Denon AVR-1912 E2/EA

[Michael Studio1]

Michael, If I remember correctly, your problem was the 7v supply to ic801 was only 3.5v.

Either something downstream of D800 is overloading the supply, or the ps is unable to deliver the required current.
There are several approaches to finding the culprit, I like to use an isolation method to finding things but discretion should be used that it won't cause component damage.

You could use an external supply to inject the 7v into just that section to see if that gets pulled down also. Which would prove the ps side is ok.

Many ways to skin a cat.

I'm signing off now to have a cold one.

Regards, John

Perfectly correct., John, Thank you for your comment. Much appreciated. it was indeed the +7V. not arriving at pin80 of the IC801. If those 1N4007's are OK and don't need replacing (bang goes another few GBP), looking at the Cct Diag. (page 114) and comparing it to the -8V. which does arrive at its pin 52 of the IC801 as -7V., the circuitry is much the same. This is indeed a 'puzzler'. I shall obviously have to don my wizard's steeple and go into a corner and think . . . . In the meantime enjoy your 'cold-one' could be an ice cream or a shower!. Best wishes,
Michael Studio1 UK.19:30 GMT

 

[Michael Studio1]

When the consignment of 1N4007's arrives I shall replace D800 just to see what happens! Michael Studio1 UK 19:35 (a good year that - when I was born!) GMT

 

[Tha fios agaibh]

There is the possibility that pin 8 of op amp IC800:B (p114) has internally shorted.
I'd try removing it and temporarily power up to check if your +7v is restored.
Also make sure you check caps C823 and C807 with your esr meter.

 

[Michael Studio1]

There is the possibility that pin 8 of op amp IC800:B (p114) has internally shorted.
I'd try removing it and temporarily power up to check if your +7v is restored.
Also make sure you check caps C823 and C807 with your esr meter.

Thanks, John. That's a very good notion. To remove it I have an 858D (such as Dave Jones was pulling apart a few months back) so it'll be good to give it a whirl. I'll also check those 2 Caps. Family itching to go out shopping - so I'll do this when I get back - and post the results.
Michael Studio1 UK 09:08GMT

 

[Michael Studio1]

Hello, John et al - I haven't got round to the IC800_B but have results on ESR of the two Caps.
C823 = 116.8μF and ESR = 57Ω. Parts List (page 185) shows C823 = 10μF/50V. (as on the Capacitor)
Next cap: I'm sure you meant C808 (not C807) -
C808 = 116.8μF and ESR = 54Ω. Parts List shows C808 = 100μF/16V. (which is on the Capacitor)
So C823 is far from specs. But would this cause that drop in V.? Before I change this cap. I will hope for a comment and not remove the Op.Amp. Michael Studio1. 18:26GMT.

 

[Michael Studio1]

Just 8 mins later the ESR meter reads C823 = 117μF and ESR = 0.54Ω. This is one radical Cap! Michael Studio1 18:36GMT

 

[Michael Studio1]

So I changed C823 to a new 10μF 50V., re-assembled the PCB 'cage' and powered up . . . . No change! The two Signal Tones 700cps and 500cps are getting no further than the input to IC801. Time to call a halt. Next time I shall remove IC800 and see if the voltage re-establishes as +7V. at IC801 pin 80. Michael Studio1 UK 23:07GMT

 

[Michael Studio1]

Having removed and replaced C823 I have applied the Peak Atlas ESR70 to the original C823 and the result is: "Open Circuit or Low Capacitance" so the change was justified. Michael Studio1 UK 23:29GMT

 

[Michael Studio1]

Later: Sunday. Looking at the AUDIO_VIDEO PCB. IN THE Denon AVR-1912 E2/EA (important to have the Version!) There are many annotations on the Cct.Diags. which refer to 'Options' 'frinstance see page 114 in the Service Manual A/V 1/3 D3 there's an 'OPTION H' arrow pointing to a boxed in area of the Cct.Diag. containing R810 and R811. Interestingly, looking at the area containing the Op.Amp. IC800A and B (HIJ5/6) the entire Cct. is enclosed but has no arrow with OPTION but a statement 'OPEN'. That this area is NOT used in this Version of the 1912 seems likely and is backed up by the Parts List (page 185) where the SEMICONDUCTORS GROUP starts with IC801. Here there is no mention of IC800. We are looking for an 8 pin IC. There are two that I can see - one is physically placed between two Caps - C932 & C1021. The other is placed between C975 & C974. On each IC there is engraved '7628' & '1097' According to the Parts List these appear to be: IC821 and IC823. This seems to be getting more like an electronic 'who dunnit' exercise. So - who dunnit? Anyone? Michael Studio1 UK 15:15GMT

