Denon AVR-1912 E2/EA

[Michael Studio1]

Well, I am totally out of my depth here, but switch it on and start feeling the transistors on the heat sink to see which are getting very hot

Well, Bushtech, thanks for that suggestion. With only 5 secs. to heat up I can't imagine any transistors showing evidence of over-heating. I do have a dedicated digital temperature meter though: "TWO K-TYPE" Microprocessor Digital Thermometer 6802 II - so anything is possible! Michael Studio1 UK 11:40GMT

 

[bushtech]

Well, it's getting hot enough to shut the system down so I'm pretty sure even the fingertip test will make you say: Ouch!

 

[Tha fios agaibh]

Well, it's getting hot enough to shut the system down so I'm pretty sure even the fingertip test will make you say: Ouch!

It thinks it's getting hot because the cpu input. It may not be hot at all, just reading funny voltages.

 

[Tha fios agaibh]

Michael can you measure the voltage at Tr_Thermal? I suspect it's being pulled high by one of the following;
Q403 (FL), Q427 (C), Q451 (SR), Q463 (SBL)
Each transistor has a resistor on their collector that could be pulled to isolate where the voltage is coming from.

For example, R412 could be pulled to eliminate the possibility that voltage isn't from Q104 for the FL circuit. Make note of voltage change before and after.
Eventually, you should find what is throwing the Tr_Thermal fault (Thermal B)

 

[Tha fios agaibh]

...all pots are to be adjusted one-after-the-other, and to go on through all 7 pots, or whether it is expected to wait 10 minutes and then just set VR401 to 3.0mV. before going on...

The former. All test points can be set 2mv at once. Then, after 10minutes or so when temp has stabilized, they all can be tweaked up to 3mv.
Obviously that isn't going to happen if you only have 5 seconds to work with.

I think you should put all these test points at 2mv for now so any measurements you make are close to convention.

 

[Michael Studio1]

Q451, or Q463 triggers the Thermal B.
I think Tr thermal is telling you a transistor is overheating. How many components are on that heat sink?
I predict some invasive surgery is warranted.

Thank you, John. Gosh! There's only a 'turned-on' time of 5secs. which gives me pause to wonder if any Transistor can heat up in that time. However the Service Manual says (Page 23. 2.2.) 'Protection history display' which indicates to me that the result I'm getting is the 'result of something which has happened and probably which caused the failure. This effect will, of course, be on-going until the failed component is fixed/replaced. Would this be your interpretation? As to your "How many components are on that heat sink?" the Parts List shows there are 44 Semi-Conductor Group (such as Q401 at Page106/D2 etc), 21 Diodes, 21 Zener Diodes, 86 Resistors, 7 Variable resistors (VR401-7), and 76 Caps. - some ceramic and the rest electrolytic. I have a Peak Atlas DCA 55 Semiconductor Component Analyser which, although not designed to analyse components that are in circuit, says any capacitor in a Cct must be drained of its charge. I have never had this 7Channel Amp. out of the AVR. Is this the information you are seeking? Michael Studio1 UK 14:52GMT

 

[Michael Studio1]

It thinks it's getting hot because the cpu input. It may not be hot at all, just reading funny voltages.

M-m-m-m. Yes. However the Test on page 23 shows 'protection history display' so it may well be showing the cause of the failure - and continue to do so until the failed component is replaced. Do you agree? But I have just posted amy thoughts about this above . . . Michael Studio1 UK 14:59GMT

 

[Michael Studio1]

Michael can you measure the voltage at Tr_Thermal? I suspect it's being pulled high by one of the following;
Q403 (FL), Q427 (C), Q451 (SR), Q463 (SBL)
Each transistor has a resistor on their collector that could be pulled to isolate where the voltage is coming from.

For example, R412 could be pulled to eliminate the possibility that voltage isn't from Q104 for the FL circuit. Make note of voltage change before and after.
Eventually, you should find what is throwing the Tr_Thermal fault (Thermal B)

OK, John. I haven't had this PCB out of the AVR before - so this may take a little while. Please advise where Tr_Thermal is to be found? I'll see if I can access it without pulling the PCB. Please give me a Page and Location. Plus, Page 56 gives the outline of that 7Ch. Amp. B'D - if that helps? Michael Studio1 UK 15:07GMT

 

[Michael Studio1]

Well, it's getting hot enough to shut the system down so I'm pretty sure even the fingertip test will make you say: Ouch!

