Denon AVR 1804 amp won't switch on

[73's de Edd]

CONDITIONS:

With an unpowered set, and with your DVM being in its DIODE test mode:

Q151: I am not getting a dead short between base and emitter but DMM does not show 0L but 1681

That range of 1681 is exactly what I would expect a good transistor to read.

CONDITIONS:

Now you must have powered the unit up and then found :

Q151:
DMM set to 200mV
Emitter: 0.3mV
Base: 8mV
Collector: 0.3mV

Those Q151 collector and base voltages are vewy-vewy FEEBLE.
Any chance of spot checking back at RED 3 and confirming its 5.6 VDC presence and then short
across Q151' s R159 base resistor and see if the voltage at Q151 collector then shoots on up towards that 5.6 VDC supply level .

 

[bushtech]

by short R159 you mean bridge across it's 2 legs?

 

[73's de Edd]

Base to emitter

 

[bushtech]

Thanks
"Any chance of spot checking back at RED 3 and confirming its 5.6 VDC": Yep 3 legs 16.6V, 0.6V and 5.6V
Sorry, confused: Am I meant to short base to emitter on Q151 or take out R159 by shorting it's legs

 

[73's de Edd]

.
You say . . . . .

This is as I am facing the round face of transistor: from L to R= E-B_C

Since B and E leads are side by side, a clean, shiny standard small screwdriver tip should be able to temporarily create a short between them for you.

 

[bushtech]

OK. Shorting out B to E, collector voltage drops to virtually zero on collector

 

[davenn]

Test point:
1=16.85V
2=16.62V
3=5.6V and 0.6V on base
4 & 5. I get 0V on all legs of Q151
6=0V
7=7.8V
8=15.76V
9=0V
10=0V
11=16.56V on both legs
12= 16.56V on centre leg other legs 0V

so why were you not getting those yesterday when you retested those positions for me ?

 

[bushtech]

davenn. I wish I knew. Either that fuse was blown or I was making a stuffup of the readings. It is very tricky taking the readings on the underside of the board. Apologies.


But Good Morning

 

[73's de Edd]

.


Sir Dave . . . . . .

Yesterday his juke box blew da fuse . . . .ICP-N15 opened up . . .ergo . . . .nuttin' got past our now assigned
RED 1 test point.


Sir bushtech . . . . . . .

Well doesn't that beat all ?
RED 4 should have 5.6 Volts on it unless either Q151 is turned on and its conduction grounds out that 5.6 voltage, or the less likely POWER_DOWN line that runs to the left.

My drawing reflects Dave's pre assigned, same color coding for the 3 . . . . Blue-Red-Yellow lines of interest.

Guess we will have to shed connections in order to see what is pulling the RED 4 5.6VDC down.
Start with lifting the collector lead of the Q151.

 

[davenn]

Dave . . . . . .

Yesterday his juke box blew da fuse . . . .ICP-N15 opened up . . .ergo . . . .nuttin' got past our now assigned
RED 1 test point.

YES, I knew he had blown the fuse and that's why I had asked to bridge it out with a small bit of fuse wire and retest

 

[bushtech]

Whoa! back up. Just realised I was shorting out legs on Q117


OK This time I got the right resistor. And shorting out E and B I still get 0V on emitter.
Will now lift collector leg of Q151


Collector leg of Q151 lifted

 

[73's de Edd]

Does that RED 4 now have close to that 5.6 VDC on it, with that transistor collector lifted ?

 

[bushtech]

Q151 voltages now: E=5.96V & B=5.48V

 

[73's de Edd]

.

Sir bushtech . . . . . . ..

I can see the + 15.76 voltage originating from RED 8 and back flowing through the D154 8.2 volt rated zener and then thru R160 and then ending up at the Q151 base.
BUT your Q151 emitter is connected to the same buss as your meters ground, which equates to 0 vdc.
You must have meant the just lifted collector.

Does that RED 4 just have ~ 5 VDC on it now, since it is now only consisting of that POWER_DOWN connection and the 4.7K resistor ?



73's de Edd

 

[bushtech]

St. Edd The lifted collector leg voltage now 5.37V
Base and emitter voltages as above


Just checked for continuity between base and emitter and with DMM on diode function it reads 689


So is the problem now the 5.96V on the Emitter?


Ok I see the problem. I must have my collector and emitter mixed up because I get continuity between our ground point on C158 and the hole where I lifted the leg of Q151

 

[bushtech]

Now lifted the opposite leg
So new emitter now 0V
Base 5.16V
Collector hole in pcb 6.3V
Collector on transistor 0.13V
Better?

 

[bushtech]

St. Edd
My apologies. Finally found the 2SC1740 (Q151) datasheet and I've still got it wrong.
Looking at round face of transistor the pinouts are from L to R:
1 Emitter
2 Collector
3 Base

Must admit I was stunned by this, never imagined the base would be anywhere but in the centre.

But before I pull the transistor again and start bending it's legs please confirm that I have finally got the pinouts correct.
Me very embarassed and apologetic
Thanks

 

[bushtech]

Q151
Working on the assumption that my reading of the pins as above is correct.

I have now pulled the centre pin (which I hope is the collector)

Readings:
1. = 0.68V
2. = 5.16V This is voltage on the board
3. = 0V (0.1mV)

The pulled collector pin of the transistor reads 3.3mV if that's of any relevance.

 

[73's de Edd]

WHeeeeeew . . . . . .

. . .we didn't need that dalliance to the side.

In not using the 1-2-3- numbering aspect of the Q151 transistor.




I am now expecting that the collector lead is free floating and that the base is connected and that the emitter is at ground buss potential..
In that case . . . . what voltage level is RED 5 now, as well as RED 4 ?

( I repeat the condensed schema below, to have same page referencing)

73s de Edd

 

[bushtech]

St. Edd Thanks
Looking at round face of transistor the pinouts are from L to R:
1 Emitter
2 Collector
3 Base
I am using this numbering as I believe it's correct

Confirmed
Collector is free floating
Base is connected and at ground potential
Emitter is at 0.68V

Red 4 = 5.16V

Red 5 = Here I have measured on both legs of R159 and I get about 0,68V on one leg and 0V on other leg.