help finding a transistor

Status
Not open for further replies.
Jump to Latest
#4
I don't have a high mpixel camera to take a photo os such a small part, but the script is as follows:
MTJ
279H
EBC

it is on the same circuit board as two power transistors TIP41A so I'm guessing it is functioning as a driver transistor. This is found in an old Italian organ and there are many others of this same transistor in other sections of the circuitry. Sadly the schematic for this model of the organ is quite different from this particular version, the power amp and power supply have very different layouts and parts, though I do notice that in the schematic most of the transistors are BC209's in all sectors whereas on the circuit boards there are various types, would the BC209 be an option driver transistor?

thanks
 
#5
Looks like this would have to be some general purpose type. Can you tell whether it's pnp or npn?

Your organ must be newer than the schematic. BC209s are quite old and in TO-18 package. These would be pnp. In somewhat newer devices one would expect to find BC559 instead. 2N5087 (still made by ON Semi today, btw) would also work.

If in doubt, just trace out the schematic. I would expect a small-signal pnp like this at the very input of the power amplifier. Then a VAS (maybe small-signal or high-voltage), then bias and drivers (typically medium power types), and finally outputs (the TIP41s - looks like it's a quasicomp output stage). BTW, if the input transistor is toast, I would look very hard at the output stage as well.
 
#6
Yes I think you are right, the schematic dates 74-75 whereas the organ had caps from 76-77. Maybe this can help a little bit:
The 7 transistors shown in the power amp\supply section on the schematic:
1 x MTJ10S
1 x BC303
2 x BC301
1 x BD587
1 x BD597
1 x BC178

The 7 transistors in the organ are:

2 x BC301
2 x TIP41A
1 x BC320B
1 x BC303
1 x TJ729H

I will try to draw a schematic following the circuit board and try to shed some light so that I can help you help me

thanks
 
#9
tracing the circuit from the bridge rectifier to the first transistor, the main voltage rail is basically the same as the schematic, the TIP41A takes place of the BD587 and uses 0.33ohm 3 watt resistors instead of the 0.15ohm resistors shown on the schematic. Following on the 44v rail we get the first BC301 transistor. Then tracking back the TJ729H I confirm that it is in place of the MTJ10S transistor on the schematic.
 
#13
jimmy74 said:
yes but the problem is that not knowing what transistor this is, how do I know which is the base?
Click to expand...

The base is the terminal that gives the same diode reading to BOTH other leads. The base is usually the center of the three terminals.

Put the red probe on the center terminal. If it beeps to BOTH of the other terminals, you have a NPN type with the base in the center.

If not, put the black probe on the center terminal. If it beeps to BOTH of the other terminals, you have a PNP type with the base in the center.

If neither of these work, do the same with one of the other terminals.
If that doesn't work, repeat with the remaining terminal.
 
#14
jimmy74 said:
yes but the problem is that not knowing what transistor this is, how do I know which is the base?
Click to expand...

From your first post, the case has printed on it: MTJ 279H EBC.
This means that the lead closest to each letter is identified, so from left to right you have emitter, base, and collector. This is typical.
 
Last edited:
#15
ok with the flat face of the transistor facing me, and the tester on diode setting (it doesn't beep though, it beeps only on the 200ohm setting) it seems as though the left lug is the base because if I place the red probe on it and the black probe on the other 2 pins (one at a time) I get 320ohms but the readings keep rising, this also happens if I invert the probes though readings start at around 300 ohms.
 
#16
hmm ok then maybe I'm missing something here, doing as you suggest but not having a tester that beeps on the diode setting, I'll tell you reatings I get:

red probe on central pin
pin 1 = 0 ohm
pin 2= 308ohms and goes up steadily

same thing with black probe on central pin
 
#17
jimmy74 said:
ok with the flat face of the transistor facing me, and the tester on diode setting (it doesn't beep though, it beeps only on the 200ohm setting) it seems as though the left lug is the base because if I place the red probe on it and the black probe on the other 2 pins (one at a time) I get 320ohms but the readings keep rising, this also happens if I invert the probes though readings start at around 300 ohms.
Click to expand...

Don't let this fool you, almost certainly the leads are EBC per the label. It's likely a NPN, but you may have to desolder it to properly test.
 
#19
jimmy74 said:
unsoldered it no readings with black or red probe on center pin to one other pin, not even on the 2 Megaohm setting, and 0 ohm with black or red probe on the center pin to the other pin
Click to expand...

Well, either your meter is bad or the transistor is. Can you try it with another meter? You could even go to Radio Shack and try it on one of theirs.
 
Status
Not open for further replies.
Top Bottom