Hello Bushtech! Thanks for your suggestion. It's quite possible that it isn't getting hot at all, but that the Thermal reading is but a 'history' of what has happened in the past to give an indication of where the problem lies. And it won't go away until it's fixed. ? My interpretation. Michael Studio1 UK 15:11GMT

 

[Tha fios agaibh]

First, I would put the test points back to 2mv, if you can.
Tr_Thermal is on CN8 pin 5, and a few other places,.... The amp board if i recall correctly.

If Tr_Thermal (Thermal B fault) has any significant voltage, it's safe to say it's an active fault.

Edit: See page 106.
CN404 pin5. Should be the same board with the pots and test points.

 

[Michael Studio1]

First, I would put the test points back to 2mv, if you can.
Tr_Thermal is on CN8 pin 5, and a few other places,.... The amp board if i recall correctly.

If Tr_Thermal (Thermal B fault) has any significant voltage, it's safe to say it's an active fault.

Edit: See page 106.
CN404 pin5. Should be the same board with the pots and test points.

Thanks John. Just had a little diversion - to lift up the Studio Steinway and put wooden castor blocks under the three castors. Now the pedals come off the ground! We're getting there! Right. Now to the real work-in-hand. Since there's a 5 second window - all being well these TP401 - TP407 can be adjusted to the first required +2V. as per Page 56. Question: MODE : MCH STEREO - what's "MCH" it doesn't seem to be one of the Modes available.
Michael Studio1 UK 17:23GMTea-time!

 

[bushtech]

Multi channel stereo as opposed to 2 ch stereo?

 

[Michael Studio1]

There's nothing to indicate, when adjusting the VR's, whether the 2mV. is taken from TP pin1 - 3 or from pin1 - AGND and from pin3 - AGND. Just shows my ignorance (and need for help!) Michael Studio1 UK 17:35GMT

 

[Tha fios agaibh]

Thanks John. Just had a little diversion - to lift up the Studio Steinway and put wooden castor blocks under the three castors. Now the pedals come off the ground! We're getting there! Right. Now to the real work-in-hand. Since there's a 5 second window - all being well these TP401 - TP407 can be adjusted to the first required +2V. as per Page 56. Question: MODE : MCH STEREO - what's "MCH" it doesn't seem to be one of the Modes available.
Michael Studio1 UK 17:23GMTea-time!

Never understood piano pedals. At least they didn't help my playing. lol.

MCH = Multi Channel

2mv, Not 2V, Right?

 

[Michael Studio1]

Multi channel stereo as opposed to 2 ch stereo?

Yes, Bushtech - that seems very likely! I didn't think of that! Thanks. Michael Studio1 UK 17:51GMT

 

[Michael Studio1]

Never understood piano pedals. At least they didn't help my playing. lol.

MCH = Multi Channel

2mv, Not 2V, Right?

Yes. I understand pedals more than mV. I fear. Michael Studio1 UK 17:54GMT - where's my TEA!?

 

[Tha fios agaibh]

"There's nothing to indicate, when adjusting the VR's, whether the 2mV. is taken from TP pin1 - 3 or from pin1 - AGND and from pin3"

Michael, put your spectacles on.

 

[Michael Studio1]

The three-socket micro-plug I made up seems to have had a mal-function - pin(socket) 1 had come out and the retaining black plastic finger which keeps the copper connector in place has broken off. I have glued it all up with Cyano Acrylate - so it'll be a little while b4 I get going again. Michael Studio1 UK 18:08GMTttttt-time!

 

[Michael Studio1]

"There's nothing to indicate, when adjusting the VR's, whether the 2mV. is taken from TP pin1 - 3 or from pin1 - AGND and from pin3"

Michael, put your spectacles on.View attachment 40065

Gadzooks! When looking at the Service Manual I not only wear my spectacles but also (because the designation of Connector Blocks is so small) I have one of those magnifying headbands + a single magnifying glass which can be swung out in front of one eye. With all this magnification I still didn't notice that little drawing !! More mea culpa.
Many thanks for pointing this out, John. Now the CA must be dry, the Tea hot and I'm ready to go mV.-wise. The MODE is: AVSurround. Adjusting Idling Current All but TP406 are adjusted to 2.0mV. TP406 gives no reading at all - just the usual 'OL' indicative of the meter not being connected. Do we first address this issue before going on to CN8 pin5? Michael Studio1 UK 19:19GMT

 

[Tha fios agaibh]

MODE is: AVSurround. Adjusting Idling Current All but TP406 are adjusted to 2.0mV. TP406 gives no reading at all - just the usual 'OL' indicative of the meter not being connected. Do we first address this issue before going on...

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).