Denon AVR 1804 amp won't switch on

[bushtech]

Dave
I replaced diodes:
D153
D143
D152
D149
D150

Checked them all once off board and they all checked good.
Then remeasured voltage across C158 =17.1V
Which I assume is correct voltage
Now thinking that I might have forgotten to push the on switch when I powered up. Duh!

 

[davenn]

Checked them all once off board and they all checked good.
Then remeasured voltage across C158 =17.1V
Which I assume is correct voltage
Now thinking that I might have forgotten to push the on switch when I powered up. Duh!

OK good

Possibly either that or one or more were failing under powered load, or maybe there was a dry joint on one of them
and that was remedied with the unsoldering and resoldering the new ones .... as can be seen , a few options

Still want to measure IC 105. Is that also across it's 2 legs?

now you can see if any voltage is coming out of this fuse

negative lead on the C158 negative and positive lead on either side of IC105


Dave

 

[bushtech]

Good Morning Dave
barring a serious parallax error between the top and the underside of the board I'm also getting 17.1V between neg leg of C158 and between either of the legs on IC105

 

[davenn]

Good Morning Dave
barring a serious parallax error between the top and the underside of the board I'm also getting 17.1V between neg leg of C158 and between either of the legs on IC105

good morning

OK good
next is to check either side of R151 located directly above the sun trans on the PCB
that takes power directly to one side of the relay coil

 

[bushtech]

Hullo? Getting 0V over R151 (R151 is a metal film 68Ω 1/4W resistor) What's interesting is that it's countersunk in a cutout on the board. Any idea why?


Solder on one leg of resistor dull grey. Gonna resolder


Nope, still 0V

 

[davenn]

Hullo? Getting 0V over R151 (R151 is a metal film 68Ω 1/4W resistor) What's interesting is that it's countersunk in a cutout on the board. Any idea why?

for ALL these DC tests keep the negative meter lead on the C158 negative terminal
so again, probe each side of the resistor with the red leg

it appears to possibly be a fusible resistor

 

[bushtech]

Ah Better. Both legs of resistor around17.05V

 

[bushtech]

Resistance of resistor measures 68Ω

 

[davenn]

Ah Better. Both legs of resistor around17.05V

Resistance of resistor measures 68Ω

OK good and did you measure right through to the relay pin ?


Im starting to fear that the voltage drive to the base of the transistor that switches the relay may not be there .... it is controlled directly from the CPU chip

 

[bushtech]

Nope. Will now trace the circuit to see what you mean

 

[bushtech]

Yep, continuity and 16.9V between cap and relay coil

Can we now safely assume the relay is fubar?

 

[bushtech]

Ooops , didn't see the part of your post about the CPU

 

[davenn]

check the voltage on the base pin of Q116 .... beside the relay


Im out for the next 3 hrs see ya later

 

[bushtech]

Thanks Dave. Will do tomorrow. Time for some old bones to rest

 

[bushtech]

17.2V on B.
0V on C & E

 

[davenn]

17.2V on B.
0V on C & E

home again sunday morning church and lunch done

I wouldn't have expected 17V on the base maybe just a few volts ... Emitter will be zero as it's going to ground ( PSU 0V rail)
am wondering if you have C aa B mis-identified ... are they marked on the PCB ?


D126 and the relay come off the collector
and there is a resistor between the base and emitter

 

[bushtech]

Aah yes. Thought base was in middle but datasheet shows it's RH leg looking from the flatside of transistor.

So that voltage measurement was on collector

 

[davenn]

Aah yes. Thought base was in middle but datasheet shows it's RH leg looking from the flatside of transistor.

So that voltage measurement was on collector

OK so that infers that the relay coil is OK

OK where to next ......

IC103, it is a 7805 voltage reg .... it supplies a power rail to the CPU that the CPU then switches and sends back down to that transistor you just tested

so you should have 17V in the input to the 7805 and 5V on the output

 

[bushtech]

Yup. 17.1V & 5.6V

Man, is this thing leading us a merry chase!

 

[bushtech]

So the relay is 12VDC but we keep seeing 17V. Isn't that a bit odd?