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Old 1st March 2004, 10:26 PM   #1
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Default Amplifier repair

Hello all,

I recently picked up a blown MTX 2300x strictly for a learning project as I have taken a recent interest in amplifier design. I am still quite new to this, so please bear with me...

The original owner was hooking up a capacitor when the amp blew.

I hooked up the amp on my bench with no input, and no speakers hooked up and read 44VDC across the left channel. It would read 44VDC for 2-3 seconds, drop to 0V for about 1 second, then continue repeating the cycle.

I took the amp apart and found one shorted fet on the left channel.

I removed the 4 fets in that group (center row, top) and tested the amp again (is this a bad idea?)

Now with the fets removed on the left channel I powered up the amp to see if there was any output on the right channel. It was very weak and severly distorted, could this be due to the fact the fets on the left channel are removed?

Also, the fan does not start for some reason, before I removed the fets the fan worked, but was super noisy. I am not sure if it is activatedy by a rise in temp. or not.

I am going to remove the rest of the fets tonight and test for shorts.

Are there any other tests I can perform on the amp before I solder in some new parts? I dont want to replace them all again. Anything else I can test while I have it apart?

Thanks for any help.Click the image to open in full size.
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Old 6th March 2004, 01:48 AM   #2
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Default Argh

I've been repairing MTX amplifiers since they came out (back when PPI was building them). I HIGHLY recommend sending any 2300 or 2300x in to MTX for repair. I spent a month rebuilding one only to have it go up in smoke the second I turned it on. It's much easier to pay MTX $100 plus shipping, and its well worth it.

The fan is shot. It is temp controlled, but always spins up a bit. There is more going on with the amp than just an improper connection. It sounds as though it was severly abused electrically.
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Old 6th March 2004, 02:15 AM   #3
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Just curious... when did PPI make MTX amps, specifically what series, during what years.....I had an old MTX amp that sounded great. Too good to be MTX to be honest..... I kinda wish I still had it

Thanks....

Nathan
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Old 6th March 2004, 05:37 PM   #4
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Default PPMTX amps

PPI made amplifiers for a number of companies during the late 80's/early 90's. Such as:

G&S Designs
MTX
Audio Art
PSL
Sedona (was PPI's lower end line sold to PSL)
and a few others

PPI always used a chassis-mounting design that used the bottom plate to hold the power transistors in place. Every amp PPI made used this technique, which was probably the best advancement in car audio reliability.

The old Blue Thunder and Terminator Series were PPIs regular and ProMos series, respectively. MTX started designing their own amps, the Thunder Series in 1994 with the introduction of the 2XXX/4XXX series. These did not have crossovers built in, were Pure N channel MosFet output and were very clean and reliable. These amps put MTX on the map, to be sure.

IIRC, The next year they reintroduced the Blue Thunder Amplifiers using the same chassis and design as the Thunder Amplifiers. In fact, there was no difference between the regular and the Blues except for a modified logo and paint color (a hideous grey/blue). That same year, they also had the Black Gold amplifier that had a very distinct appearance. MTX did not design/build this one, and there is still some debate about who made this one for them. It appears to be a mix between Phoenix Gold and PPI. Nevertheless, it was MTX's best amplifier line ever. It was virtually indestructible and had massive headroom. Unfortunately, the kids didn't buy enough and the model was discontinued the next year.

That's about all I've got in my head as far as the amps go.

P.S. Their Class D amplifiers have had serious problems since Day One with the D500. Buyer Beware.
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Old 6th March 2004, 05:43 PM   #5
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Yep it was a four channel Blue Thunder....my first amp actually. I'm pretty sure it was 75 x 4, though I had it bridged to two channels to run a pair of Cerwin Vega XL-12s(in the cab of a pickup truck)....teenage bliss......ahh those were the days

thanks for the info......

Nathan
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Old 6th March 2004, 06:13 PM   #6
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Thanks for the suggestion, but to be honest I picked this amp up as a learning project, so if I can't get it up and running again, no big deal.

I removed the fan and hooked it up to a power supply, and it works fine. I also had a look at a couple other 2300x's and they fans did not come on when the amp was turned on.

Im going to try and rebuild it once, and if it goes up in smoke I'll consider sending it in (if it doesn't explode on the bench ).
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Old 6th March 2004, 06:54 PM   #7
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On a side note, anyone know where to find Fairchild SSP45N20A Mosfets? I tried a google search and only found 20B's. Thanks.
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Old 7th March 2004, 04:44 AM   #8
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Default Obsolete

It's been replaced with the 20B. Can you just buy that?

AudioLabGA.com has 8 in stock of the 20A for $3.00USD each.

Otherwise it crosses to a high capacity IRFB42N20D (200V, 44A, 55mOhms at 35C) at Future.ca, but you have to buy 50 of them at $1.40USD each.
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Old 7th March 2004, 11:52 PM   #9
mray is offline mray  United States
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Hey guys...

Seems like there is some knowledge here on PPI amps....and I need some help. I bought two A600's recently off ebay (risky I know). These were replacements for an ADS 860MX. At any rate I am having some strange problems with them. First I am running both at normal two channel 4 ohm load to Infinity Ref's 4X6's and two eclipse 6-1/2" drivers. There is a large descrepancy in output between the two. The A600 running the two front 4X6's is very strong and the second A600 running any kind of speaker is roughly half the first.

Both have 13.5 voltage sometimes 14 at vehicle startup. In addition the strong A600 (powering the 2 4x6's) gets extremely hot and makes a low grade buzzing noise fom inside the amp. Both amps display the normal LEDS with no yellow leds on. The strong amp works great and sounds great but I am concerned about the heat and noise. The other A600 stays cool but just doesn't put out. I have swapped RCA's and speakers....no difference. I also am running an A1200 which is working fine. All amps have their own seperate short grounds and power supplies which are 8 guage.

Can someone help me out? Is my alternator the problem? How can I diagnose this problem? I do I repair it?
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Old 22nd March 2007, 12:24 AM   #10
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i know this is a super old thread but i just thought it was worth a bump..heh...i find it interesting learning about some of the history behind these things...

i still have 2 working Blue Thunder PRO 504 amplifiers in working condition...

i also have another 10 or so Blue Thunder PRO 504's on the shelf waiting for me to repair them.....
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