Dead Aiwa AV-D50

[jworthin]

First post.
This Aiwa receiver does not power up. Checking supply voltages reveals the VM line is not coming up. Should be +11.6V. The power regulator transistors are not getting bias current via Q107 but I do not understand why. It seems the bias comes from circuits after the regulator transistors that are nearly turned off. These transistors and diode test okay.

Measured voltages:
Q109 E 26.35
B 25.77
C 1.470

Q108 E 26.35
B 25.77
C 1.470

Q107 B 0.385
C 25.78
E 0.005

Q106 E 0.0
B 0.0
C 0.385

Q105 E 1.330
B 1.309
C 0.0

D101 anode 0.0
cathode 1.370

Note the power transistors pass more current (as they warm up?) so some voltages tied to them that should be the same are slightly different as I measured them at slightly different times.

Any help would be greatly appreciated. I have been trying to figure this out for days now.

[petehall347]

Re: Dead Aiwa AV-D50

quick look says its very likely in protect mode .
is the negative rail ok ?

[jworthin]

Re: Dead Aiwa AV-D50

There are two relays RY101 and RY102 that when closed supply transformer AC to the B+- rail bridge and filters (about +-50V). The relays are not yet closed so the rails float at +-25V.

[jworthin]

Re: Dead Aiwa AV-D50

This unit has no separate stand by supply. I believe this VM voltage is used to feed further regulators for 3.3V and 5V for the power button and remote controller. I think it needs to come up first.

[petehall347]

Re: Dead Aiwa AV-D50

them damn pnp transistors always throw me out .. i fully understand npn ..pnp are a bloody nuisance ...

[budm]

Re: Dead Aiwa AV-D50

Can you please upload the full service manual?

[madan1]

Re: Dead Aiwa AV-D50

There you go... it looks like a total mess to me .. so glad the new receivers use much more simple voltage regulator circuits.

[jworthin]

Re: Dead Aiwa AV-D50

Aiwa AV-D50 SM

[jworthin]

Re: Dead Aiwa AV-D50

Is the biasing network R119, R120, R122 supposed to turn on Q108 and Q109 and then Q106 reduces over voltages based on the zener D101?

[budm]

Re: Dead Aiwa AV-D50

OK, I hope you can follow the operation of the circuit:
See that current sensing resistor R143? In normal operation, the current drawn by the load will not cause enough Vdrops on that R143 so NO BIAS for Q105 so it is OFF which makes Q106 to be OFF, so the Collector Voltage of Q106 will be high so Q107 is bias ON which will bias ON Q108, Q109. Q105, Q106 re part of the Latch/Protection circuit.
You only show part of the circuit so I really do not know exactly what you have and do not have.
If too much current flow through R143 then Q105, Q106 will be ON so Q107 will be OFF so Q108, Q109 will no longer have the bias to be turned ON.
Notes: Q108, Q109 are not completely turn OFF they are bias on a little by R119 so you will have little output Voltage to keep the protection/latch active until the you cycle the power to reset.

[budm]

Re: Dead Aiwa AV-D50

Aiwa AV-D50 SM

I get this message "Invalid Attachment specified. If you followed a valid link, please notify the administrator" when trying to download it.

[jworthin]

Re: Dead Aiwa AV-D50

The collectors of Q108 and Q109 are at 1.47V well under the 11.6V output needed. It seems like the over current protection circuit should not be activated. Also the base of Q106 is 0.0V. Seems like in this state Q108 and Q109 SB conducting.

The full manual is posted in #7. Please see page 18.

[budm]

Re: Dead Aiwa AV-D50

See post 11 as to what happen when I try to download your manual.
If the E-B junction of Q106 is at 0V, then what do you have on the Collector of Q106? 0.385V?
What is the feeding Voltage to the Emitter of Q108/109?

Once the latch is activated by the over current, the output will drop down to that low Voltage to keep the latch in place until you recycle the main power.

[budm]

Re: Dead Aiwa AV-D50

BTW, you need to test the resistance of R119: 4M7 resistor.

[jworthin]

Re: Dead Aiwa AV-D50

Please try the SM from #7 (madan1). That download works for me.
Collector Q106 is 0.385V (see measurements in #1)
I tried using my Fluke to record max current thru R143 on power up and there was no current surge. I also tried (risky) shorting R143 to prevent an over current detection with unchanged result.
Could you please explain the overcorrect latch? I do not understand how it works. Thanks.

[jworthin]

Re: Dead Aiwa AV-D50

R119 is 4.73M unfortunately.

[budm]

Re: Dead Aiwa AV-D50

Take out Q106, right now Q107 is not getting enough bias to be ON.

[jworthin]

Re: Dead Aiwa AV-D50

Do you think the .385V Q105 base should be biasing it on?

[jworthin]

Re: Dead Aiwa AV-D50

If I take out Q106 might the VM line shoot up to 25V? (Since that also takes out the zener regulation.) Could that blow out other parts?

[jworthin]

Re: Dead Aiwa AV-D50

I removed Q106 and the output voltage indeed goes up to the full 25V.

Does this mean Q106 was bad or the current protection WAS tripping somehow?