It should be in ICE but...

Here you can post things about ICE (In Car Entertainment). Like how to install GPS navigation, a DVD-player and other yuppie-stuff. This category might be moved to "those other things" in the end...

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Dan the 480 Man
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It should be in ICE but...

Post by Dan the 480 Man » Thu Feb 08, 2007 6:15 pm

...it hardly gets used!

It's just some general advice really. In my infinite wisdom, i decided to respray my amp to match the bodycolour of the car. Now, it's been reassembled, it powers up, but with a problem. I joined a car audio forum to see if they could help. This is my post:
Dan can't ever just leave things alone 'cos he's an idiot and always ends up breaking things wrote:Idiot of the month award goes to...(def. me)

Now, i have a nice simple but decent sounding system in my car. I've got an Alpine HU with iPod interface, i've got 13cm JBL components front and rear, and a nice Infinty Reference Amp (7521A) running an Infinity Reference 12" Sub. It's a really nice sounding setup, and by far the best sub/amp combination i've had.

I had a pretty basic install-amp covered up and sub on show in the boot. However, i wanted to 're-do' the install. The first thing i wanted to do was colour-key the amp's metal surface to match the car's body colour.

So, armed with a screwdriver, i took my amp apart. I carefully removed the necessary screws/covers/wires, and i photographed every single step so i knew how thing's went back together and where they go.

One nice white amp later, it's back together-everything as it should be. However, although the unit powers up, anytime i try to adjust the levels (bass boost, mhz etc), the unit sparks at point of contact (e.g when the screwdriver touches the adjuster knobs). Now, it appears to be happening when the screwdriver touches the outercasing of the amp at the same time as the adjuster knob. If i get a tiny screwdriver and it only touches the adjuster, then it's fine. However, during playback with the system turned up, every now and again the sub will 'pump', as in just a random thud. Only lasts about a second, but it's doing it-which is annoying. Now, unless i'm being thick-it seems like an earth problem. But my GND wire is fine-it hasn't been distubed at all.

I wish i'd never taken it apart now, as i fear a new amp may be on the cards. Is there anything i can do to solve the problem? Is there anything i should look for on the circuit board or is it well and truely shagged??

Any advice (other than 'don't take your amp apart in future' lol) welcomed with open arms!
So, that was the initial post. Some responses, but as it's a popular forum it's soon forgotten about and disappears off the first page.

Now, the black wire inside the amp is connected as it was when it came apart. The GND inside the boot is fine. The only other thing i can think of is this:

In the pic you can see these little black square thingy's (i don't know what they are). They are sitting on some rubbery paper thin strips that look like plasters. One plaster thing was midly 'nic'd' when i was prising the black square things off. However, it wasn't like crowbar prising, it took a 0.5mm flathead screwdriver to just 'ping' them away from the strips. They were stuck onto the strips with something, but not alot-maybe just some spray adhesive? When i put the amp back together, i bent them down ever so slightly, so they would press up against the case to ensue a good contact. As the rest of the circuit board is intact, no 'chargrilled' marks anywhere, i'm thinking this may be the cause. I'm just wondering in the mean time wether anybody has had any similar experience or could give me some things to test at the weekend. Two audio centres have told me that most of the time amps are just dumped 'cos it's cheap enough to buy a new one. I've seen mine again from a dealer, but it's still £80+, so it's money i don't have.

Anybody any ideas/advice?

Oh, and the pic...

Image
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Post by hailesmail » Thu Feb 08, 2007 8:16 pm

The paper thin rubbery strip does two jobs, firstly it insulates the metal back of the transistor from the body of the heatsink it's bolted too, secondly it conducts heat from the transistor to the aforementioned heatsink where the surrounding air removes the heat.

If it is nicked you may get an arc to the case which will eventually blow the transistor completely, but in the meantime may give the symptoms you describe.

The substance you thought was adhesive is actually heatsink compund, a silicone based paste that when smeared on thinly enough improves the heat transfer.
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Post by pol » Thu Feb 08, 2007 9:04 pm

It does look like thermal compound / tape to me too. Try insulating those transistors? Looks like they must get hot if they're fixed in this way? Maybe get some more termal tape and re seat those transistors? Just suggestions mind..

pol

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Post by Murf » Thu Feb 08, 2007 10:14 pm

Agree with the above!
If its not that theres a slight chance youve damaged some components with static when you removed the case but its much more likely to be a transistor shorting to earth.
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Post by Dan the 480 Man » Thu Feb 08, 2007 11:43 pm

Cheers guy's...

Already way more helpful than the Talk Audio forum. So, i've just been looking on eBay, just to have a look at thermal compound and nearly all the results turned out stuff like this. Would this be the sort of thing i'm looking for?

It appears to be a paste (clever aren't i? :lol:)-so does that mean i need to replace the rubber strips too? Sorry if they're daft questions, i just wanna fix me amp :(
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Post by hailesmail » Fri Feb 09, 2007 9:12 am

That compound will do fine, but you will need the rubber insulator as well, that will be harder to get and you may be easier getting a shop to fix it for you to be honest.

Or if your feeling brave you could get these and modify one of them to fit....

http://cgi.ebay.co.uk/T03-SIZE-TRANSIST ... 0078010436
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Post by Dan the 480 Man » Fri Feb 09, 2007 5:48 pm

Hi.

Thanks for the info. I've been having a look across the internet to see what i can find, and i found these, aside from your ebay result earlier:

Item 1
Item 2
Item 3.

I can't figure our what size T03 is, which is why i thought about item 1. which would be the better of the two, if any-or which would you try. I'm prepared to take a gamble!

I've called as many local car audio dealers as i can find so i can run it down on my day off, but so many just aren't interested in repair. All they want me to do is bin it and buy another amp. I don't want to do that, i want to have a go repairing first!

Any advice greatly appreciated! :D
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Post by hailesmail » Fri Feb 09, 2007 6:02 pm

The links didn't work complained I didn't have your cookies.

However the item with Part no.: 189251 - 62 looks like its probably what you need.

T03 is about 1.25 inches x 3/4 inches by the way, it's used in the line output stage of an older TV set amongst other things.
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Post by Dan the 480 Man » Fri Feb 09, 2007 6:20 pm

The linls aren't working for me either.

This is the one i first thought when browsing, and it's the one you also suggested, so looks ok...

Image

I'll be ordering this tomorrow with the adhesive stuff, so hopefully a repair is on the way! Thanks for your help so far...i've learnt my lesson!
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Post by hailesmail » Sat Feb 10, 2007 10:53 am

Good luck :)
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Post by Dan the 480 Man » Mon Feb 19, 2007 5:15 pm

Well...

I got the stuff-adhesive compound and the thermal tape. Cut and measured everything, smeared the compound onto the transistors as well as the tape and secured everything. Put all the amp back together.

Took it to the boot just now, wired it back in, turned up the CD player, and what was i presented with? Nothing. So i looked at the amp, the light was on, the protect light was off. aah, all the levels were turned down, so i took the screwdriver, turned the amp's gain up....and....not a spark, nothing! :D The 'boom boom' was back! :D

So, i'm going to keep my eye's on it for a few days, but it would appear that at this moment in time, it's fixed (and hopefully it'll stay that way touchwood!)

Cheers for the help guys! :D
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Post by hailesmail » Mon Feb 19, 2007 11:24 pm

Well done :)
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