DENON AVR-1912 Tracing Paths and Losing GND!

[Michael Studio1]

This is an attempt to trace a GND Cct. through a cube of interconnected pcb's from the Denon AVR-1912. The reason for this strategy is to enable access to the salient test points on those pcb's. In particular I have lost the GND continuity which is essential to firing up the various IC's on these boards. Therefore the AVR doesn't work. This particular GND Cct. is that which starts at Page111/D10 of the downloadable Denon AVR-1912 Service Manual. Being able to enlarge this on the computer monitor and use the tool 'Ctrl+F' to search for any component in the device and find that component has been high-lighted in Blue is a tremendous help. Every Schematic and Printed Wiring Board for the AVR has reference points - like the 'X' and 'Y' for a graph - on each page - hence being able to refer to Page111/D10 immediately you find CN13A connector. So this trace is starting from pin4 on CN13A and one of the two DVM probes is attached to it. This is 'AGND'. I soon land up in a quandary of a collection of resistors - all seemingly wired together - on Page114/K5. Here is the problem: I have found (through utilising Ctrl+F) each or these 6 resistors and have heard the 'beep' from the dvm. However, getting any further is a problem. It would appear that AGND goes immediately to Page114/O3-4 (CN401) but it doesn't arrive. Neither does it arrive at P114/J5 - C823 and C825 which, according to the Cct.Diag. are clearly on the AV_B'D yet physically (according to Ctrl+F) are on the HDMI_B'D - and so they are in fact. But AGND is not there as per the dvm. So here's a question I must ask: When, in a Cct.Diag. a gaggle of 6 resistors are grouped and connected to a green GND path, are any paths which CROSS another green GND path actually electrically connected? If so that gaggle of 6 resistors makes no sense! Michael Studio1 UK 13:41BST 06-06-2016.

 

[bushtech]

Is this the bunch of resistors? (Might make it easier for somebody to figure out)

 

[Michael Studio1]

Is this the bunch of resistors? (Might make it easier for somebody to figure out)

View attachment 41382

Yes - that's the bunch, Bushtech. I see I should have magnified the Cct. Diag. more - to see the blobs (or lack of blobs). Thanks! Now I can go forward a bit! I'll be very glad when my other Cataract is operated on! Michael Studio1 UK 17:10BST 06-06-2018

 

[Michael Studio1]

Looking at that bunch of 6 resistors on Page114/K5, how does one interpret 'OPEN' ? It is a term frequently used in this Service Manual but has no meaning to me. I have physically found these resistors (which means 'OPEN' doesn't indicate they are not there) and get continuity from one end of all six - back to CN13A on Page111/D9. But I get no further in my quest for onward continuity of AGND to CHASSIS_GND. Unless, of course, this is where the break - or OPEN - is!! Michael Studio1 UK 18:19BST 06-06-2018

 

[Harald Kapp]

Why start a new thread?

 

[Michael Studio1]

Have you ever been driving to a town, not knowing the area at all, being in the town and driving out of it - the next finger-post indicator tells you the town you're looking for is behind you . . . ! That's what looking for an OPEN in the GND quest is like! Michael Studio1 UK

 

[Michael Studio1]

Why start a new thread?

Hello Harald - Starting a new thread was suggested by Kelly's_Eye who said:
↑
I have to admire your tenacity and determination though!
I wouldn't suggest you STOP what you're doing - as a semi-retired person myself I charge £25 to fix electrics/electronics regardless of how long it takes me as 'time' is something I have plenty of (within the confines of the grim reaper that is ).

I was speaking in respect to (potential) frustration - not only to yourself but to those contributing to the thread as you may eventually find yourself to be the only contributor! Looking through the thread I can see this happening now.....

But, specifically, when a thread runs past a given number of pages there will be few people who have the time and/or inclination to trawl through dozens of pages to get a grasp on the situation enough to be able to offer an input - this is why I said I'd 'lost interest'.

It may be helpful (to yourself and others) to break the problem down and have separate threads for each - linking (by posting clickable links) - where it is necessary to join up details.

Even now, as much as I tend to drop in on the thread to see where it's going I (seriously) haven't got the will to review it ALL so assistance, where I might be able to offer it, is sadly lacking.

