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Denon PMA-900V Troubleshooting

Beavs

Beavs

Active Member
Looking for help here...I have a PMA-900V that I picked up and it powers on but has no relay click and obviously doesn't produce sound (already have a 700V that I absolutely love and is working great). I've found a few other threads discussing work on the Denon PMA-xxV line but looking to walk this one through to completion where other threads may have stopped early.

I have the service manual/schematics and basically started down the path of direction from other threads to test the ouptut transistors connected to the main heat sink. I've attached the service manual and a pic of the measurements I've taken so far. Measurements were taken on diode test with Red to the base and Black to the emitter of each transistor leg (if I need to test differently, glad to do so). Not all transistors are labelled for BCE legs, but I understand them all to be in BCE order going from front to back of the amplifier (front is right side of attached picture).

I did not observe any burnt resistors (however, I noticed that there is some chipping off of jackets of some resistors, not sure if that would indicate something, see resistors above TR515 and TR513 in the image, I believe they are R567 and R569).

Additional pics or measurement of anything in question I am glad to provide/upload at anytime.

I'm a mechanical engineer and wish I had taken the circuits classes I took more seriously way back when...I can read through the circuit schematics and understand concepts of individual parts, but when it comes to understanding the circuit as a whole and what is causing what to go wrong I am way out of my area of expertise here. Soldering-wise, I've generally done caps in speakers but have practiced on some throwaway boards as well.

Thanks in advance to any kind soul willing to help walk me through this!
 

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Based on your measurements the outputs channel on the right of the pdf is shorted.
Need to check other transistors in the channel, low ohm resistors, emitter resistors. You can check low ohm resistors in circut, if the reading is higher than the value of the resistor there is a problem
 
Alright, took some more measurements from other transistors and low ohm resistors generally surrounding the previously measured transistors in the circuit. The resistor measurements listed are generally where the resistance settled at but would generally fall down to the listed number and hover in that range. I'm glad to grab measurements of any specific, or list of specific numbers, just shoot me the reference number from the schematic. Measurements as follows:
Schematic # / measured value (volts on transistor, ohms on resistor)

LEFT CHANNEL (i believe so anyway)
TR503 / 0.628
TR507 / 0.586
TR505 / OL
TR509 / 0.001

4.7 Ohm Listed Resistors
R589 / 2.7
R565 / 1.1
R561 / 4.1
R563 / 4.1

0.22 Ohm Listed Resistors
R569 / 2.6
R567 / OL
R573 / 0.7
R571 / OL

RIGHT CHANNEL
TR504 / 0.629
TR508 / 0.590
TR506 / OL
TR510 / 0.768

4.7 Ohm Listed Resistors
R590 / 5.3
R566 / 5.3
R562 / 5.3
R564 / 5.3

0.22 Ohm Listed Resistors
R570 / 0.7
R568 / 0.7
R574 / 0.7
R572 / 0.7
 
Okay, retested the transistors based on the NPN vs PNP guides provided. I had the base-collector-emitter legs identified, just a matter of switching the leads for the PNP transistor from my previous measurements. I updated the PDF with the pic and labels but then also listed those measurements in the list below, re-tests shown in italics and underlined. The dead channel (left I believe) had no changes in measured values for the PNP transistors on the heat sink. Meter is a Commercial Electric MS8232B, not expensive but not harbor freight cheap, think it was $40 at the Depot. These results make more sense to me as there is consistency between the two channels until you hit TR509.

In regard to avionic's comment about pulling the listed resistors from circuit, I'm glad to do so if/when necessary. I had initially measured all resistors on Ohms and not the AUTO resistance feature and there seemed to be a lot of sway in the readings. I switched to AUTO this time around and the 4.7ohm tested out more consistent...the 0.22ohm resistors though, Left Channel is definitely a mess, Right Channel stayed consistent. I'd like to minimize un-soldering and re-soldering if the part isn't needing replacement...but if it's needed for the troubleshooting part of this I'll do it, I'm just glad to have the help/advice walking me through this. Let me know if I need to pull and re-check.

LEFT CHANNEL (i believe so anyway)
TR517 / 0.001
TR515 / 0.000
TR513 / 0.002
TR511 / 0.000

TR503 / 0.628
TR507 / 0.586
TR505 / 0.626
TR509 / 0.000

4.7 Ohm Listed Resistors
R589 / 2.4
R565 / 0.9
R561 / 3.6
R563 / 3.6

0.22 Ohm Listed Resistors
R569 / 2.6
R567 / OL
R573 / 0.7
R571 / OL

RIGHT CHANNEL
TR518 / 0.485
TR516 / 0.485
TR514 / 0.496
TR512 / 0.496

TR504 / 0.629
TR508 / 0.590
TR506 / 0.637
TR510 / 0.578

4.7 Ohm Listed Resistors
R590 / 4.7
R566 / 4.7
R562 / 4.7
R564 / 4.7

0.22 Ohm Listed Resistors
R570 / 0.7
R568 / 0.7
R574 / 0.7
R572 / 0.7
 

Attachments

Beavs said:
LEFT CHANNEL (i believe so anyway)
TR517 / 0.001
TR515 / 0.000
TR513 / 0.002
TR511 / 0.000
TR509 / 0.000
Click to expand...
One or more of these is bad. They need to be removed from the circuit and retested !
 
