Is it easy to fix a ti 500.4 after reversing the polarity???

vitocorlioni88 · Post by **vitocorlioni88** » Mon Jul 16, 2007 3:34 pm

When in stalling my amp i was very very stupid and had the positive and negetive 12 volts backwards. I had some poping and lots of smoke. PG said that it is repairable but it will be $125. I work at with people who can solder circut boards and am curious if the fix is difficult. I dissasembled the amp and notice everything looked fine, ie: no burnt out resitors and such. But the large capacitors by the power connectors had poped and were leaking something. Any help on this matter would be very helpful.

1moreamp · Post by **1moreamp** » Mon Jul 16, 2007 3:40 pm

You won't see burnt fuse type resistors they just go open circuit and that what is on every gate for every fet in the power supply. Usually popping and snapping sounds means burnt boards and components galore, and vented power supply capacitors , they should be leaking nicely now with the RP condition that happened to them. They like to explode so your lucky they did nor burst from the stress of RP.

If your lucky you will just need Power fets, and gate resistors <Fuse type>, and some caps and possibly some other little devices. I stock spare power supply control boards, just in case it went to its limits

vin78 · Post by **vin78** » Mon Jul 16, 2007 3:49 pm

I'm pretty surprised that it didn't protect itself.

It must of had a hard life

eyesofra · Post by **eyesofra** » Mon Jul 16, 2007 10:53 pm

a little confused here guys...isnt that the reason there's fuses there in the amp, to protect it . Why didnt they work then ?

1moreamp · Post by **1moreamp** » Mon Jul 16, 2007 11:54 pm

The internal fuse is for amp protection, but not for idiot protection

.

By the time a internal 30 to 40 amp fuse melts the caps would be well fried and burst open. No Amp was ever built to survive being abused, and hooking up the power wires backwards is considered abuse.

RP causes the caps to 1: overheat internally, 2: expand and literally boil the electrolyte chemical within, and 3: the casings are meant to vent, but sometimes they hold out till they literally explode, throwing aluminum shrapnel like a hand grenade.

All of the above is just the caps. The FETS have Free wheel diodes built into them to absorb back EMF off the power toroid to protect the FETs from back surging power stress. On RP these diodes now conduct forwardly as now there polarity is correct for a circuit to be made with the power hooked up backwards.
This overheats the FET dies in the package and causes them to melt internally. This now intern places 12 volts on the gates of the FET and this feeds back thru the fuse type gate resistors causing them to blow one by one till they are all open.
By this time the high current copper traces are red hot and are lifting away from the fiberglass board material < these traces were hot press glued to the board in the first place so they naturally release under this sort of heat loading>. Copper is laminated to fiberglass to make the circuit board in the first place. Only space craft use better materials like Kapton and aluminum or gold on ceramic to withstand this sort of environmental hazards.

Then all the IC's in the control circuitry are now absorbing a full RP, along with some of the diodes and transistors used to make the circuitry work properly. Some of these devices are now in full melt down from being RP'ed and instead of blocking voltages they conduct them and melt internally.

And none of this is big enough to blow a 30 to 40 amp fuse. The fuse was meant to fail 1: if you exceed the natural power limit of the amp. 2: You run too low of a load and exceed the rated power of the amp. And 3: to prevent the back of you car from becoming a BBQ pit.

Yes, its gruesome, but its true. I have even seen the power toroids melt the windings on the core and fuse them together just as if it had been welded that way.

I hope this helps to explain what I have seen so many times over the last 25 years or so. I have no idea how many times exactly I have seen this exact same issue. But I do know how to repair it. Its called rebuilt the entire power supply.

Now imagine for a moment that your a amplifier engineer looking down at this sort of mess and you glance over to the power terminals with those big, bright, bold, markings + and - big enough to poke your eye out, And you just stand there shaking your head, saying my God, Why?????

It pays to slow down when your doing the critical parts of a install, and connecting power to anything is one of those critical moments that it pays to be careful, slow down, and double check yourself. Be good to yourself and your equipment, Slow Down, take a deep breath, count to ten and then re-check everything twice before ever connecting power to any circuit.

On big power this mistake will kill you and anyone near you in a fire ball explosion that makes the sun look dim. On big power you only live long enough to make this mistake once. Then it doesn't happen anymore, funny how that works like that

eyesofra · Post by **eyesofra** » Tue Jul 17, 2007 4:41 am

thanx cecil....this is scary...

vitocorlioni88 · Post by **vitocorlioni88** » Tue Jul 17, 2007 10:24 am

So im guessing its not an easy fix :-p , but thx for all the info. I still do not know how i did not catch it before i connected the positive to the battery, but my excuse was it was a hot and long day, haha. Also i notice afterwards that the way the speaker wires hook up are reversed from the main power terminals. Thats probably why i did what i did, considering i connected all the speaker wires first. Well i guess i ll be sending it into PG and see what they can do.

Thanks agian!

1moreamp · Post by **1moreamp** » Tue Jul 17, 2007 12:25 pm

vitocorlioni88, its a fairly easy repair if you have done it a dozen times of so, then you can do it in your sleep. But if your just learning about electronics its a step by step walk through to get you safely complete in this job.

As of this moment you have no idea what toast and whats just half baked, so its a big job to a newbie. I am walking a fella through his Outlaw as i write this and he has electronics experience and i have to direct his every step this first time in his amp.
next time though he will ready to handle it on his own. I have several Ti power control cards thus it simplifies my work on these having stock of known good parts to just pop in and move on. PG will do the same, so it will be a snap for them or i to bring your amp back. But we are both professionals at this sort of this so we do it all the time, piece of cake!

Are you shipping from Italy to the US for repairs ? If so Neither PG or even my costs are your troubles. It will be customs and the friggin carriers with their fees and such.

I wish you luck and welcome aboard the forum

If you need more info don't hesitate to PM me. I try to help all that want it

vitocorlioni88 · Post by **vitocorlioni88** » Tue Jul 17, 2007 6:53 pm

Im shipping from so-cal, but with a name such as vito i need to put the Italian flag up

How much would you charge for a job like this?

1moreamp · Post by **1moreamp** » Tue Jul 17, 2007 7:25 pm

vitocorlioni88 wrote:Im shipping from so-cal, but with a name such as vito i need to put the Italian flag up How much would you charge for a job like this?

Probably not much different then PG. There prices are fairly low for keeping customer loyalty.

If you have any severe board damage they might deem it as replacement if so there flat rate might go out the window.

I wish I could be more promising, but without seeing the damage first hand I am guessing about the extent of the repair. I have seen the entire board burned up under the sinks in the power supply section before. It was so bad all the copper traces had de-laminated but there was no real way to reasonable repair this unit. C

vitocorlioni88 · Post by **vitocorlioni88** » Tue Jul 17, 2007 9:55 pm

Thats kool, i totally understand. Ill probably send it in to PG with in the week. Thx again for all your help.