My 500.4 needs some help

winno · Post by **winno** » Fri Mar 08, 2013 2:53 pm

Hi everyone.

My 500.4 has an issue with one channel - front left. The issue exists in bridged and un-bridged modes.

Outline;

*When the amp is cold, it's fine.
*After its warmed up though, the driver connected to this channel pops now and then (regardless of the volume).
*It also sounds distorted now and then as well.
*The driver seems to 'wobble' in and out a lot more than its supposed to (similar to home speakers being run off a turntable with bad mechanical isolation - rumble).
*The driver cone also seems to only be pulled into the basket from resting position on bass notes rather than a combination of push and pull. It seems like the amp is only producing one side if the sine curve(?).
*When I switch the amp on when its already warm and before the TAIM muting switches off so music can be heard, the cone is sucked in a little. Switching things off sees the cone let go so it can go back to resting place.

It's only one channel. I've tested the other channels through playing them through the same driver - all good.
I've also popped in a spare 475Ti to replace the 500.4 and no issues.

A local Technician has looked at it. He's an ex PG and Alpine tech. He's confirmed there is a problem but said that because of the design if the amp, an issue in one part of the amp is very hard to pin down because 'everything is coupled'. He said its not worth repairing because all he could do is start replacing bits at the start of the chain and move down until the issue is solved.

I'm no expert by any means and he sounds convincing BUT, I can't help but wonder if something can be done. I'm a PG Ti die hard tragic and I don't want to lose this amp.

So, seeking your help here guys and would welcome your comments on how to go about getting this amp right again.

Thanks, all the way from Australia.

trickyricky · Post by **trickyricky** » Fri Mar 08, 2013 4:59 pm

It's repairable and it's worth it. I'm currently working on mine but had to take a break because it was kicking my ass, lol.

Every channel is the same so he can a/b the bad channel to a working channel. Heck you got a 475 that's basically the same amp, take both to your tech so he can a/b them aside by side to see what may be the problem.

Gain pots seem to be a major problem with these amps....have you cleaned them out.

winno · Post by **winno** » Fri Mar 08, 2013 8:55 pm

I'm hoping that what you say is true.
The trouble is, the tech has made it clear that he's not keen on working on this amp (maybe he only wants easy work - I'm not sure) and I would rather have someone do the job that doesn't mind working on it.
I would take it back to him but only if someone else here had the same issue and knew what was done to fix it. To give this tech some key pointers, as it were.

I'll look into the gain pot issue but would still welcome any other input.

Cheers.

LowandLoud · Post by **LowandLoud** » Sat Mar 09, 2013 6:14 pm

Or.... you could send it to Valeks1 and for a set price, you would have it fixed by a guy who knows these inside out. The shipping might be a deal breaker though.

LL

winno · Post by **winno** » Sat Mar 09, 2013 9:14 pm

Yeah, shipping will be the killer there, especially as these amps can be purchased for about AU$450 or even less now locally.

MW3 · Post by **MW3** » Sun Mar 10, 2013 2:15 am

Its 90% likely it a bad config switch or potentiometer.

winno · Post by **winno** » Tue Mar 12, 2013 12:40 am

Ok, I'll pull the back off the pots and give them a good clean out with some contact cleaner.
I heard somewhere, some time ago from someone that this might have been an issue with another Ti amp of the same vintage.
Will report back in a few days.

Cross fingers...

MW3 · Post by **MW3** » Tue Mar 12, 2013 4:30 am

Just change the setting on the config switch see if the problem goes away, or wiggle the potentiometers one at a time.

I would not remove the switch or pots from the board, its very easy to damage traces unless you are used to repair work.

winno · Post by **winno** » Tue Mar 12, 2013 8:52 pm

I wouldn't remove them from the board.
I've tried dry wiping all the switches for about a minute each to no avail.

Will try a wet clean as soon as I get the chance.

trickyricky · Post by **trickyricky** » Wed Mar 13, 2013 4:56 am

DeoxIt works very nicely.

winno · Post by **winno** » Thu Mar 14, 2013 10:56 pm

Ok, the tech said that wet cleaning all the pots and switches was the first thing he did as he said they're a common issue on these amps.

The problem is still there.

Any other ideas?

Cheers everyone.