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Denon PMA-900V Troubleshooting

Thanks guys for the responses/explanations. Currently, the parts that I have pulled are as follows:

Transistors
TR517 / 0.001
TR515 / 0.000
TR513 / 0.005
TR511 / 0.000
TR509 / 0.000
TR507 / 0.586

0.22 Ohm Listed Resistors
R567 / OL
R573 / 0.2
R569 / OL
R571 / OL

4.7 Ohm Listed Resistors
R589 / 4.7
R565 / 4.7
R561 / 4.7
R563 / 4.7

New parts said 3-day shipping but we’ll see how that goes. As far as direction for the interim while waiting on the parts to arrive, I’m open to advice/direction on path from here. I could re-solder the 4.7 Ohm resistors in or wait until installing the transistors since they connect to the same solder joint?

I’ve heard that these mid-80s Denon’s had “cold solder joint” issues but I wouldn’t know how to even identify one. While this thing is on my improvised idea of a workbench and opened up, should I be looking for other issues in this while waiting on parts?

Should I be concerned with anything on the power supply capacitors board (ETC9053-2)?…..I really think I’m overthinking this, but I would swear there is the slightest bit of a bulge on C103/C105/C107 compared to C104/C106/C108, but then again, the metal cover plate has a rubber/foam pad that has sandwiched down on top of C104/C106/C108 for the last 35 years, but the left channel / odd numbered ones weren’t pressed down so that my be the reason for the perceived bulging.

I’m just trying to learn here, not really worried about asking a stupid question if it’s something I don’t know. Thanks.
 
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If you must ask you also have to be careful not to damage solder pads and copper tracks.
 
Alright, parts should be arriving today. For steps from here, should I get everything soldered back in and then power on using DBT and hope for a relay click? Should I even try for sound at this point? Further measurements to be taken if no relay click?
 
Beavs said:
Alright, parts should be arriving today. For steps from here, should I get everything soldered back in and then power on using DBT and hope for a relay click? Should I even try for sound at this point? Further measurements to be taken if no relay click?
Click to expand...
Have your meter on the bias test points as you power up to make sure it is in check and not super high.
Then check DC offset and make sure that is in the ballpark as well.
If that all checks out and the relay clicks you can check for sound.
 
If you want fireworks go right ahead and plonk it all in. Otherwise read the messages above about what to do first. Especially mine.
 
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PE9ZZ said:
If you want fireworks go right ahead and plonk it all in. Otherwise read the messages above about what to do first. Especially mine.
Click to expand...
PE9ZZ - I think some things are lost in translation via keyboard. I do not want fireworks obviously as I am literally asking questions for direction on what to do each step of the way in hopes of doing this the correct way and also learning along the way to better understand this when I take on the next sanity project. Avionic and Raccoon1400 have been pretty straightforward and to the point on steps to take/parts to order. It seems that you and Raccoon1400 may have differing approaches on whether or not to have the newly bought power transistors installed yet for the next step, is that correct? If it's an added step to test in between soldering to prevent potential damage I'm entirely fine with the added step. I believe you would recommend the following approach step by step:

1. install the 0.22ohm resistors and TR509 and TR507 transistors
2. then short between the base and emitter pad of one of the not yet installed power transistors (TR511,13,15,17). Also, clarification here as it was not , this would be between the pad for the base of TR511 and the pad for the emitter of TR511, correct? Not base of TR511 and emitter of say TR513.
3. power on with DBT:
- if relay doesn't click, then there are other problems and no risk of damage to the power transistors
- if relay clicks, power down, install power transistors, then follow Raccoon1400's directions for checking bias and DC offset

Do you agree with the steps listed above?
 
I had it mixed up with another post. Getting old, I know... Your summary is correct. B-E pads of TR511 are as good as any (but indeed not between transistors). You will get relay click when both outputs are zero. You should even get sound from headphones. Not from speakers.
 
