Hi Ben
Q41 & Q43 are the output transistors of one channel, Q42 & Q44 belong to the other channel.
I'm puzzled why BOTH channels aren't working. It's unlikely that both pairs of output transistors blew at the same time.
I see you measured a voltage on both channels (Q44 & Q43). Have you replaced the blown fuse and it hasn't blown again?
Q41 & Q43 are the output transistors of one channel, Q42 & Q44 belong to the other channel.
I'm puzzled why BOTH channels aren't working. It's unlikely that both pairs of output transistors blew at the same time.
I see you measured a voltage on both channels (Q44 & Q43). Have you replaced the blown fuse and it hasn't blown again?
don't just replace the fuse and plug it back into the mains.
Replace the fuse, plug into your mians light bukb tester and then switch on the bulb tester.
If the amp is seriously overcurrent, the bulb will stay on and drop most of the voltage before feeding the transformer in the amp.
This way you get just a few volts out of the rectifier and generally nothing else gets damaged, not even the new fuse.
Start measuring some voltages to try to identify the damaged components.
Replace the fuse, plug into your mians light bukb tester and then switch on the bulb tester.
If the amp is seriously overcurrent, the bulb will stay on and drop most of the voltage before feeding the transformer in the amp.
This way you get just a few volts out of the rectifier and generally nothing else gets damaged, not even the new fuse.
Start measuring some voltages to try to identify the damaged components.
Yes, I'm not recommending you replace the fuse & plug it into the mains Ben. But if you've measured voltages on both sides I guess you already have?
Cyrus 2 no output
Thanks for the feedback gents, much appreciated.
First thing I did when no power was coming out, check the fuses. Only one blew. Both output terminals are dead. Why not just one side?? So, I proceeded with changing both fuses with spares but to no avail. Still do not have any power coming out at the terminals. I can't see any other "physical" damage anywhere. This is when I measured the voltage on all four OT and only getting a reading on Q43 and Q44.
Something else must of went... not sure what.
Ben
Thanks for the feedback gents, much appreciated.
First thing I did when no power was coming out, check the fuses. Only one blew. Both output terminals are dead. Why not just one side?? So, I proceeded with changing both fuses with spares but to no avail. Still do not have any power coming out at the terminals. I can't see any other "physical" damage anywhere. This is when I measured the voltage on all four OT and only getting a reading on Q43 and Q44.
Something else must of went... not sure what.
Ben
Cyrus 2 no output
If you guys suggest to inspect or get a reading from certain locations, could you indicate the IC address designation? (ie: Rxx, Qxx, Cxx)
Thanks again!
Ben
If you guys suggest to inspect or get a reading from certain locations, could you indicate the IC address designation? (ie: Rxx, Qxx, Cxx)
Thanks again!
Ben
Ok.
First thing I'd do is to disconnect from mains and remove both fuses.
Then, without removing them from the PCB, measure the resistance between the legs of each output transistor (Q41-Q44). E.g. Measure between leg 1 and 2, then between 2 and 3, then between 1 and 3.
If you get anything near zero Ohms then that transistor is probably short circuit (though it could be another component), so remove the transistor and repeat the check.
If Q41-Q44 appear Ok, do the same test on the smaller transistors between the output transistors (don't know their numbers - the ones with the small heatsink).
If they're Ok, do the same check for Q30 to Q34 (I think)
Let me know what happens...
First thing I'd do is to disconnect from mains and remove both fuses.
Then, without removing them from the PCB, measure the resistance between the legs of each output transistor (Q41-Q44). E.g. Measure between leg 1 and 2, then between 2 and 3, then between 1 and 3.
If you get anything near zero Ohms then that transistor is probably short circuit (though it could be another component), so remove the transistor and repeat the check.
If Q41-Q44 appear Ok, do the same test on the smaller transistors between the output transistors (don't know their numbers - the ones with the small heatsink).
If they're Ok, do the same check for Q30 to Q34 (I think)
Let me know what happens...
I removed the fuses and not sure what you meant by disconnecting the mains. But if it means to disconnect the power and speakers for the Cyrus, it's done (can't see anything else to disconnect). Then proceeded to measure the resistance of all 3 combination of the OT pegs (between 1 & 2, 2 & 3 and 1 & 3) and my readings are:
Q41 = 0, 0, 75 ohms
Q42 = 0, 0, 75
Q43 = 0, 0, 75
Q44 = 0, 0, 75
Don't think that's right though since I get this resistance from the PCB. So, I went ahead and removed all 4 OT. Same probing but still no reading from any of the 3 combinations - all 4 OT. Not good so far.
Probed Q39 and Q40 ...no reading.
I also probed Q31 to Q34 as instructed and got one reading of 160 ohms between 1 & 3 for all 4. Probing from 1 & 2 and 2 & 3 yielded no reading.
Any ideas or verdicts at this point?
Thanks!
Ben
Q41 = 0, 0, 75 ohms
Q42 = 0, 0, 75
Q43 = 0, 0, 75
Q44 = 0, 0, 75
Don't think that's right though since I get this resistance from the PCB. So, I went ahead and removed all 4 OT. Same probing but still no reading from any of the 3 combinations - all 4 OT. Not good so far.
Probed Q39 and Q40 ...no reading.
I also probed Q31 to Q34 as instructed and got one reading of 160 ohms between 1 & 3 for all 4. Probing from 1 & 2 and 2 & 3 yielded no reading.
Any ideas or verdicts at this point?
Thanks!
Ben
Ok
Firstly, keep the power & speakers disconnected & the fuses out.
When you say "No reading" when you measured them after they'd been removed from the PCB, do you mean that you get (between pins 1 and 2 say) zero Ohms (short circuit), or infinite resistance (Open circuit)?
