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Old 12th May 2013, 10:44 PM   #1
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Location: Washington State
Default PG Tantrum 1200.1

Hello everyone.

I received this amp for repair.

Powered up and had no output.

It had 2.578 vdc on the positive output terminals and 56.5 vdc on the negative output terminals.

I opened the amp and found 1 shorted output FET a (STW34NB20).

I found a source for them but they are very expensive.

Question: Not being familiar with PG amps is it safe to power up with the output Q108 removed?

Question: Is the small pot in the center of the board labeled R31 for setting bias?

The person who had this amp thought it was an extra gain and messed with the adjustments, I am not sure what its for or how to properly set the adjustment.

If it is for bias and the person cranked it, it could have caused the blown output.

I read in some other posts that the T-module goes out in these.

I am going to order a couple of output FETS and put them back in.

The gate resistor measures fine at 4.9 ohms and should be 4.7 but its still within tolerance I think.

Any help would be awesome.
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Old 13th May 2013, 04:56 AM   #2
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Question 1: yes you can power the amp up with defective outputs removed. But I suggest you replace all the outputs is any defective part of the bridge output section. This amp runs full H bridge design so the stereo chip is bridged internally and both output terminals are hot with respect to common ground of the power supply secondary, just out of phase with one another by 180 degrees.
4.7 ohms fusible resistors on the gates if they are out by more then tolerance color band spec then replace them. For what these cost I go new when possible and you can find them on ebay also. Seriously doubt if they clone fuse resistors, not enough money in it IMHO.
You can probably use a simple pull down resistors on the gate resistor to ground to protect the T chip, 10,000 ohms will likely suffice, and allow some realistic gate drive readings to be taken while outputs are out of circuit < this chip operates in very high bandwidth, its not like the offshore sub amps you see all the time, hence the reason for those thick Alumina insulators you will find under the outputs trying to decouple the metal tabs on the outputs from ground. As I said it operates on a much higher bandwidth then sub amps do. You need to think RF theory to reason why they did what they did, and this amp is built off the white papers from Tripath so a lot of what you see is all Tripath thinking.

The fact that one side has over 2 volts offset says they are either leaking badly or the gate driver in the T chip is damaged. And yes many sources I have found are over charging outrageously for T chip compatible MOSFET outputs. Tripath only certified one particular brand of outputs back then and whom ever has stock of them seems to know this and charges for this design compatibility issue, and the fact the manufacturer is no longer making them. I have seen prices as high as $38.00 for each output from some vendors. I just shake my head and move on to realistic vendors..Other outputs can be engineered into this amp, but its not a tech level job to do this. This amp is exactly from the white paper from Tripath.
If you dare alter to other outputs please pay attention to gate capacitance as this effects this driver IC's ability to operate at high bandwidth. For subs this might not be a issue but for full range 20 to 20 khz it is. Other issues like over heating of the outputs and T chip gate driver failure are also possible.

Question 2 : The small pot and the only adjustment inside of this amp as I recall and was told by PG engineers in the main power limiting set point, and yes there is a procedure and and it is in place to prevent the amp from being driven into unsafe operating areas. This adjustment needs to be set 14.4 volts DC power input to the amp and at 800 watts output at 4 ohms, or 1200 watts at 2 ohms.
These amps did not like 2 ohm loads due to the H bridge output stage seeing over current of the outputs SOA easily, And very often a 2 ohm load would leave the internals beyond repair causing the PC board to be burnt up in many cases, if over-fused or no fuse used.. Even PG engineers posted pics of burnt up 1200's that had been run at 2 ohm or less in many cases, and over or no fuse on the main power always destroyed the amp board beyond reuse.

I own a couple of these also, and I just picked up some chips off ebay from a vendor in Minn. for reasonable see link below:
TA0102A and TA0103A Tripath Module Stereo Class T Digital | eBay

So chips are available and for reasonable if you have time and patience in searching.
Need anymore help just ask away... hope this helps some...

Last edited by 1moreamp; 13th May 2013 at 04:59 AM.
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