Might I then suggest you 'start again' with thread(s) titled

DENON AVR - DISASSEMBLING;
DENON AVR - PSU;
DENON AVR - DIGITAL;
DENON AVR - ANALOG etc etc.....

and tackle the various issues individually where you're more likely to get (and keep) interested parties?

So I thought maybe he has a point.
However, Harald, as Mentor - if you feel this was a wrong decision and it would be best to stop the new thread and dump it all into the original thread (if that's possible) it will give continuity to the history of this projected and prolonged repair. Thanks for asking - That's the reason. Michael Studio1 18:44BST 06-06-2108

 

[kellys_eye]

Might be worth reading through this article on Analog/Digital grounding (and the techniques used).

http://www.analog.com/en/analog-dialogue/articles/staying-well-grounded.html

 

[Michael Studio1]

Might be worth reading through this article on Analog/Digital grounding (and the techniques used).

http://www.analog.com/en/analog-dialogue/articles/staying-well-grounded.html

Thanks, Kelly's_Eye. Good Night-time reading? Michael Studio1 UK

 

[Michael Studio1]

I have just printed this - as being my best way to ingest information. Looks like an interesting article.
Thanks for suggesting it. One thing I am about to do is tackle the AGND from the other end - see where it goes from CHASSIS_GND. Michael Studio1 UK 19:32 - when my brother was born!

 

[davenn]

Why start a new thread?

because it was suggested that after 600+ posts in the original thread it was getting VERY difficult to follow
and that maybe breaking the problem down into smaller bites to check out may be a good idea

I tended to agree that that sentiment


Dave

 

[davenn]

However, Harald, as Mentor - if you feel this was a wrong decision and it would be best to stop the new thread and dump it all into the original thread (if that's possible) it will give continuity to the history of this projected and prolonged repair.

It is a good decision, as I stated above

 

[Michael Studio1]

It is a good decision, as I stated above

OK! But I don't want confusion - there's enough in this AVR! Talking of which may I suggest looking in the Service Manual at Page114/A3 - wiring traces between pages. See RET_GND _________ its lead is coloured Green. Now look at where it's going to: Page116/O7 RET_GND __________ its lead is BLACK. Confusing? (yes) for this is the very same GND from Page114/E1 CN14pin18-19 which trace back through the SIDE_CONT (Page111) to the REGULATOR B'D (Page110) and CP13A pin4-5 with its origin source of AGND from CP104pin2 (Page110/N9) This is the GND which gets lost somewhere on Page114 and which is causing all the problems - IC30 and IC801 not firing up &c. Possibly other problems too. Michael Studio1 UK 12:47BST 07-06-2018

 

[Michael Studio1]

OK! But I don't want confusion - there's enough in this AVR! Talking of which may I suggest looking in the Service Manual at Page114/A3 - wiring traces between pages. See RET_GND _________ its lead is coloured Green. Now look at where it's going to: Page116/O7 RET_GND __________ its lead is BLACK. Confusing? (yes) for this is the very same GND from Page114/E1 CN14pin18-19 which trace back through the SIDE_CONT (Page111) to the REGULATOR B'D (Page110) and CP13A pin4-5 with its origin source of AGND from CP104pin2 (Page110/N9) This is the GND which gets lost somewhere on Page114 and which is causing all the problems - IC30 and IC801 not firing up &c. Possibly other problems too. Michael Studio1 UK 12:47BST 07-06-2018

I have conducted continuity tests with DVM and find that R570 & R571(Page126/M2), ref. to Chassis GND. each show the same results. Also that ref.CN13A pin4 where AGND. is generated, shows continuity to one side of R980 and R974 (Page116/L7. So CN13A pin4 is getting somewhere - but not far enough. But CN13A pin4 also goes to that sextuplet of resistors at P114/K5 as RET_GND and I get a beep on all 6 (one side only) but just above that sextuplet of resistors RET_GND branches off to CN115 pin1-2 (and here is where I think there is a break in the conductor) then to Page112/K8 - CP115pin12-13 - Page129/H3 is now CN2pin12-13 (DACRTGND) - Page126/M2 - which is where we came in at R570 & R571. But we've lost continuity with CN13A pin4 now. If you've followed this through to here, "Well Done!" I just simply cannot reason what I'm seeing - But I will!!. Very confusing. Sorry. Michael Studio1 UK 16:45BST 08-06-2018