I wouldn't place too much emphasis on test results, often parts need a few volts/amps before they fail. Q47 is kinda working since the relay kicks in, this will probably be enough to fool most testers. If it fails testing then item is faulty. If it passes testing then item MAY be faulty.
yes it was a new KSA992- the only difference was the 2SA has a HFE of 550 or so and the KSA about 380 or so-
replaced Q47 with the original- no difference
I have tried to draw the circuit of the other two transistors (Q40 and Q41) not shown on the circuit.
Q40 is a 2SC2378 and Q41 is a 2SA954- both test good.
The voltages on each are:
Q40 e 0/ b 4v/c 0v
Q41 e 65.7 /b 65.7 /c 0
Q39 e 0 /c 2.2 rises to 4. then back to 2.2 etc /b 0 rises to .3 then back to 0
This really has me very confused
any help appreciated
I have tried to draw the circuit of the other two transistors (Q40 and Q41) not shown on the circuit.
Q40 is a 2SC2378 and Q41 is a 2SA954- both test good.
The voltages on each are:
Q40 e 0/ b 4v/c 0v
Q41 e 65.7 /b 65.7 /c 0
Q39 e 0 /c 2.2 rises to 4. then back to 2.2 etc /b 0 rises to .3 then back to 0
This really has me very confused
any help appreciated
Attachments
Your sketch needs some rework, you have Q41 e/b/c all connected/short.
Also the cap C28? does not make sense, probably -ve goes to GND?
Also the cap C28? does not make sense, probably -ve goes to GND?
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Thanks, completely understandable. Those 2 transistors are in play so need clear understanding, will look at figs a bit later.
Could you post a hi-res pix of this area including Q39-Q44, include both track and component side
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I got a similiar sort of pic.
From your voltages (Q41e=b=65.7) you may have a failed Q41 (b-e open?)
so the base voltage is supplied via R99 with "no" current flow. Has
Q41 been replaced? Q41c voltage (0V) looks wrong when looking at
Q40b (4V), recheck both.
From your voltages (Q41e=b=65.7) you may have a failed Q41 (b-e open?)
so the base voltage is supplied via R99 with "no" current flow. Has
Q41 been replaced? Q41c voltage (0V) looks wrong when looking at
Q40b (4V), recheck both.
Q41 is original and tests OK on the Peak transistor tester.
The voltages on Q41 are e 65v c0v b65v and on Q40 e 0v c 4v b 0v
peter
The voltages on Q41 are e 65v c0v b65v and on Q40 e 0v c 4v b 0v
peter
Suggest measure Q40, 41 b/c/e voltages to GND on the working unit.
Looking at the interwork of those transistors
The "speaker line" (Q25c...) should normally be low, less than +/-50mV.
That feeds into Rxxx and Q41b (not included in my pix so can't confirm).
Q41e(pnp) is fed by R102 and also connects to Q39c, Q42e rail. When Q41
turns on, voltage on Q41c will turn Q40 on and drag that Q39c/Q42e
rail down, so the Q41e voltage will fall and Q41 may turn off, so you
might get some cycling.
When Q39c/Q42e rail is dragged down would expect Q43,44 to turn off
then Q45 turns off so speaker relay releases. Voltage at Q43c goes to
near 71V rails voltage causing Q46, 47 to be incorrectly biased/turn
off so NFB relay releases.
Grateful if someone would correct me.
I would expect Q41 to be normally on
Looking at the interwork of those transistors
The "speaker line" (Q25c...) should normally be low, less than +/-50mV.
That feeds into Rxxx and Q41b (not included in my pix so can't confirm).
Q41e(pnp) is fed by R102 and also connects to Q39c, Q42e rail. When Q41
turns on, voltage on Q41c will turn Q40 on and drag that Q39c/Q42e
rail down, so the Q41e voltage will fall and Q41 may turn off, so you
might get some cycling.
When Q39c/Q42e rail is dragged down would expect Q43,44 to turn off
then Q45 turns off so speaker relay releases. Voltage at Q43c goes to
near 71V rails voltage causing Q46, 47 to be incorrectly biased/turn
off so NFB relay releases.
Grateful if someone would correct me.
I would expect Q41 to be normally on
on the good working unit:
Q39 e 0v c7.9v b 0v
Q40 e 0v c7.9v b 0v
Q41 e65v c0v b- trips relays when voltage is probed
Q41 is a 2SA954- and the wisdom is KSA916 is a good substitute- I have ordered some and will replace Q41.
I will keep probing
Q39 e 0v c7.9v b 0v
Q40 e 0v c7.9v b 0v
Q41 e65v c0v b- trips relays when voltage is probed
Q41 is a 2SA954- and the wisdom is KSA916 is a good substitute- I have ordered some and will replace Q41.
I will keep probing
On some emergency lights a 1uF/50V is used to control the battery switching to start the light if power goes.
You need to check if a tiny capacitor is used as the reservoir or timing capacitor. It may be with a bleed resistor to transistor base.
You need to check if a tiny capacitor is used as the reservoir or timing capacitor. It may be with a bleed resistor to transistor base.
@mbz- there is little doubt I need new eyes, and possibly a new brain as well- and lest not talk about knees......however Q41c is 0v on both units (even used two different DMM's to be sure).
As I am truly confused
The replacement for Q41 has arrived today, so I will install and report back
As I am truly confused
The replacement for Q41 has arrived today, so I will install and report back
It seems that Q43b being 1.2v is the key to turning on the relay coil drive circuits, as this appears to turn on both the NFB and spkr relay. I measured the speaker relay and it also is not getting coil voltage.
Q43b goes between 0.5v and 1.05v, and I think is not holding long enough for the timing circuits to charge and thus for the coil voltage to flow.
I pulled Q45- tests good, and replaced D34.
Unfortunately now the amp is now not even turning on- so I am thinking there could be a broken wire somewhere- all the AC fuses test good, so I will go hunting
Thanks again for reading and helping
Q43b goes between 0.5v and 1.05v, and I think is not holding long enough for the timing circuits to charge and thus for the coil voltage to flow.
I pulled Q45- tests good, and replaced D34.
Unfortunately now the amp is now not even turning on- so I am thinking there could be a broken wire somewhere- all the AC fuses test good, so I will go hunting
Thanks again for reading and helping