TOA 900 series ii Amplifier P-912MK2

[Bterrier]

Re: TOA 900 series ii Amplifier P-912MK2

I have disconnected and removed the pcb a few times thus far, the most recent being after the fuse popped.

I did notice something upon removing the pcb this time. It appears that par of the trace is damaged. Appears to be the section connecting Pin 3 on cn106 to ry101.

At first I thought this may have occurred after the fuse issue, but looking back at a previous photo from earlier in the night, the issue was already there. Please see attached photos.

The photo with red circles is prior to the fuse/short issue. The other is after the fuse popped, but also after I touched it.

Could this be the sole issue? How can I repair this?

[R_J]

Re: TOA 900 series ii Amplifier P-912MK2

Where the bad trace is, just solder a small piece of wire between the plug connection and the relay contact then to the other spot I marked. Also resolder the connections on that relay, and any others that look bad.
Those traces were getting hot due to the current running through them, it may be that the traces where a bit under sized,

If the trace was actually open, then it could cause the fuse to blow as it is ground for part of the curcuit. Repair it and hopefully the amp is ok

[Bterrier]

Re: TOA 900 series ii Amplifier P-912MK2

I did mke the repair to the trace and now have continuity. I think that may have fixed the protect mode issue, but I cant be positive because the fuse keeps blowing. It is F101 250v 6amp.

It is strange because it didnt pop at all until last night. Any advice as to what may be happening?

How do I test the four main transistors? Q115, q116, q117, q118?

[R_J]

Re: TOA 900 series ii Amplifier P-912MK2

Check the transistors using diode test on your meter, with power off check for a short between collector and emitter, ther should not be low resistance, then check from base to emitter, then base to collector, depending on the probe polarity and the transistor you should read about .6xx one way and open or high resistance the other way.
make sure your repair is'nt causing a short.
I assume you have installed the board back in the unit, make sure you have the grey insulators between the output transistors and the heatsink.
The schematic seems to have mixed up pins 2 & 3 of CN106, although they are both ground, pin 3 is the ground that goes to the relay and then to other parts of the circuit.
Although those traces looked bad, slightly melted, were the actually open? or just looked bad.

[Bterrier]

Re: TOA 900 series ii Amplifier P-912MK2

Check the transistors using diode test on your meter, with power off check for a short between collector and emitter, ther should not be low resistance, then check from base to emitter, then base to collector, depending on the probe polarity and the transistor you should read about .6xx one way and open or high resistance the other way.
make sure your repair is'nt causing a short.
I assume you have installed the board back in the unit, make sure you have the grey insulators between the output transistors and the heatsink.
The schematic seems to have mixed up pins 2 & 3 of CN106, although they are both ground, pin 3 is the ground that goes to the relay and then to other parts of the circuit.
Although those traces looked bad, slightly melted, were the actually open? or just looked bad.

I just tested the transistors. Here are my results, maybe you can assist me with analysis.

Q114 - Collector to Emitter = 0V regardless of polarity
Base to Emitter = 0V " "
Base to Collector = 0V " "
Q115 - Collector to Emitter = 0V " "
Base to Emitter = 0.005 " "
Base to Collector = 0.005 " "
Q116 - Collector to Emitter = 0V " "
Base to Emitter = 0V " "
Base to Collector = 0V " "
Q117 - Collector to Emitter = 0.144V " "
Base to Emitter = 0.144 " "
Base to Collector = .005 " "

I also went back to test the emitter resistors again because the fuse initially popped when I was checking voltage on these.
R123=0-0.1
R124= 0-0.1

R125= 0.01
R126=239.4

I am thinking that the 2nd emitter resistor is bad? Or can something else cause this?

The traces are ugly. One of them was just ugly, but the other was open so I repaired that one. I only repaired the open part for now until I can get the board operating properly. The repair is not shorting anything.

I am going to reinstall the board now

[R_J]

Re: TOA 900 series ii Amplifier P-912MK2

How was your meter set when you checked the transistors, and did you have power on or off?
Does your meter have DIODE test? You need to check the transistors that way, with power OFF You are not measuring voltages!
in diode test if the junction is good it should read .6 or .7 one way and OL the other. It is like checking two diodes, base to collector is one, base to emmiter is another, then lastly check emmiter to collector, this should be OL or open.
R126 looks like it IS open, that usually indicates Q116 could be shorted.