 

[Michael Studio1]

Monday. Looking at the AV PCB now I notice there is no IC800. There is a place for it but the component itself is absent - only the markings etched on the PCB show where it would be - indeed it is physically absent from the point diagonally between C823 (which I replaced yesterday) and C825. The culprit robbing me of 4V. has yet to be found!! Michael Studio1 UK 12:07GMT

 

[Michael Studio1]

Another thing I just noticed: Service Manual Page 168 & 169 the IC801 pinout is NOT as per page 114. For example Pin 80 on page 114 is AVCC on page 168 it is INR11/RECR5. And the positions of the pin numbers is totally different. This is all Very Confusing. Michael Studio1 UK 15:33GMT

 

[Tha fios agaibh]

Yes, I thought I noticed some pinout discrepancies on ic801. I didn't say anything because I thought I had the wrong page.
Regardless, you need to sniff out anything downstream of D800 and see what is overloading your 7v rail. Have you tried isolating some of the loads on that node?

For example, pull one lead of R871 and see if voltage comes up.

Better yet, pull the cathode side of D800 and put your meter inline with it to measure the current being drawn.
Like I said, there's either an overload or the ps is the problem.

 

[Michael Studio1]

Yes, I thought I noticed some pinout discrepancies on ic801. I didn't say anything because I thought I had the wrong page.
Regardless, you need to sniff out anything downstream of D800 and see what is overloading your 7v rail. Have you tried isolating some of the loads on that node?

For example, pull one lead of R871 and see if voltage comes up.

Better yet, pull the cathode side of D800 and put your meter inline with it to measure the current being drawn.
Like I said, there's either an overload or the ps is the problem.

Thanks, John, your comment is just what I need to allay the flagging spirits!The 1N4007 consignment arrived and so the D800 has now been changed. But there has been yet another inexplicable test result. The A+8V and -7V. rails have REVERSED!! What was Negative is now Positive and the reverse likewise. I shall change D800 back to the original diode and see if things normalise. Having half done that I shall measure the current at the Cathode before completing the soldering. I did make sure I had put the replacement Diode in the correct way (not that a reversal of one Diode would bring about this extra-ordinary result) - in fact although the Cct.Diag. shows them side by side with Anode of one next to the Cathode of the other, in reality they are installed Cathode by Cathode and Anode by Anode - the routing of the circuitry must make the reversal. I will also pull one side of R871 (if this is possible - it may be an SM component. Michael Studio1 UK 20:44

 

[Michael Studio1]

I fear I have done damage to the PCB in removing D800 again. The foil is very fragile on the surface of this board - as I found on HDMI_PCB (page 126 K3) when C811 broke away from the PCB and I had to replace it by finding the next in-line component and soldering to it. Here the same has occurred with D800 and I must solder one tail to the next in-line component. But I feel I must not try the Current Test you suggest for fear of further damage. YET I am the culprit of the reverse A+ and A- polarity for I discovered to my horror that I had soldered the new D800 backwards, causing that reversal. So, back to the soldering iron and taking greater care! Michael Studio1 UK 21:28GMT

 

[bushtech]

Btdt Michael. You live and learn.

 

[Michael Studio1]

I have restored the Diodes to their correct position, powered up (and it stays on) but the two rails still have reversed polarity. The repair was successful though . . . Ha-ha! Michael Studio1 UK 21:58GMT

 

[Michael Studio1]

Btdt Michael. You live and learn.

I am somewhat lacking in spirit over this right now. What does: Btdt stand for? (you can tell I don't 'tweet'!) Michael Studio1 UK 21:59GMT

 

[Michael Studio1]

Found it! 'Been There Done That! Yes but you came out the other side OK? Michael Studio1 UK 22:02GMT

 

[bushtech]

Hang in there Michael, you will succeed with the help of the hugely knowledgable guys helping you. Just be methodical and keep copious notes of the results of your actions.

Regarding the track lifting, maybe up the temperature of your soldering iron and do put some rosin and extra solder on the solder point you are working on

 

[Tha fios agaibh]

Ahhh, (pulling out my hair)
Here's hoping the reversed polarity didn't make toast of that IC.
Everyone makes a few mistakes, but remember, just one screw up can wreak irrevocable damage.

I don't like that the diagram doesn't match reality. One, IC801 pinout doesn't match, Two, diode layout don't match. What else? The only thing worse than not having a print is having an incorrect one. It may be wise to make your own sketch based on what you physically see and then verify that it jibes with the pdf drawing that you have.

Ahhhh, (more hair). Before you soldered the tail to the next component, you could have just touched your meter probes to get a current reading.

You need to find a way of isolating the fault or we're all just pissing in the wind.