You measure wherever is most convenient. Q106 E-B can be measured at any of the points that connect to Q106 as shown here. So Q106 emitter is the same point as Q108 emitter and also the same as the lower end of R115. Q106 base is the same point as Q116 collector and the lower end of R122.
The pins on the transistors are close together and one slip of the meter leads could be disastrous, that's why its easier measuring to surround parts.
The pins on the transistors are close together and one slip of the meter leads could be disastrous, that's why its easier measuring to surround parts.
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Yes, I noticed that the transistor pins were rather tight! I just wasn't sure to which end of the resistor I should go to. Thanks, will be trying later, maybe around 3.
OK, first measurement done on Q106.
Voltage from E (red) to B (black) was 7.1, with multimeter set to 20V.
It was a tight squeeze!
Voltage from E (red) to B (black) was 7.1, with multimeter set to 20V.
It was a tight squeeze!
You mentioned measuring all nodes (E,B and C) to chassis ground. Are we just referring to the case as a ground or a specific ground point on the board?
Lets stick with Q106 just for the moment.
Plus 7.1 volts with the red lead on the emitter and the black on the base ?
If that is so then Q106 is certainly faulty. You didn't mean 0.71 volts ? We have to be very very clear on the readings. If you have 7.1 volts then there is no doubt that the transistor is faulty.
Plus 7.1 volts with the red lead on the emitter and the black on the base ?
If that is so then Q106 is certainly faulty. You didn't mean 0.71 volts ? We have to be very very clear on the readings. If you have 7.1 volts then there is no doubt that the transistor is faulty.
Yes, it was 7.1
The second time when i took it from the resistors either side it started low and rose up and eventually settled on 7.1
When i did it direct on the transistor legs it was more immediate.
The second time when i took it from the resistors either side it started low and rose up and eventually settled on 7.1
When i did it direct on the transistor legs it was more immediate.
OK.
Now Q106 is a PNP device and the base emitter voltage when forward biased (normal mode of operation) can not exceed around 0.6 to 0.8 volts. For a PNP device the emitter is at the most positive potential of the three leads.
This 0.6 volts number that crops up all the time is cast in stone by the laws of semiconductor physics for silicon transistors. The base emitter junction should behave like a forward biased diode and the voltage should clamp at that value.
So that transistor is definitely duff based on what you say.
You need to be very careful replacing it. My advice would be to use a bulb tester and NOT to have speakers connected when working on this.
Now Q106 is a PNP device and the base emitter voltage when forward biased (normal mode of operation) can not exceed around 0.6 to 0.8 volts. For a PNP device the emitter is at the most positive potential of the three leads.
This 0.6 volts number that crops up all the time is cast in stone by the laws of semiconductor physics for silicon transistors. The base emitter junction should behave like a forward biased diode and the voltage should clamp at that value.
So that transistor is definitely duff based on what you say.
You need to be very careful replacing it. My advice would be to use a bulb tester and NOT to have speakers connected when working on this.
Just to confirm, i did it again..
- 7.15 (negative)
Multimeter on 20V setting, red on E and black to B
- 7.15 (negative)
Multimeter on 20V setting, red on E and black to B
Definitely faulty.
Now replacing that doesn't guarantee its all suddenly going to work but
lets see.
Now replacing that doesn't guarantee its all suddenly going to work but
lets see.Ok, peanuts for a replacement from farnell.
Although they have about 4 all with same specs. Maybe just different batches.
Although they have about 4 all with same specs. Maybe just different batches.
They are pretty generic parts tbh. The different designations relate to the packaging. I would get some of the BC546 complements as well.
Get the 'B' version:
http://uk.farnell.com/fairchild-semiconductor/bc556btf/transistor-bipol-pnp-65v-to-92/dp/2453802
Get the 'B' version:
http://uk.farnell.com/fairchild-semiconductor/bc556btf/transistor-bipol-pnp-65v-to-92/dp/2453802
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Yes, although i think there were 4 B versions but all seemed the same!
Just placed another order the other day, i should have waited!
Just placed another order the other day, i should have waited!
Weirder...
I double checked my soldering, touched it up a bit and tried again. I got a bit of sparking at the fuse (!) but it didn't blow. I tried it again and it has now switched on. Now to try the channels again...
I double checked my soldering, touched it up a bit and tried again. I got a bit of sparking at the fuse (!) but it didn't blow. I tried it again and it has now switched on. Now to try the channels again...
Ok, still the same symptoms as before. Left channel ok, right distorted and then cuts out when volume increased, goes to orange then resets and goes green again.
The fuse would not blow with a bulb tester and it would also save other parts from damage.
You say its still the same. Check again the base emitter voltage of Q106 and see if its still around negative 7 volts.
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