For completeness it would make sense just to add the measured values you see in the output stage Q103, 104 and 105.
Ok, initially confused, but these ones are labelled differently. They are E/C/ and then a solid square.
Anyway, in that order, as before, bulb in main circuit, black clamped to case, red to component, 20V setting....
Q103 = 1.66, -0.00, 1.65
Q104 = 1.64, 1.65, 2.42
Q105 = 0.02, -1 .0, 2.4
That middle reading on Q105 I think is infinite. There is a space between the -1 and the .
Also, on one occasion whilst reading this leg I saw a little smoke rise from Q105 and the amp went into standby but then came back on. ??
Cheers.
And for good measure I did Q112. Same set up...
Q112 = -1 .0, -0.00, -1 .0 (again space between 1 and .)
?
Anyway, in that order, as before, bulb in main circuit, black clamped to case, red to component, 20V setting....
Q103 = 1.66, -0.00, 1.65
Q104 = 1.64, 1.65, 2.42
Q105 = 0.02, -1 .0, 2.4
That middle reading on Q105 I think is infinite. There is a space between the -1 and the .
Also, on one occasion whilst reading this leg I saw a little smoke rise from Q105 and the amp went into standby but then came back on. ??
Cheers.
And for good measure I did Q112. Same set up...
Q112 = -1 .0, -0.00, -1 .0 (again space between 1 and .)
?
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OK, we have something very amiss here. Many of those voltages are very low which suggests there could be a problem with those 470 and 220 ohm resistors.
The 'FU' 😉 designation means 'fusible'. These are resistors designed to fail open circuit without creating smoke (smoke scares the punters even though it would be harmless).
It sounds like you might accidentally have shorted the pins while measuring... it happens 🙂
R113 and R114 need checking along with R109, R110, R111, R112 and R107.
Smoke from a small transistor isn't good... it will be dead.
You also need to check that zener diodes D103 and D104 have not failed short circuit. Those can quickly be checked in circuit and if faulty can be snipped out temporarily.
The 2SC and 2SA type devices have a different pin out to the BC type with the collector being in the middle.
The 'FU' 😉 designation means 'fusible'. These are resistors designed to fail open circuit without creating smoke (smoke scares the punters even though it would be harmless).
It sounds like you might accidentally have shorted the pins while measuring... it happens 🙂
R113 and R114 need checking along with R109, R110, R111, R112 and R107.
Smoke from a small transistor isn't good... it will be dead.
You also need to check that zener diodes D103 and D104 have not failed short circuit. Those can quickly be checked in circuit and if faulty can be snipped out temporarily.
The 2SC and 2SA type devices have a different pin out to the BC type with the collector being in the middle.
Tested the good side.......
Q12 = -1_.0, 3.66, -1_.0
Q3 = 1_.0, 3.67, 1_.0
Q4 = 1.65, 1_.0, 2.21
Q5 = -1.96, -12.42, -1.96
Q12 = -1_.0, 3.66, -1_.0
Q3 = 1_.0, 3.67, 1_.0
Q4 = 1.65, 1_.0, 2.21
Q5 = -1.96, -12.42, -1.96
Yes, there may have been contact between e and c.....ooops
So I may have fried it?
So I may have fried it?
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Something has gone amiss. Its as if the supplies have gone down.
Make sure that you have the plus 44 and minus 44 volts present. Look at the circuit and the resistors and it will be clear.
One end of R114 and R113 should have 44 volts and one end of R107 should have -44. The 44 volts is derived from D102. In other words D102 should have 44 volts on each end.
I'll have to leave it for tonight but those readings suggest that the supplies have all but disappeared if the good channel is showing similar voltages.
Has a fuse popped ?
Make sure that you have the plus 44 and minus 44 volts present. Look at the circuit and the resistors and it will be clear.
One end of R114 and R113 should have 44 volts and one end of R107 should have -44. The 44 volts is derived from D102. In other words D102 should have 44 volts on each end.
I'll have to leave it for tonight but those readings suggest that the supplies have all but disappeared if the good channel is showing similar voltages.
Has a fuse popped ?
Hmmm... I think so.
I've been there a few times, and its all part of the learning process.
Fuse is fine.
I had the bulb in place but it didn't come on. Sounds exact same through headphones as before.
I am doing all these tests with a live input (zero volume) on the power amp input, is that necessary?
Resistor tests to chassis ground again? Better set to 200v this time.
Diode test across component whilst power on?
Cheers
I had the bulb in place but it didn't come on. Sounds exact same through headphones as before.
I am doing all these tests with a live input (zero volume) on the power amp input, is that necessary?
Resistor tests to chassis ground again? Better set to 200v this time.
