amplifier repair help

[jdeaton01 10+ year member]

this might not be the right spot to ask this question but i couldnt find the right place if this isnt it. i am currently trying to repair an xterminator xt1600.2 that was given to me and i need to know a few things. what do i need to set my ohm meter on when i check the transistors??20k 200k or 2000k? and what should the ohm meter read? i attached some photos. if anyone could tell me which are the input and output transistors and if the smaller transistors should read different than the larger ones it would be greatly appreciated!!!!!!

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[akheathen Premium Member]

ok, set your meter on the lowest ohm setting. what you are checking for is shorting, so it would read 0-ohms, or close, really anything under 2ohms across any 2 legs of any of them. in this amp there are 2 rectifier diodes. so here's the basic layout:

-the 8 large transistors with the large emmiter resistors attatched to them are the outputs. you are going to want to measure the resistance of the resistors, too. if one is bad, you have to replace all of them in that section (4) and their resistors, or the amp is gauranteed about 90% that it will not last, and need to be fixed again.

-the smaller ones make up the power supply that feed the output it's voltage, and they have small gate resistors. it may look like there is 4 of them on each side, but really, there is only 3 on each side in this amp, and the 4th on the left, aside from where the board is split, are the rectifier diodes, and they will read low resistance, and that is ok. they rarely fail, too.

- the way it works, is the little ic by the power terminals controlls the 6 power transistors and switches them so that there is a 12vac signal running through the round transformer, called a "torroid" then, there is the secondary windings that pick up that ac at a different voltage and feed it to those 2 rectifier diodes so that it turns back into dc to power the outputs. you actually picked a real nice simple design amp for learning how they work. if you find one on an array that reads a short across all 3 legs, you can clip that out, and re-check the others. same if you only find one, that has the lowest resistance, since it will be feeding continuity through the emitter resistors to the other ones. if, then, you still have at least one good one in each circuit, you can power it up to idle with a 5a fuse and no speaker/load attached to the outputs. check that you get ghood rail voltage, by measuring at the output legs, with the other probe on the speaker common terminal. you will have a (+) and a(-) voltage, and they should be pretty close to the same. measure the output on dc to make sure you do not have dc at the speaker terminals. if that all checks out. you can hook a 4+ohm speaker up and play at a low volume. this will tell you if there is any other damaged components, and any large amounts of power you try to push in this condition will likely lead to 2x the damage or more. good luck, and have patience. lmk if you need any soldering advise.

 

[jdeaton01 10+ year member]

so i need to set the meter to 2000k? or the bottom setting which is just 200? im really new to this but i catch on quick. when i set it to 2000k the small ones at the top of the amp read 002 and the bottom reads 001 and then the large ones on the left side of the amp read 165. does this mean the power transi are bad and need to be replaced?

 

[jdeaton01 10+ year member]

anybody?

 

[Timmothy Web 10+ year member]

how far are u from memphis?

 

[bubbagumper6 5,000+ posts]

so i need to set the meter to 2000k? or the bottom setting which is just 200? im really new to this but i catch on quick. when i set it to 2000k the small ones at the top of the amp read 002 and the bottom reads 001 and then the large ones on the left side of the amp read 165. does this mean the power transi are bad and need to be replaced?

Set it to the LOWEST setting. 2000k = 2000000 so that is not the lowest. All changing that setting really does is move your decimal point and change the range at which you're reading. Since you're trying to read very small resistance values you want to use the 200ohm setting.

 

[jdeaton01 10+ year member]

Set it to the LOWEST setting. 2000k = 2000000 so that is not the lowest. All changing that setting really does is move your decimal point and change the range at which you're reading. Since you're trying to read very small resistance values you want to use the 200ohm setting.

ok i put my meter on 200ohm. the only thing my meter says when i touch the two outer legs on all of them is 1blank blankthen a decimal. i figure that means there is no reading. so does this mean i need to get a diff multimeter?? its a cheap one lol. the only reason i i checked it on 2000k and 200k is because that was the only setting i was getting a reading on.

 

[akheathen Premium Member]

what does it read when you touch the leads together? how good is the battery?