Beavs said:
4.7 Ohm Listed Resistors
R589 / 2.4
R565 / 0.9
R561 / 3.6
R563 / 3.6
Click to expand...
These discrepancies may be due to .... this issue.
TR517 / 0.001
TR515 / 0.000
TR513 / 0.002
TR511 / 0.000

Again to positively verify they need to be isolated from the circuit and reverified. There are no short cuts !
 
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Beavs said:
I'd like to minimize un-soldering and re-soldering if the part isn't needing replacement...but if it's needed for the troubleshooting part of this I'll do it, I'm just glad to have the help/advice walking me through this. Let me know if I need to pull and re-check.
Click to expand...
Since it seems the outputs on one channel are bad, you'll definitely have to do some soldering and desoldering. When I find fried outputs I pull and test at least the driver transistors. Would be interesting to know avionic's procedure, I'm sure we've each developed our own method.
When transistors are in circuit measure them with the ohms setting, and when out of circuit diode check can be used for a bit more information.

Just make sure you are able to desolder/solder neatly if you proceed on your own, otherwise the job becomes much more challenging and expensive if you take it to a tech. I've seen too many hackjobs.

With these amps it is also easy to miss damaged resistors. Any low ohm resistors in the bad channel should be checked. Low value resistors are often used as fuses. In circuit with the ohm meter is usually ok.
 
Beavs said:
LEFT CHANNEL (i believe so anyway)
Click to expand...
Denon consistently uses the convention that odd component numbers are L_Ch and even R_Ch. These amps do not have short circuit protection which results in many casualties (including my own PMA-700D).

What I do with these complex amps is remove all power transistors from the blown up channel and short the base and emitter pads from one transistor. Doesn't matter which one. This restores the feedback path (R595/7). Then I power up (DBT!) and if the driver and circuitry before that are OK you should be rewarded with a relay click. In your case TR509 is prolly damaged as well and must be replaced first.
 
Okay, so, no short cuts. I'm going to pull the following, please chime in if there are any in the list below that I should hold off on.

PE9ZZ - I'm unclear on what direction you are advising. It reads as though I would power up with DBT after pulling the transistors out of the circuit...is that right? I think you're meaning to replace any bad transistors after pulling and testing, then DBT but just making sure. Also, shorting the base and emitter pads of any given transistor, is this just to be done prior to testing them out of circuit?

Order of removal will be as follows:

LEFT CHANNEL (i believe so anyway)
TR517 / 0.001
TR515 / 0.000
TR513 / 0.002
TR511 / 0.000
TR509 / 0.000

0.22 Ohm Listed Resistors
R567 / OL
R573 / 0.7
R569 / 2.6
R571 / OL

4.7 Ohm Listed Resistors
R589 / 2.4
R565 / 0.9
R561 / 3.6
R563 / 3.6
 
For the transistors screwed to the heatsink (TR511-TR517), do these need to be pulled off of the heatsink to truly be "out of the circuit"? Some adhesive type of tape holding them down after screw removal. Leads have been pulled and all of them are testing out at same results as before (basically 0.00, not OL) but they are currently still stuck to the heat sink. Let me know and I'll pull and re-test, based on the 0V current test I'm assuming these will have to be replaced anyway since the other channel's transistors tested out fine while in circuit and attached to heat sink.
 
Okay, I pulled all transistors from the heat sink as well as pulled TR509. Similar measurement results as before. I used Diode test, leads for NPN (positive - base, negative - emitter) and PNP (negative - base, positive - emitter). TR509, TR515, TR517 being PNP and TR513, TR511 being NPN. Test measurements:


TR517 / 0.001
TR515 / 0.000
TR513 / 0.005
TR511 / 0.000
TR509 / 0.000
 
Pulled and tested out of circuit:

0.22 Ohm Listed Resistors
R567 / OL
R573 / 0.2 (0.7 measure minus 0.5 lead resistance)
R569 / OL
R571 / OL
 
Pulled and tested out of circuit, 4.7 Ohm resistors seem to be good.

4.7 Ohm Listed Resistors
R589 / 4.7 (5.2 measure minus 0.5 lead resistance)
R565 / 4.7 (5.2 measure minus 0.5 lead resistance)
R561 / 4.7 (5.2 measure minus 0.5 lead resistance)
R563 / 4.7 (5.2 measure minus 0.5 lead resistance)
 
Okay, so far the transitors and 0.22 Ohm resistors are shot, I think the 4.7 Ohm are good. What's next from here? I'll wait to ask questions as to how you understand what to look at/for and why you know to look there at the end of all this...I'll just stick to the you say, I do approach for now to not derail the focus of this.
 
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