Denon AVR-1912 E2/EA

[Tha fios agaibh]

We are getting very close I think.

Tp406 could be 0v because either Darlington Q464 or Q470 is open.
Also, nearby Q463 base is likely being pulled negative which would forward bias it to send the Tr_Thermal fault.

You need to look over this circuit, and I need coffee asap.

BTW, what does CA stand for?

 

[bushtech]

Cyano Acrylate

 

[Tha fios agaibh]

Thanks bushtech, I thought for a moment Michael was talking about Tea and scones.
Lol

 

[bushtech]

Heh, only a pleasure. Just trying to help to speed this process up

 

[Tha fios agaibh]

Power rail to that portion of the circuit is "HighB".
What voltage do you get +HighB to HighGnd? How about -HighB to HighGnd?

I suspect + will be a bit high, and neg a bit low. Another words, Neg is being diverted to ground. And also suspect this portion of the circuit (SBL) as the cause provided you can't get a reading on Tp406.

 

[Michael Studio1]

Next day. I have pulled the 7CH AMP B'D and massive heat-sink. Looking for the transistors on SBL channel. TP406 gave no reading. ergo something is wrong there. CN8 is on the HDMI B'D - a 1yellow/4 black ribbon cable from one end of the 7CH AMP B'D. Its connector half-obscures its designation, but seems to be CN404. Printed on that PCB are: pin1(yellow)DC DET4. pin2 DC DET3, pin3 ASO DET, pin4 RADI THERMAL, pin5 TR THERMAL. Now I see it on page106/O6. Excuse me nattering on - this is all very revealing. Each Channel has 11 transistors (according to the Cct.Diag.) but in reality each Channel has 4 pcb mounted (with provision for 2 more which are identified) and 3 heatsink mounted. The heatsink mounted transistors are not identified on the PCB (unusual). Taking Channel SBL with its non-operating TP406, the Transistors actually mounted are: Q466, Q467, Q472, and Q461. Provision is made for: Q471 and Q462. Noted on the Cct.Diag. these two unmounted Transistors are marked as 'OPEN'. Note: Q470, Q464 and the trio at the Left end of SBL: Q461, Q467 and Q468 are not on the 7CH AMP PCB. Three of them must be those mounted on the Heatsink - but which ones I can't tell without dismantling the PCB from the Heatsink. The fate of the remaining 2 Transistors on each Channel is a mystery - which I am hoping someone will solve and advise! Michael Studio1 UK 10:44GMT

 

[Michael Studio1]

I need to re-read procedure but,... doesn't it have to be in MCH Mode before adjusting?
If it's not in the proper mode, the proper channels may not be active.

Yes I agree, TP406 should be addressed first. The voltage has to be going somewhere.

The good news is, if you end up knee-deep in this part of the circuit, you can always compare your measurements with another channel (same circuit).

Thank you John. There is no MODE MCH, (at least so my limited 5 secs. access to that MODE SETTING showed) so I presumed that MCH is AVSurround. The burning question is: What is the identity of the TWO + ONE Transistors mounted on the Heatsink? And, in the case of our SBL Channel, where are Q464 and Q470 mounted? They are both in the immediate Cct. of TP406. Michael Studio1 11:03GMT

 

[Michael Studio1]

We are getting very close I think.

Tp406 could be 0v because either Darlington Q464 or Q470 is open.
Also, nearby Q463 base is likely being pulled negative which would forward bias it to send the Tr_Thermal fault.

You need to look over this circuit, and I need coffee asap.

BTW, what does CA stand for?

It's a fast-setting plastic glue (don't touch it - it's also used in hospitals instead of stitches - but does come off eventually) I have frequently used CA Glue in pianos to fix loose tuning pins. It has a multiplicity of uses and comes in different viscosities. Worth getting a tube from a hard-ware shop to experiment with. My repair to that 3-pin test-plug was a successful case in point. Michael Studio1 11:13GMT

 

[Michael Studio1]

Right about the Coffee. I use fresh-ground strength 5 in my high-pressure 'La Pavoni' Cappuccino maker. (look it up - coffee will never be the same again for you!) It's amazing how much stronger this machine makes the same amount of ground coffee made in a Bodum! Michael Studio1 UK 11:19GMT

 

[Tha fios agaibh]

Your 4 board transistors check out with the circuit.
I suspect the 3 heat sink transistors are;
the 2 Darlington Q464 and Q470, as well as Q469 used for their biasing.

What should also be somewhere around there (on pcb) is Q463 that is to detect Tr_Thermal fault.

