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Q46 is reading 66.5vdc from base and emitter, would this indicate it's shorted or would it be eat to remove and test it?
KrisBlueNZ
Sadly passed away in 2015
Sorry again. Yes, I agree with Bob, unless there's an intermittent problem and those most recent two sets of readings are with the circuit in different states.
The best way to check is to remove Q46 and measure the voltage across R108, positive probe to top end. If there's no voltage (or less than 0.5V), then R108 might be faulty, or there may be an intermittent problem. If the voltage is more than 1V, then Q46 is faulty.
The best way to check is to remove Q46 and measure the voltage across R108, positive probe to top end. If there's no voltage (or less than 0.5V), then R108 might be faulty, or there may be an intermittent problem. If the voltage is more than 1V, then Q46 is faulty.
Sorry kris what do you mean by top end?
KrisBlueNZ
Sadly passed away in 2015
Sorry, I'll be clear. Can you measure all of the marked points too.
So the short is not caused by Q46. It is either R118 or something on the circuit board traces.
With all due respect to Kris, I would still suggest that you pull one leg of R118 and see if it is shorted. But first maybe inspect the other side of the PCB to make sure there is no solder bridge there after you pulled Q46.
Bob
With all due respect to Kris, I would still suggest that you pull one leg of R118 and see if it is shorted. But first maybe inspect the other side of the PCB to make sure there is no solder bridge there after you pulled Q46.
Bob
KrisBlueNZ
Sadly passed away in 2015
Yes, there's something odd happeing there. It looks like R108 is shorted out, but I've never heard of a resistor going short circuit.
Can you power off the amp, and measure resistance across R108 (in circuit, probes either way round, preferably with Q46 still removed). It should measure about 1 kΩ, the marked value. If it measures short circuit (a few ohms or less), there must be a short somewhere on the PCB, possibly near the Q46 connection points.
Can you power off the amp, and measure resistance across R108 (in circuit, probes either way round, preferably with Q46 still removed). It should measure about 1 kΩ, the marked value. If it measures short circuit (a few ohms or less), there must be a short somewhere on the PCB, possibly near the Q46 connection points.
Arouse1973
Adam
Hello Bikemech
How did you measure the 66.2V, just curious. With respect to what terminal.
Thanks Adam
How did you measure the 66.2V, just curious. With respect to what terminal.
Thanks Adam
KrisBlueNZ
Sadly passed away in 2015
With respect to "T4" which is the 0V rail. The amp uses split supplies which aren't supposed to be that high, but the output transistors aren't fitted yet so there's hardly any load on the power supply.
ok set my meter to the 2000 range in the Ω section
R108 measure's 989 with the probes either way round
the amp was switched off and Q46 still removed,
R108 was still in circuit while testing.
i am going to remove the board again and look at the areas where i have changed componants, just to make sure i have not briged anything by mistake, will use the right chanel as a referance as that side seems to be ok
R108 measure's 989 with the probes either way round
the amp was switched off and Q46 still removed,
R108 was still in circuit while testing.
i am going to remove the board again and look at the areas where i have changed componants, just to make sure i have not briged anything by mistake, will use the right chanel as a referance as that side seems to be ok
Arouse1973
Adam
Oh ok, is that quite feasible for a 500W amp to drop 20 odd volts with the output transistors connected?
Cheers
Adam
Arouse1973
Adam
That's really odd, you measured 0 V across R108. That means either the meter didn't measure it correctly, the resistor is short circuit or it there is no current through it.
Adam
Arouse1973
Adam
Do you know what the +45VL reading is?
Adam
Adam
ok i now have something new happening!!!
have inspected the board and found a slither of copper from where the cable tidys push through the board, looked like it was shorting to or around R177,
removed this replaced Q46, (just pushed it into the pin recievers i fitted for test),
wired it up and turned it on, now i have the cooling fan on! this has never happened before, fault left is still lit tho,
also R108 measures 66.2VDC one side and 66.2VDC the other side with the negative probe to T4 0v rail
have inspected the board and found a slither of copper from where the cable tidys push through the board, looked like it was shorting to or around R177,
removed this replaced Q46, (just pushed it into the pin recievers i fitted for test),
wired it up and turned it on, now i have the cooling fan on! this has never happened before, fault left is still lit tho,
also R108 measures 66.2VDC one side and 66.2VDC the other side with the negative probe to T4 0v rail
Arouse1973
Adam
Do you measure different voltages now from last time. What is the voltage on the top end of R108?
Adam
Adam
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