PPI PC1400 Help please
Ok, pulled this apart after letting it sit too long. I can see that q1 - q6 IRFZ-44N are shot and the seperation on the ground.
Well to start with your gonna need to remove all the blown fets on the burnt side and start cleaning everything up with some solvent< I like to use acetone, and for speed and time sake you can just clip the leads on all the burnt fets for now to get them out of the way, and to ease removal one lead at a time. >.
Once everything is cleaned up and all the soot is removed you can see clearly what else is burnt like gate resistors, and gate drivers etc..It is very unusual that only one side of the fets burnt the way they did. Please clean and inspect the mica insulator underneath those burnt fets and see if it has any burrs of metal shorting thru the mica. Seen that a bunch if times also.
With only one side of the supply burnt I am also worried your power transformer or common mode noise filter may be shorted.
The burnt ground connection is also unusual also as it also points to a short to the case ground somewhere on the amp. We will need to find that issue and correct it along with burnt devices.
Also have you read Perry Babin's tutorial if so then your ready to meter the outputs and diodes to see if any of them have failed also. If not then please click the links below any of his thread posts to get to his training site. His site will guide you on all the most important things you will need to know. I borrowed them and added them below...
Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links
Ok fets removed and everything cleaned up
Well to start with please repair the burnt ground trace on the bottom of the board. This is a symptom of a problem so its probably OK to repair it first and get it out of the way. A simple jumper made of solder wick will do, but do not use too big of a conductor as this trace was meant to open like a fuse and not burn the board up.
With a amp like yours where the fets have failed, I usually start looking for why they failed the way they did. I suggest that you inspect the mica insulator underneath those burnt fets to see if there are any holes or debris compressed thru the insulators causing the short that has occurred. I have seen mica do this over the years and although its a natural material found as a stone based product it can be cut and damaged so it can allow a short to occur to the sink. I have seen this on Audison, PPI, and others that use this product. Usually it was metal fragments from the screw holes that hold on the bottom of the case.
Also I use a 1 inch paint brush dipped in acetone and a stiff animal hair bristle brush to clean up some more of that soot that is still on the board and components. It is conductive and can cause issues so its best to keep cleaning as best as possible.
Also if you have a DMM or DVM please ohm out all the gate resistors and the current limits on the gate driver transistors, I am fairly sure the gate driver transistors did not survive this failure. The gate drivers are those two little to-92 transistors near the power toroid. They often fail and are cheap to replace. MPSA-56 and MPSA-06 are their device numbers.
Let me know what you find on the resistors and drivers and what not....
ok, the gate resistors read as follows
now i'm not to sure how to test the gate driver transistors?
All the gate resistors should read the same...Could you ohm-meter the fets on the other side across any two leads and see if any are shorted?
The gate drivers are so cheap and plentiful I just replace them as a matter of common practice. They cost me 3 cents each to buy in bulk. So just for good practice replace them, they rarely survive a failure like this, better safe then sorry, plus a ohm meter will not tell you if they are leaky anyway, and I don't know weather your in reach of a scope to check the drives with. So be safe, and just replace them regardless.
All the gate resistors you measured should read the same in circuit The 10 & 17 ohm readings are questionable. that is why I want you to meter the undamaged fets. They possibly have failed also. If so then I would replace a couple of the fets < one on each side >and verify all the gate resistors and then replace the drivers. This should bring your power supply back to life. two fets one on each side is enough to power up your amp with for simple testing as to basic idle and such.
While your at it please meter your outputs and drivers in the audio sections. I don't want to overlook the possibility that a failure in that area has caused all of this. the outputs are the TIP-35 and TIp-36 devices, and there drivers are the smaller transistors in between the TIP's.
We are still looking for a reason why this happened, so the two fets back in the supply is enough to power up the amp for basic idle nothing more. but to do that we need to check all the other things first and clamp the amp board back into its sink for initial power up testing.
Let me know what you find....:)
how do I check the TIP-35, 36? after replacing the fets on each side I started to get 47 ohm readings on the gate resistors on 226 and 227 but after that they start getting all screwy again 22, 18, 19 and 231 won't read...
If any do not read 47 then they either elevated in value, or brunt open. Either way they need to be replaced. I would replace them all so they are all new but that is a option to most people. I just like to know they are fresh and in tolerance spec.
On the outputs just measure any two leads as a pair on each transistor. I like to read 1 to 2, 2 to 3.
If any are shorted they will read as such, You can compare A channel to B channel, TIP-35 channel A to TIP-35 channel B. It is doubtful both channels are damaged, so the bad channel will show up as 10 ohms or less across the leads, when the matching device across the board will read like diode junctions.
If any of this is getting too out of hand for you please go to Perry Babin's links for his training site. He has it all explained there with pictures also.
I'm trying to keep up but i'm obviously no pro. All of the tip 35, 36's read out 17 ohms. I have read over perry's site time and time again but i keep confusing myself. will the transistors act the same as if they were out of the board? I printed out his test form and have been using that when I go through them(on the board). Just any help is good help and I greatly appreciate your help!!!
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