 

[Tha fios agaibh]

There is no MODE MCH

Thought there was a multi channel mode?
Neveryamind. I believe you should have all your test points regardless because all channels have the same rail. (HighB+/-)

 

[Tha fios agaibh]

It's a fast-setting plastic glue...I have frequently used CA Glue in pianos to fix loose tuning pins. It has a multiplicity of uses

Ok, It's known as "Super glue" over here.

 

[Tha fios agaibh]

I was suggesting you check HighB rail, but if you have everything torn apart.... we should either fish or cut bait.

I highly suspect this portion of the circuit so you might as well get in there and start checking components.

 

[Michael Studio1]

Your 4 board transistors check out with the circuit.
I suspect the 3 heat sink transistors are;
the 2 Darlington Q464 and Q470, as well as Q469 used for their biasing.

What should also be somewhere around there (on pcb) is Q463 that is to detect Tr_Thermal fault.

Q463 is not on the 7channel pcb - and not in the SBL area. So what detects Tr_Thermal fault then? As I have the 7Ch.Amp.PCB out of the chassis, I am going to try my Peak Atlas DCA55 semi-conductor component analyser on all 21 heatsink mounted transistors - see if any don't comply. Michael Studio1 UK 14:05GMT

 

[Michael Studio1]

Later: Although the Peak DCA Transistor Tester is intended for out-of-Cct. use I conducted 3 tests on all 21 Xistors The results were to compare all Channels against SBL Channel. Result: All three SBL Xistors are faulty. This doesn't help find Q463 . . . !! Michael Studio1 UK 15:00GMT

 

[Michael Studio1]

Interestingly, the results for Transistor 1 of all Channels (with the exception of Channel 6 SBL) was the same as were the results of all Transistor 3. Transistor 2 of Channel 6 was doubtful - so must also be changed. What caused these to 'blow' anyway? This must have happened when I was conducting the Page 56 Tests. - Adjusting the Idling Current. Michael Studio1 UK 15:14GMT

 

[Michael Studio1]

I was suggesting you check HighB rail, but if you have everything torn apart.... we should either fish or cut bait.

I highly suspect this portion of the circuit so you might as well get in there and start checking components.

Thanks, John. What constitutes the HighB rail? Which page is it on? How 'high' is 'high'? Michael Studio1 UK 15:29GMT

 

[Tha fios agaibh]

You've already dug into the board so I wouldn't worry about that now.
I haven't traced HighB to its source to find its voltage. It could be 7,5 or even 3.3v idk.

Looking at Q463 gave me the impression it's looking for a negative voltage imbalance to send a Tr_Thermal fault. Even without Q463, you have the same triggering transistors on adjacent channels that would also detect the imbalance because they are sharing the same rail. I may be wrong but that's my interpretation.

Edit: See CP403 on page 106.

I don't think you caused a transistor to fail by just adjusting the idle current. But was this channel known to be working fine before digging into this?
Which transistor failed? Tested out of circuit? What is the mode of failure?

 

[Michael Studio1]

Your 4 board transistors check out with the circuit.
I suspect the 3 heat sink transistors are;
the 2 Darlington Q464 and Q470, as well as Q469 used for their biasing.

What should also be somewhere around there (on pcb) is Q463 that is to detect Tr_Thermal fault.

RE: Q469. If this is the middle Transistor of the three in all 7 Channels, I have removed it (and the ones on either side) being careful to note which Transistor came from where. Then to check on the Part List - Page 173. This is where things get interesting. On removing the smaller Transistor (the middle one) I found it had no markings at all. I looked at the Cct.Diag. p107/G7 to check the identity of Q469(2SC3964) then checked the Parts List - page173 only to find it's not there! Of the trio of Heatsink Transistors, the one on the Left is: SK D2390 13 P and the one on the Right is: SK B1560 13 P. Since there doesn't appear to be any reference to these Transistors other than your surmise Q464 and Q470 I have looked at the Parts List and found they are not mentioned either. Now all three are desoldered and removed I can check them with the PEAK DCA55. Results: The small unmarked Transistor shows: NPN Silicon Transistor. (with the DCA55 it doesn't matter which connector goes where) The D2390 shows: Short Cct on all three connectors. The B1560 shows: Short Cct. on Collector/Emitter. Michael Studio1 UK 16:26GMT

 

[Tha fios agaibh]

Hey, great find!!
I woud download data sheets and compare the missing transistor number(s) with the transistor specified on the print.

Btw, HighB originates on page 108. It looks to be a 7v rail.

Yay. Its exciting to find fried components! Well, that or I'm just a geek.