am i tsting this with the board powered up? or do i need the power off? and am i voltage testing or diode testing, ?
Test with the board powered up, and measure voltage.
also would any of the transistors i have already removed be any good as a replacement for Q6 as long as it was good?
Yes, Q11 and Q22 were MPSA92s. If the old ones measure OK out of circuit you can use them. Test them on the diode range of your meter. You should measure two diodes inside them, as in the PNP part of the second image in post #120. The correct measurements for a PNP, using diode range, are:
Black probe to base, red probe to emitter: should measure a diode forward voltage (about 0.5~0.8V).
Black probe to base, red probe to collector: should measure a diode forward voltage.
Red probe to base, black probe to emitter: should measure open circuit (indication of "1 ." or "0L" or similar).
Red probe to base, black probe to collector: should measure open circuit.
Collector to emitter: should measure open circuit both ways round.
i am going to do this test agin, i am sure i didnt have a negative sign on the bottom half of the circuit, i did take note you said add this if it was there! going to go back to post #115 and re read and retest to make sure i have done everything right
OK, good.
i have a problem with the word relative!! can you describe it another way?? do you mean more than , less than,
sorry but please dont for get i am a beginner, well sort of now lol
OK. Voltages are always measured
between two points. Like distance, which you would measure with a ruler. The distance between my nose and my chin is about 7 cm, but in electronics, the polarity (direction) is also important, so I would have to say that my nose is 7 cm higher than my chin. (This explanation always assumes that my head is upright.)
I can then say various things about the relationship between these two points:
- My nose is higher (more positive) than my chin;
- My nose is 7 cm (7 volts, for example) higher (more positive) than my chin;
- My nose, measured relative to my chin, is +7 cm
- There is 7 cm between my nose and chin, with my nose being higher (more postive).
In this case we're talking about differences in voltage, where both ends of the measurement are at specified points. This corresponds to the red-and-black boxes that I drew on the schematic in post #112. There are also some red boxes, where I want to know the voltage
at that point, measured relative to the 0V ("zero volt") rail of the circuit.
The 0V rail is a standard reference point for voltages to be measured relative to (also called "with respect to" or "with reference to"). It's kind of like sea level, or ground level, for the whole circuit. It is the default reference point for voltages that are said to be "at" or "on" a certain point in the circuit. That's why the black lead of the multimeter is often connected to the 0V rail of the circuit when you're making voltage measurments.
For example, if the ground or floor is the reference point, my chin is at about +150 cm. Therefore my nose is at about +157 cm. So have another look at that part of the circuit:
If that circuit was working properly, Q6's emitter (top terminal) would be at about +54V (relative to the 0V rail). Since an active transistor has about 0.7V between its base and emitter, and in the case of a PNP transistor (which Q6 is), the base is 0.7V more negative than the emitter, the base voltage would be (54V - 0.7V) = 53.3V.
I could have asked you to measure the individual voltages on those two points, relative to the 0V rail. But it's more interesting, and more accurate, to measure the actual voltage across the points. Just like if you want to know the distance between my chin and my nose, you wouldn't measure from my feet to my nose, then measure from my feet to my chin, and subtract them; it's better to measure the small distance directly.
I'm not sure whether this is helping, but I think it should. The important things to remember are that voltage is always measured between two points; the polarity of the voltage is important; if you're asked to measure the voltage "at" or "on" a specific point in the circuit, you need to measure it relative to the 0V reference rail.