[Bterrier]

Re: TOA 900 series ii Amplifier P-912MK2

How was your meter set when you checked the transistors, and did you have power on or off?
Does your meter have DIODE test? You need to check the transistors that way, with power OFF You are not measuring voltages!
in diode test if the junction is good it should read .6 or .7 one way and OL the other. It is like checking two diodes, base to collector is one, base to emmiter is another, then lastly check emmiter to collector, this should be OL or open.
R126 looks like it IS open, that usually indicates Q116 could be shorted.

Yes my meter was set to Diode mode, which is why I am confused. When I test the small transistors, I get results of around 0.5 and OL when reversed. I am not sure what to make of the results from Q114-Q117.

Do you know where I can find a replacement for R126? I checked mouser but cant seem to find what I need

[R_J]

Re: TOA 900 series ii Amplifier P-912MK2

On the transistors you mesured Q114-Q117 you only have the one reading, did you reverse the probes and do the check? If they are are not checking properly, unsolder the E & B from the board and check them,
It might be hard to find that exact type of emitter resistor, they make others or you can just replace them individually.

[Bterrier]

Re: TOA 900 series ii Amplifier P-912MK2

On the transistors you mesured Q114-Q117 you only have the one reading, did you reverse the probes and do the check? If they are are not checking properly, unsolder the E & B from the board and check them,
It might be hard to find that exact type of emitter resistor, they make others or you can just replace them individually.

Yes, I did reverse the probes. I got the same reading both ways. I will unsolder and test.

Thanks

[Bterrier]

Re: TOA 900 series ii Amplifier P-912MK2

I did remove Q116 from the board and I am still getting the same readings as before. Is there another way to test this transistor? Is this a different type of transistor?

I am going to replace the emitter resistor, but I also want to ensure the these large transistors aren't the root cause.

[Bterrier]

Re: TOA 900 series ii Amplifier P-912MK2

I also re-measured resistance across R126 with the tranistor Q116 removed and I am getting 1.96K

[R_J]

Re: TOA 900 series ii Amplifier P-912MK2

Check the reading with Q117, it should be the same (PNP) transistor. The readings you gave were:
Q116 - Collector to Emitter = 0V " "
Base to Emitter = 0V " "
Base to Collector = 0V " "
Q117 - Collector to Emitter = 0.144V " "
Base to Emitter = 0.144 " "
Base to Collector = .005 "
They don't look right at all, Q117 seems to be shorted according to your reading.
Is that with the black probe to the base and the red to the C & E ?
then did you reverse the probes and do the test again? ?
Q114 & Q115 (NPN) should give similar reading BUT with the probes reversed
Have a look at this video https://www.youtube.com/watch?v=IY5UEbNB_fo

[Bterrier]

Re: TOA 900 series ii Amplifier P-912MK2

Check the reading with Q117, it should be the same (PNP) transistor. The readings you gave were:
Q116 - Collector to Emitter = 0V " "
Base to Emitter = 0V " "
Base to Collector = 0V " "
Q117 - Collector to Emitter = 0.144V " "
Base to Emitter = 0.144 " "
Base to Collector = .005 "
They don't look right at all, Q117 seems to be shorted according to your reading.
Is that with the black probe to the base and the red to the C & E ?
then did you reverse the probes and do the test again? ?
Q114 & Q115 (NPN) should give similar reading BUT with the probes reversed
Have a look at this video https://www.youtube.com/watch?v=IY5UEbNB_fo

Apparently I was testing these transistors incorrectly. I removed Q117 and Q116 from the board. Q114 and Q115 are still installed. Here are my results:

Q114 (red probe to base)
Base to collector =0v
Base to emitter =0v
Probes reversed =0v

Q115 (red probe to base)
Base to collector =0.005v
Base to emitter =0.005v
Probes reversed =0.005v

Q116 (black probe to base)
Base to collector = 0v
Base to emitter =0v
Probes reversed =0v

Q117 (black probe to base'
Base to collector = 0.536v
Base to emitter = 0.538v
Probes reversed = OL


How do these transistors look now with these results? Retested R126 with q116 and q117 removed : still a reading of 1.96k

[R_J]

Re: TOA 900 series ii Amplifier P-912MK2

I might not understand the "0v" If you short the probes together on your meter is it the same "0v"?
It looks like the only only transistor that might have checked ok is Q117
With those output transistors disconnected, also check Q110,111,112 & 113, and R117, R121,R122, R127, R128, R130. They may have been damaged.
R126 is open, they usually open due to a shorted output transistor like Q116, If it shorts it applies the full 45 volts across that .22 ohm resistor, it will open almost instantly.
There should have been a high voltage measured of either + or - 45 volts on L101 but due to the open ground trace I suspect thats why it read 0 volts earlier.