Firstly, keep the power & speakers disconnected & the fuses out.
When you say "No reading" when you measured them after they'd been removed from the PCB, do you mean that you get (between pins 1 and 2 say) zero Ohms (short circuit), or infinite resistance (Open circuit)?
When I wrote no reading, meant that my meter doesn't register anything. Either infinite R or simply too low for my meter to read... Open circuit then?
If you touch the probes together, your meter should read zero Ohms (because there's zero resistance). That's a short circuit.
If you hold your probes in the air, not touching, that's open circuit.
So I guess the reading between pins 1-2 & 2-3 is Open Circuit?
If you hold your probes in the air, not touching, that's open circuit.
So I guess the reading between pins 1-2 & 2-3 is Open Circuit?
JoolsB indicated:
"(between pins 1 and 2 say) zero Ohms (short circuit), or infinite resistance (Open circuit)"
When I probe pegs 1 to 2, my meter doesn't give me a zero or any reading other than "1" which is the base "open" start point.
So frankly I am unsure if this means that it's either short circuit or open 😕
"(between pins 1 and 2 say) zero Ohms (short circuit), or infinite resistance (Open circuit)"
When I probe pegs 1 to 2, my meter doesn't give me a zero or any reading other than "1" which is the base "open" start point.
So frankly I am unsure if this means that it's either short circuit or open 😕
What reading does your meter show when set to ohms/resistance and the two test probes shorted together?benlalonde said:
What reading does your meter show when set to ohms/resistance and the two test probes are both in free air, i.e. touching nothing?
How many ohms/resistance scales does your meter have?
What are they? Full scale and resolution?
Andrew,
I get a zero reading (00.0) when test probes are together. Apart I get that "1".
The meter R scaling is 0-200-2k-20k-200k-2M±1.2% 20M ohm±3.0%
And if this has any helping value:
I also tried a continuity test for the hell of it. No continuity between any of the 3 pegs. However I do get continuity when probing middle peg (#2) and the copper heat transfer backing of the OT.
I get a zero reading (00.0) when test probes are together. Apart I get that "1".
The meter R scaling is 0-200-2k-20k-200k-2M±1.2% 20M ohm±3.0%
And if this has any helping value:
I also tried a continuity test for the hell of it. No continuity between any of the 3 pegs. However I do get continuity when probing middle peg (#2) and the copper heat transfer backing of the OT.
1 = open circuit.
0.0 on the 200ohms scale is impossible. There is lead resistance and tip to tip resistance. It usually amounts to 0r1 in a good set of leads/DMM to 0r4 in a bad set of leads/DMM.
effectively, 0r1 = short circuit.
0.0 on the 200ohms scale is impossible. There is lead resistance and tip to tip resistance. It usually amounts to 0r1 in a good set of leads/DMM to 0r4 in a bad set of leads/DMM.
effectively, 0r1 = short circuit.
Ok, that's open circuit and good news.
Going back to your original posts, you said that you measured these voltages after replacing the fuse:-
Q42 = 0 V
Q44 = 33.3 V
Q41 = 0 V
Q43 = 33.3 V
***I'm assuming from this that the fuse hasn't blown again and nothing is smoking***, so what I'd do is to replace the OT's, replace the fuses, plug into the power supply and read the DC voltages at all of the pins on all 4 OT's. Just to make sure we're talking the same language, your OT's do look like this don't they? (but with different markings). http://www.datasheetcatalog.org/datasheet/WINGS/TIP41.pdf
Number the pins from left to right (1=left, 3=right), looking at the OT from the front.
I think you should get something like this: -
Q41, Pin 1, 0v
Q41, Pin 2, +33v
Q41, Pin 3, 0v
Q43, Pin 1, 0v
Q43, Pin 2, 0v
Q43, Pin 3, -33v
Q42, Pin 1, 0v
Q42, Pin 2, +33v
Q42, Pin 3, 0v
Q44, Pin 1, 0v
Q44, Pin 2, 0v
Q44, Pin 3, -33v
Going back to your original posts, you said that you measured these voltages after replacing the fuse:-
Q42 = 0 V
Q44 = 33.3 V
Q41 = 0 V
Q43 = 33.3 V
***I'm assuming from this that the fuse hasn't blown again and nothing is smoking***, so what I'd do is to replace the OT's, replace the fuses, plug into the power supply and read the DC voltages at all of the pins on all 4 OT's. Just to make sure we're talking the same language, your OT's do look like this don't they? (but with different markings). http://www.datasheetcatalog.org/datasheet/WINGS/TIP41.pdf
Number the pins from left to right (1=left, 3=right), looking at the OT from the front.
I think you should get something like this: -
Q41, Pin 1, 0v
Q41, Pin 2, +33v
Q41, Pin 3, 0v
Q43, Pin 1, 0v
Q43, Pin 2, 0v
Q43, Pin 3, -33v
Q42, Pin 1, 0v
Q42, Pin 2, +33v
Q42, Pin 3, 0v
Q44, Pin 1, 0v
Q44, Pin 2, 0v
Q44, Pin 3, -33v
Ok, thanks! I will order 4 new OT. Do you have a good North American supplier to recommend? ..would be faster for me.
Should I stick with the PT77 or are there better ones from your experience??
You know, after all this, I'm not convinced that all 4 OTs have shorted. My reasoning on this is I only plugged in one speaker (with crossed leads). Should only "one" channel short out?!? Why all😕
Ben
Should I stick with the PT77 or are there better ones from your experience??
You know, after all this, I'm not convinced that all 4 OTs have shorted. My reasoning on this is I only plugged in one speaker (with crossed leads). Should only "one" channel short out?!? Why all😕
Ben
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