PE9ZZ said:
I had it mixed up with another post. Getting old, I know... Your summary is correct. B-E pads of TR511 are as good as any (but indeed not between transistors). You will get relay click when both outputs are zero. You should even get sound from headphones. Not from speakers.
Click to expand...

Okay, thanks for the clarification/ confirmation of steps. Parts did not arrive today so hopefully they'll be here tomorrow.

I will update after I get no relay click for further direction.

OR

I will update with bias and DC offset findings if I do get a relay click, and then direction from there.
 
Alright, parts arrived. TR507 and TR509 back in. Resistors, 0.22ohm, back in. 4.7ohm resistors were already back in. Shorted base and emitter pad on TR517.

Hooked up to 100 watt bulb DBT. Hit the power button and light illuminates bright with no dimming and no relay click after about 15 seconds. I shut it down and unplugged, awaiting further direction from here.

One other thing to note, front panel bulbs would illuminate when powering on before I had done any work to it. When testing now, no front panel bulb illumination. Where to go from here?
 
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Huh?!?!? DBT full on without any power transistors in? That means you have a short somewhere else. What about the 6.3AF fuses F1-4? Still full on with those removed? If not lit then install them back one channel at a time. Your remark about front panel lights suggests you introduced a short during the replacement process.
 
So, I'm baffled. I pulled all four 6.3A fuses and then when powering on the DBT quickly dimmed to a faint glow. Replaced each fuse with same result of the DBT quickly dimming to faint glow. Also, front panel lights now working. Everything in place, powered on, DBT to faint glow and 10 seconds in I get a relay click.

I also thought I must have created a short somewhere but all measurements of items I had soldered in came back as they should. Any idea why pulling and reinstalling the fuses changed things?

Next step, install the the power/output transistors and then check bias and DC offset? Or should I hold off based on the odd preliminary results?
 
No idea what happened at your end. Maybe a piece of wire got stuck somewhere and came dislodged after pulling the fuses. You may want to check for something like that first. I never like incidents like that. Makes me very nervous.

Now you've got relay click test whether voltage across R559 is sane and adjustable with VR5. Should be around 1.0 V. Then turn it to its lowest and power off. Wait for the capacitors to discharge (experience!) or help them with a low value power resisor (100R/5 W is perfect). Install the power transistors. Double check your work, test for shorts, check the correct transistors in their respective places, stuff like that. Do one channel first, disable the other (pull its fuses).
 
R559 measures 0.892 V. When adjusting VR5, no difference was observed in voltage across R559.

On the Right channel (good channel)
R560 measures 1.012 V and was easily adjustable with VR6.

Next things to test and/or parts to add to another BOM?
 
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Started taking measurements of resistors immediately around VR5 in the schematic and got the following:

VR5 / 1.96k Ohm (full counterclockwise rotation)
VR5 / 15.2 Ohm (full clockwise rotation)

R513 / 3.6k Ohm
R517 / 3.4k Ohm
R523 / 1.629k Ohm
R547 / 0.983k Ohm

upload_2021-1-21_11-16-19.png
 
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Not sure if testing the resistors in circuit is telling of anything, but I measured the resistance on R559 which was mentioned above and the other 100 Ohm resistors connected to the base of TR507 and TR509:

R559 / OL
R553 / 100 Ohm
R551 / 10.51 MOhm

Probably not telling much, but I don't understand the ins and outs of diagnosing these, learning a lot through this though.
 
R559 OL and yet less than a volt? That ain't right... Or maybe it is because there is less current going through it. Replace. R551 as well. That would explain the low voltage. Check R553 for damage. If discolored like R551 replace as well. Right now the driver stage still is kaput.
 
As far as ordering these parts online, any tips for how to identify what is or isn't a match? The service manual has extremely limited info, basically the ohm rating.
 
0.5 W metal film will work fine in these positions. You can calculate this yourself. P=V²/R, V=2V, 4/100=0.04 W. As long as they are the same size or bigger as the originals you're good.
 
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