[Bterrier]

Re: TOA 900 series ii Amplifier P-912MK2

I might not understand the "0v" If you short the probes together on your meter is it the same "0v"?
It looks like the only only transistor that might have checked ok is Q117
With those output transistors disconnected, also check Q110,111,112 & 113, and R117, R121,R122, R127, R128, R130. They may have been damaged.
R126 is open, they usually open due to a shorted output transistor like Q116, If it shorts it applies the full 45 volts across that .22 ohm resistor, it will open almost instantly.
There should have been a high voltage measured of either + or - 45 volts on L101 but due to the open ground trace I suspect thats why it read 0 volts earlier.

Yes I just checked on my meter and if I touch the probes together in diode mode, it reads 0V. Strange because it reads OL on q117.

With these readings, do q114, q115, and q116 need to be replaced? I will recheck all of the smaller transistors and resistors you mentioned.

As for R125/R126, I contacted TOA and they have discountinued that replacement part. If I cannot locate an exact replacement, can I simply utilize 2 axial 0.22 5w resistors?

Also is there anything that would cause the transistors (q114-q117) to short? I wouldnt want to have them short again once I replace them and power .

[R_J]

Re: TOA 900 series ii Amplifier P-912MK2

Now I'm confused. in post #33 you said :
Q117 (black probe to base’
Base to collector = 0.536v
Base to emitter = 0.538v
Probes reversed = OL
Now you say Q117 reads OL ?

Q114,115,116 are checking shorted, correct? If you measure across the transistor leads and it measures the same as if the probes are placed together, the transistor is shorted.
You would need to replace all 4 outout transistors. You can use 2 axial resistors but they do sell the ones I posted also which are ment for this.
I have no idea what caused the issue, where did the amp come from? It could have been the amp that self destructed or something that was connected to the output that should'nt have been connected.
I would use a variac to slowly increase the ac to the amp to test it aftre the parts are replaced, you can use a incandesent lamp (60-100w) in series with the ac line to limit the current and help prevent the amp from blowing up if there is a problem.

[Bterrier]

Re: TOA 900 series ii Amplifier P-912MK2

Now I'm confused. in post #33 you said QUOTE=Bterrier;823117]
Q117 (black probe to base'
Base to collector = 0.536v
Base to emitter = 0.538v
Probes reversed = OL

[/QUOTE]

I apologize if I have confused you. There has been a learning curve here for me. Prior to post #33, I was not accurately testing the transistors. The numbers in post 33 are accurate and current

[R_J]

Re: TOA 900 series ii Amplifier P-912MK2

So q117 checked ok, and could be good but I would not chance it. the other transistors should check this way also.
Q117 and Q116 are PNP so Black probe on base you should read .5xx when checking to c then E
Q115 and Q114 are NPN so RED probe on base you should read .5xx when checking c then E
Measuring between E and C should always be OL in diode test

Now because these transistors are shorted, they could have supplied the 45 volts back to the driver transistors, this may or may not have damaged them, they should at least be checked with the meter.

[Bterrier]

So q117 checked ok, and could be good but I would not chance it. the other transistors should check this way also.
Q117 and Q116 are PNP so Black probe on base you should read .5xx when checking to c then E
Q115 and Q114 are NPN so RED probe on base you should read .5xx when checking c then E
Measuring between E and C should always be OL in diode test

Now because these transistors are shorted, they could have supplied the 45 volts back to the driver transistors, this may or may not have damaged them, they should at least be checked with the meter.

Ok, so I took your advice and tested Q110, q111, q112, q113, r117, r121, r122, r127, r128, r130.

q113 tested good. q110, q111, and q112 are NG. All resistors tested good except I am unsure about R121 and R122. The schematic shows a value of 1k. I am getting a reading of 0.493K.

I will definitely replace q110-q117 as well as r125/r126. Unsure about r121 and r122.

[R_J]

Re: TOA 900 series ii Amplifier P-912MK2

R121 and R122 are basically in parrallel, one end is connected together and the other ends are connected via R123 and R124 so R121 or R122 will read one half or 500 ohms (0.493k)
R127 and 128 will each read 1K because R126 is open.