Diode test across component whilst power on?
Cheers
Fuse is fine.
I had the bulb in place but it didn't come on. Sounds exact same through headphones as before.
I am doing all these tests with a live input (zero volume) on the power amp input, is that necessary?
Resistor tests to chassis ground again? Better set to 200v this time.
Diode test across component whilst power on?
Cheers
I had the bulb in place but it didn't come on. Sounds exact same through headphones as before.
I am doing all these tests with a live input (zero volume) on the power amp input, is that necessary?
Resistor tests to chassis ground again? Better set to 200v this time.
Diode test across component whilst power on?
Cheers
You don't need any input to the amp.
Voltages as before with black lead to chassis. Check those 44 volt lines first. The diode should have +44 on each end.
The resistor checks are with the amp OFF and using the meter to read across them on ohms range. If they read correct in circuit then that is fine. If they don't then you have to isolate one end as we did with the 1k before.
Voltages as before with black lead to chassis. Check those 44 volt lines first. The diode should have +44 on each end.
The resistor checks are with the amp OFF and using the meter to read across them on ohms range. If they read correct in circuit then that is fine. If they don't then you have to isolate one end as we did with the 1k before.
Ok. It's reading 0.00 and 1.62!!
By comparison D2 is 45.5 and 44.9
Latter readings from silver band side
By comparison D2 is 45.5 and 44.9
Latter readings from silver band side
D2 reading is fine. What is reading 0 and 1.62 ?
R113 and R114 should also have 44 volts present on at least one end of them.
R113 and R114 should also have 44 volts present on at least one end of them.
D102
I should have also measured the voltage on those resistors and the two little bronze diodes.
I should have also measured the voltage on those resistors and the two little bronze diodes.
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Start again.
D102 should have aprox 44 volts on both ends.
R113 and R114 should also have 44 volts present on one end of each.
If you have 44 volts on one end of each resistor and only a couple of volts on the other then its a good sign that the resistors have failed open circuit. They would then be checked with the amp OFF and by doing a resistance check across them. If they read incorrectly then remove them to measure them.
D102 should have aprox 44 volts on both ends.
R113 and R114 should also have 44 volts present on one end of each.
If you have 44 volts on one end of each resistor and only a couple of volts on the other then its a good sign that the resistors have failed open circuit. They would then be checked with the amp OFF and by doing a resistance check across them. If they read incorrectly then remove them to measure them.
resistor check
OK, checked those resistors
R105 = 0, 0
R106 = -45.2, -45.2
R107 = -45.1, -45.1
R109 = 1.6, 0
R110 = -0, -0
R111 = 0, 1.62
R112 = 0, 0
R113 = 1.64, 1.64
R114 = 1.64, 1.64
and diodes
D103 = -0.0, -0.00
D104 = -45.4, -45.4
I probably won't do much more this morning as I need to start work, unless ts quick.
And just to confirm, those infinite readings on Q105 and Q112 were out of range and just rechecked on 200V setting and they are all in the 45V range therefore E/C/O;-
Q105 = 0.02, -45.1, 2.4
Q112 = -45.1, -0.00, -45.1
OK, checked those resistors
R105 = 0, 0
R106 = -45.2, -45.2
R107 = -45.1, -45.1
R109 = 1.6, 0
R110 = -0, -0
R111 = 0, 1.62
R112 = 0, 0
R113 = 1.64, 1.64
R114 = 1.64, 1.64
and diodes
D103 = -0.0, -0.00
D104 = -45.4, -45.4
I probably won't do much more this morning as I need to start work, unless ts quick.
And just to confirm, those infinite readings on Q105 and Q112 were out of range and just rechecked on 200V setting and they are all in the 45V range therefore E/C/O;-
Q105 = 0.02, -45.1, 2.4
Q112 = -45.1, -0.00, -45.1
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I'll study those later but R159 reading is OK. One end goes to the amp output (0V still) and the other returns to the -44 volt rail via three separate paths. So that's OK.
OK, I just assumed the imbalance was a fault, thanks for clearing that up. I will put it away until later now, cheers.
Comprehensive test results
I have attached a pdf of all the results of measurements on good and bad side.
Some readings could not be taken because it kept shorting the amp (bulb dimmer set up was a saviour here I guess), and these are noted by a ***.
Whenever you get a moment.
P.S. I never shorted out that capacitor yet.
I have attached a pdf of all the results of measurements on good and bad side.
Some readings could not be taken because it kept shorting the amp (bulb dimmer set up was a saviour here I guess), and these are noted by a ***.
Whenever you get a moment.
P.S. I never shorted out that capacitor yet.
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