They look different. UGH, now what? bad transistor?The mute relays are part of the power board.
Check the collectors of the upper and lower transistors that drive the STK module with the scope, on both channels?
If the signals there are identical on both channels, the fault can only really be in the STK module, something failed within its bias control presumably..
View attachment 138148
Q13 and 15 read a short across b and e, in circuit.So scope on q9, 11?? How? Sorry, I'm very new with this, and a scope. ThanksCan you post the Q09 & Q11 waveforms from both channels? Also, what is the voltage between those two points with the amp idle? (for each channel).
Q13 and Q15 are part of the protection circuit. They are used to sense the voltage across the power stage output resistors (R51 & R53) and limit the drive to the STK is the current is too high.
They should read 220 Ohms between emitter and base while in circuit and unpowered, due to the base-emitter resistors?
Check the R51 & R53 output resistors are reading under one ohm and inspect the solder joints, make sure there are no cracks or dry joints?
If those are OK, you could remove or lift one end of D07 and D09, to isolate the protection part from the STX input drive. Just keep the volume very low to avoid any possibility of overloading the amp whilst unprotected.
Then check the collectors of Q09 & Q11 again & see if the output distortion has gone when checking with the scope?
It's certainly not impossible both transistors have failed, though it seems a bit of a coincidence. If it's OK with those diodes disconnected I'd definitely replace Q13 &Q15, and reconnect the diodes.
[Use the part number equivalents in the faulty channel if I'm looking at the wrong one ?]
d07,d09 lifted, still have bad output on speaker out on that channel.Can you post the Q09 & Q11 waveforms from both channels? Also, what is the voltage between those two points with the amp idle? (for each channel).
Q13 and Q15 are part of the protection circuit. They are used to sense the voltage across the power stage output resistors (R51 & R53) and limit the drive to the STK is the current is too high.
They should read 220 Ohms between emitter and base while in circuit and unpowered, due to the base-emitter resistors?
Check the R51 & R53 output resistors are reading under one ohm and inspect the solder joints, make sure there are no cracks or dry joints?
If those are OK, you could remove or lift one end of D07 and D09, to isolate the protection part from the STX input drive. Just keep the volume very low to avoid any possibility of overloading the amp whilst unprotected.
Then check the collectors of Q09 & Q11 again & see if the output distortion has gone when checking with the scope?
It's certainly not impossible both transistors have failed, though it seems a bit of a coincidence. If it's OK with those diodes disconnected I'd definitely replace Q13 &Q15, and reconnect the diodes.
[Use the part number equivalents in the faulty channel if I'm looking at the wrong one ?]
q9, q11 still have an odd waveform compared to q10,q12 on clean channel, with the diodes lifted. Where is this signal going bad. GRRRRCan you post the Q09 & Q11 waveforms from both channels? Also, what is the voltage between those two points with the amp idle? (for each channel).
Q13 and Q15 are part of the protection circuit. They are used to sense the voltage across the power stage output resistors (R51 & R53) and limit the drive to the STK is the current is too high.
They should read 220 Ohms between emitter and base while in circuit and unpowered, due to the base-emitter resistors?
Check the R51 & R53 output resistors are reading under one ohm and inspect the solder joints, make sure there are no cracks or dry joints?
If those are OK, you could remove or lift one end of D07 and D09, to isolate the protection part from the STX input drive. Just keep the volume very low to avoid any possibility of overloading the amp whilst unprotected.
Then check the collectors of Q09 & Q11 again & see if the output distortion has gone when checking with the scope?
The two yellow junctions I marked on the diagram, earlier - you say you are seeing different waveform there between the two channels; can you post photos of the waveforms you see, for all four points?So scope on q9, 11?? How? Sorry, I'm very new with this, and a scope.
Thanks. Still trying to figure out this scope. It's an analog tek 2235. I have to change the v and ms when measuring anything besides the speaker output. It's definitely challenging for meThe two yellow junctions I marked on the diagram, earlier - you say you are seeing different waveform there between the two channels; can you post photos of the waveforms you see, for all four points?
Also please measure (DC voltage) between those two point, in each amp channel, with power on but no signal?
The two yellow junctions I marked on the diagram, earlier - you say you are seeing different waveform there between the two channels; can you post photos of the waveforms you see, for all four points?
Also please measure (DC voltage) between those two point, in each amp channel, with power on but no signal?
Whilst the D07 & D07 were out, Q13 & 15 could not cause a problem; leave the diodes out and forget them for now - the problem is to the left of those, in the circuit.Soldered everything back in.
Sorry. As I said, I'm lost. I forgot those other voltages. So voltage from d07 to d09???one leg on each? 2.15 volts across. And I don't understand to the left. the left on the schematic?? That ac setting helped big time with the scope. I just assumed to use dc. So i narrowed down the bad signal to R37. Its bad on one side, not clean. Thats where I get the ugly wave. I don't think that tells anything though. LOL.Whilst the D07 & D07 were out, Q13 & 15 could not cause a problem; leave the diodes out and forget them for now - the problem is to the left of those, in the circuit.
You have not given the voltage measured directly between the two yellow points for each channel; that is critical.
Leave the scope set for AC coupling and it should work on the same setting for speaker or the yellow points.
Post photos of the waveform on the yellow points, both channels?
You could also check that you have around 0.6-0.7V between base and emitter in all the transistors to the left of the STK in the circuit?
The diodes should still be disconnected, so between the junction of Q09 collector to the STK and Q11 collector to the STK.So voltage from d07 to d09???one leg on each? 2.15 volts across. And I don't understand to the left. the left on the schematic??
Yep, that sounds about right.So new stk, and replace q13,q15???
Extremely simply - it's very, very easy.Unit is alive again! Put 2 stk 0105's in. Sounds really nice. Anyone know how to measure wattage output with a scope? Here's a pic of it in action.
You need to consider how the amplifier (and pretty well all other transistor amps) works - the output power is essentially dependent on the supply rails - NOT on the output devices. If the output devices aren't capable - they will overheat and die.Thanks for the instructions. Only reason I wanted to test it, was see what the aftermarket 0105's put out. But I guess your right. What's the difference? It sounds great, and i will never be playing at full power.
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