Denon AVR-1912 E2/EA loss of Left Audio

[Studio1@29]

Continuing the test tone probing of VAUXL. See: Audio  Video  B'D  page 103. With the AVR re-assembled on the bench, Different signal tones injected into VAUXL&R  the results were: R Channel only at Speaker Terminal. Examination of foil side of Audio Video B'D, just 33mm from the front edge are two solder test points. One is for A/D_L and the other for A/D_R. I found continuity between A/D_R test point and CN115 pin 15. There was no continuity between A/D_L test point and CN115 pin 17. Therefore I soldered in a Jumper between these two points of A/D_L. The test tone for the VAUXL now gets as far as IC30 - the AD converter (as does the test tone for the VAUXR)
Michael UK   18:08 GMT

[Studio1@29]

Return to problem in Denon AVR-1912 after Christmas and New Year break. The problems have intensified and now signals only get to the HDMI B'D at the Ribbon Cable connector. Also had a problem on the SMPS B'D where the Power Supply to the Primary winding plocketry had come adrift from the pcb. After resoldering the male Primary plug to the pcb  I had to install a strap to the fuse on the foil side to get power to the main Xfmr. I have invested in a FeelTech FY3200S Dual Channel Arbitrary Wave Function Signal Generator to replace my ageing and suspect Audio Signal Generators. The micro CD that came with it was useless as a User Manual, but FeelTech technical Very Rapidly (within an hour) sent me an email with a pdf attachment which gives all one would ever need to know about this Sig.Gen.Unit. M.Zacharius is so right about the possibility of broken solder joints and dodgy pcb's in this Denon AVR-1912. Now I have to trace those two signals and find out why and where they've stopped.   Michael  UK  17:00 gmt.

[Studio1@29]

Hello, mzacharius -
I have tried sending the problems I am experiencing to this Forum but am getting no replies, so I wondered if you, who have been so helpful, could shed some light?
In order to make tests and keep the pcb's connected to preserve their electronic integrity, I have been experimenting soldering 'Tagged Test Tails' to various pins of the various connector blocks so that the conditions at those points can be measured with the AVR powered up.
Currently I seem to have Voltage problems which are causing the Two Test Tones I am injecting into AUXL and AUXR to not get through the AVR.
For example:
(1) the +8V. rail at pin (1) CN101 (see p.110 of Service Manual) should read +8V. But it reads: +10.78V. on my dvm.
(2) the +8V. at pin (14) CN14 (see p.111) should also read +8V. but it reads: +4.589V.
(3) the Positive Power (see p.114), to the IC801: pin (30) should read: +7V. but it reads:  +3.83V. (by Using an Endoscope and a long, sharp, bent probe this is just possible!)
Have you any suggestions to forward this repair, please? Do you approve of my 'Tagged Test Tails' approach? If so, would you suggest attaching 'Test Tails'  to other points for scrutiny? for I am at a stand still!
Really I am a 'Beginner' and realise I should have entered myself as such - but at over 80, where does one 'begin'! (or, indeed, stop?)
Michael  UK

[Zucca]

Studio1@29 please continue to post your analysis, the replies will come for sure. It would be helpful if you could copy-paste some service manual schematics with your finding marked in it.

Imagine a lot of EE looking jumping here, if they see a circuit with some measurement or real pictures they will be more attracted and interested to follow your steps.

For example:

https://www.eevblog.com/forum/repair/hp-34401a-error-612-613-615-617-618-619-621/msg489595/#msg489595

[mzacharias]

Studio1@29 please continue to post your analysis, the replies will come for sure. It would be helpful if you could copy-paste some service manual schematics with your finding marked in it.

Imagine a lot of EE looking jumping here, if they see a circuit with some measurement or real pictures they will be more attracted and interested to follow your steps.

For example:

https://www.eevblog.com/forum/repair/hp-34401a-error-612-613-615-617-618-619-621/msg489595/#msg489595

I replied in this thread.

https://www.eevblog.com/forum/repair/denon-avr-1912-e2ea-8v-wrong!/

[Studio1@29]

So I took a long, hard think about this loss of Left Audio and did more tests in my Lab. And I discovered something very basic. The tone was not getting through to the SPKR for a very good reason - the cable CX4 has two broken conductors in it!! Interestingly this 40 way ribbon cable (pitch is 1mm) is removable at both ends - each end being identical in that they 'crimp' into place and use plastic grab tags which are attached to the printed side. So I totally removed CX4 ribbon, weighed it down on the bench to stop it from skittering about under test, applied the Ohm Meter a Uni-T (UT61E) dvm using sharp probes of thick piano wire which I ground down to a tapered point and attached to the probes by those plastic housed contact connectors which are available in strips of 10 or so on-Line. I discovered that CX4 contacts 5 (A-7V) and 8 (VAUXL) were broken. Hence the loss of the Left Audio. I therefore removed the grab-tag from the HDMI_B'D end where the breaks are (it tore off quite readily) and took my pair of carpet shears and brutally cut off this ribbon at the first crease.  Then I put a thin line of CA glue along the end of the cut-off ribbon (on the printed side - like the other end) and attached the grab-tag, squeezed out and mopped up any excess CA glue, and weighed it down with a heavy hunk of bull-head rail (which I also use as an anvil) It is now gluing in place and should be fully cured by now. The next step is to reveal those 40 contacts in a very delicate way so none of them get nicked or cut. I don't know any realistic way to do this - so if anyone does, I would appreciate a description of the method.
By the way, the Service Manual for the Denon AVR-1912 E2/EA and others, Ver.6 is available to down-load here:

Denon AVR-1912 | Electrical Connector | Insulator (Electricity) - Scribd

Thanks for reading this.  Michael Studio1  UK  19:42GMT

[SoundTech-LG]

Several lengths and flavors available here:

https://www.ebay.com/itm/2Pcs-AWM-20624-80C-60V-VW-1-40-Pin-1-0mm-Pitch-300mm-FFC-Flexible-Flat-Cable/252286710690?hash=item3abd75b3a2:g:TxEAAOSwPc9WwAw6