mtx thunder 2 channel

[allaroundsound]

working on an MTX thunder 8302. build date is 5/11/01. amp had shorted (x2)ssp45n20a. I pulled them and now the amp turns on. rail voltage is +/_ 32volts. It shows 15volts dc voltage on outputs. I have fired the amp up with a inline current limiter and measured some dc voltage at emmiter resistors for some of the remaining outputs. the lowest is .ooo5volts and the highest is .0006volts. Also all of the power supply filter and storage caps are ready to pop. Sorry for two much info in one post.

IC#494
Pin 1: 2.35
Pin 2: 2.35
Pin 3: 3.41
Pin 4: .844
Pin 5: 1.55
Pin 6: 3.44
Pin 7: .004
Pin 8: 12.76
Pin 9: .004
Pin 10: .004
Pin 11: 12.76
Pin 12: 12.81
Pin 13: 5.026
Pin 14: 5.026
Pin 15: 5.026
Pin 16:.004

 

[allaroundsound]

i will send a pic of the board in the morning.

 

[Perry Babin]

Which two of the outputs (circuit board designations) are out of the circuit?

Do you have any significant DC voltage across either pair of speaker terminals?

 

[allaroundsound]

check on that tomarrow. Work was swamped today. thanks

 

[allaroundsound]

removed fet 315 and 316. With fluke negative at main ground i have 7volt dc on right negative output and -7volts on left positive output. with fluke neg. @ rca shield i measure almost 30volts for the right channel and 18 volts for left.

 

[allaroundsound]

suitable replacement for ssp45n20a? both channels use 4 each.

 

[allaroundsound]

found a burnt component right next to the main storage caps. circuit board designation d92. top of says 817b, i think can't make out the bottom. Diode i presume?

 

[allaroundsound]

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[Perry Babin]

Does D 92 have one end connected to the main ground and the other end connected to the shield ground?

If it's shorted, you'll have to remove it to check for the connections to the grounds.

The IRF3415 should be a good sub for the SSP FETs.

 

[allaroundsound]

im not with the amplifier right now to answer that. I can say that d92 needs replacement. Do you know if it is a zener diode?

 

[Perry Babin]

It's likely an ES2D.

 

[allaroundsound]

yes like you said, d92 shows connected to main ground on one side. And the other rca shield.

 

[allaroundsound]

d92 looks to be smaller than the other ES2D labeled components around the power supply (d605,d601,d606). Is it possible that it may be something else, or shrunk in size when burnt up...? Do you have a schematic?

 

[allaroundsound]

i called mtx and the guy that answered the phone would not release the schmatic, but verified that d92 is a 4.7volt smd zener diode. He called it model mda011. I have d92 removed and still have considerable voltage on outputs right- and left+
With a jumper from main ground to rca shielding the voltage at the outputs increases by 10volts.
Any help would be appreciated guys.

 

[allaroundsound]

I noticed that i have -20.00 volts plus on all op amps on almost every pin in the preamp stage. Thanks for reading. I'll also note that the dc on the outputs changes alot when ajusting the independent left and right gain knobs.

 

[allaroundsound]

i have yet to receive replacement parts for the outputs and the smd zener @ location d92. I was hoping that there was something i could look at in the meantime. I know that this is not a stellar amp to be repairing, but it good for my experience. Thanks for any input.

 

[Perry Babin]

I'd suggest solving one problem at a time.

 

[allaroundsound]

i know and agree. just killin time on a sunday...