussion Starter #2
Small update since it was late last evening when I looked at this. The solder joints on that diode look like it might have been replaced at some point - the solder itself and the technique don't match up with the rest of the board, though that could be due to the short that killed it heating things up..

Curiously, the thing looks like it may have been installed backwards? IIRC the end with the silver ring should be the negative side, in which case the positive pin is connected to a big ol' trace right off the main ground pin. I wonder if someone's been in here before and just goofed the replacement on that component and gave up after they shorted it. That or the original design had it backwards to act as a sort of ghetto insulator? But again my fu isn't great on this and I can't find a schematic for the amp circuit online so that's just a wild guess.

Top of board, you can see the diode bottom center, next to the first big capacitor. Blackened solder joint on the right side. Left pin is hooked directly to +12v in.

270531


Bottom of board showing more damage to the underside / ground trace running to it. You can kind of make out the difference in the soldering on the less-damaged pin above
IMG_20200908_110423549_HDR.jpg
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Discussion Starter #4
Thanks, @gubi. I actually just found a post from an Aussie porsche forum with the same problem (and board shots :) ) the 1n5404 is indeed supposed to be mounted backwards (see: this link). Theirs got a lot messier when it went, but at least it confirms that it's supposed to be that way. How long the replacement will hold is another thing entirely, but I guess I can get a five pack :p

Gonna go get the resistor and a new solder-sucker here in a while.
 

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Discussion Starter #5
sad trombone.wav

It's still dead as a doornail. Time to break out the multimeter and see if something else is blown. Aftermarket amp is looking like a decent possibility.
 

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If any of those electrolytic caps have bulges on the top it is a sign that the cap got hot possibly from an internal short. Can"t tell from the photo. It looks like that diode got real hot either form itself being shorted or something else on the board shorted pushing a lot of current through it. It should measure about 800 ohms in one direction and open in the other.
 

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Discussion Starter #7
Thanks @MidLifeCrisis. I checked the caps (at least visually) - no leakage, no bulging. The rest of the board is clean as a whistle. Could be something shorted internally in any number of components, but that'll take time to diag.

I checked continuity and voltage to the new diode to make sure my solder was good - I was a bit concerned since the original overheat / short caused the trace running to ground to lift from the board. It still conducts and there was enough pad left I could hold it in place with solder without having to bodge a jump wire in, just looks a little ugly.

Resistance on the diode didn't quite hit 800 ohms - IIRC the measurement was in the 600 ohm range, but was indeed open in the other direction. I can measure again today to verify.

Replacing the diode did do something, at least. Previously, the speaker outs were getting output in the tens of millivolts with some channels reading negative voltage on the positive line. Now I'm getting a solid +5-6v on all output channels but no sound. (I did also check I was getting voltage off the speaker-level input pins...also +5-6v). Didn't think to check amperage on the outs, but I was out of free time last night anyway.

At this point, I may poke around a bit more to see if I can rehab it for sale / keep as a backup and rig up a wiring pigtail for an aftermarket amp, just due to the troubleshooting time involved in going over the ASK board one component at a time being worth about the same to me as a new Class D amp and the hour or so to wrangle wiring. Plus who knows how long it will last if I get it up and running again with stock replacement components.

Another thing I stumbled across, since I've found conflicting answers on the interwebs and it may help others - the remote line (black, red stripe below and between the power/ground lines) should work as a proper remote line for an aftermarket amp.

However it DOES NOT get voltage based on head unit state as one would normally expect. The remote line is hot when the ignition is on and for several minutes afterward. Seems related to the rest of the interior bits that stay powered for a few minutes after the car is turned off and the doors are shut (e.g. interior lights, ability to load CDs into the CD player, that sort of thing). May explain some of the confusion about having to run a wire to a switched fuse in the footwell :)
 

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Discussion Starter #8
Still unable to figure out the ASK's remaining problem(s), so I bit the bullet and installed a small JBL two channel amp instead. Had to cut the factory wiring, as my attempted jerry-rig using 2MM banana plugs into the harness wasn't secure enough, but I left enough spare wire off the harness to re-attach it with spade connectors later if needed. New amp didn't quite fit in the small space allowed for the OEM unit, but it fits perfectly in the spot where the nav DVD would normally go (and I prefer mounting amps horizontally anyway since I can just velcro-tape it down rather than bolting it into the sheet metal). Just had to fish wires up behind the plastic trim above the tire-goo holder.

Of course, it is now that I discover the passenger side woofer appears to be blown <facepalm.gif>. Will swap speaker leads around later to make sure it isn't an issue with the wiring or the new amp, but it sure sounds like the speaker surround is shot on that side.

At least OEM replacements aren't horribly expensive if it does turn out to be the woofer and not my wiring / amp.
 

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If you're getting 5-6 volts on the speaker outputs - there are problems with the output stage. 5-6V is enough to burn out many speakers as you've found - I expect the other speakers may be compromised.

When you say you saw the same on the speaker input pins - I'm guessing this amp takes the speaker level output from the "headunit" (aka radio) and then boosts it to higher wattage?

I wonder what would happen if you hooked up some speakers to the wiring that feeds the speaker-level inputs? You should have a listenable signal there, unless the amp blew up the outputs on the headunit.
 

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Discussion Starter #10
Outputs from the H/U are fine, so far as I can tell - and yes, the ASK amp does take a speaker-level input. One would imagine if the factory amp had fried something in the head unit it wouldn't output sound anywhere, but the midrange and tweeters are working just fine. I thought briefly about hooking the speaker-level ins directly to the door woofer leads to see if I got anything but thought better of it as who knows what the additional load would do to the head unit. Low volume would probably be fine for a quick test but didn't want to risk frying the amp in the CDR-24 as well. Plan on putting a more modern head unit in there eventually, but tearing the console apart isn't on my TODO right yet.

Agreed on the problem in the factory amp likely being in the power / output stage somewhere. I'm thinking it's one of the three 17-pin power amplifier ICs that get clamped onto the case with some thermal goo, but haven't found a pinout for those exact chips yet to guide me where I need to poke at it. The finger-thermometer tells me the one farthest from the wiring harness is dead-cold when powered up for a few minutes (while the other two were noticeably warm).

Fixing the ASK is low priority at this point - going to go out here in a bit and swap the output wires on the new amp to see if the crappy sound follows over to the left speaker. From the sound of it, the right woofer is just dead but it's worth the 2 minutes of effort to verify it isn't electrical.
 

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Discussion Starter #11
Yup, definitely the speaker. Noise didn't follow the wire change, so I'll be tearing down the door panels at some point.
 
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