Denon PMA 1060. Somethings really wrong

Hi! I just bought a Denon PMA 1060 in great condition.
Except one thing, its doesnt work.

When i bought it he said that he and his girl hade been
on vacation and it had been som thunder during the weekend.

So he went to the repairshop and they taught is was
a fuse that blown during a discharge.

I Found a fuse (placed near the on-off switch) that was
blown. So i replaced it.

Turned the Amp ON and BANG! Something broke.
(but the fuse is OK, maybe because i used another
type used more in cars, dont know, stupid me!)

A piece on one of the outputs had been blown away :S
(the one with the yellow wire on the downside of the
circuit board. (isnt it strange with a wire?? maybe it has
been repaired before, dont know)

One of the Caps also blown. (the brown one between the two
biasing pots) It came some stuff out of the cap, hard to see
on the picture.

And before i got the power cord out it starded glowing somewhere didnt have time to see exactly what part.

But i found that a GREEN ;) transistor is in very bad shape.
Nearly shattered in two. Hard to see but its the same picture
as the broken CAP.

The other channel seemes to be OK. I cant see any other damages, sure there is taught. The amp goes in protection i think, red light.


Now to the questions, can this be the result of a discharge
during thunder??

What should i check for? Is it some basic checklist to do?
Check all the outputs, and drivers.. I know.

But do i have to desolder ALL the transistors on the board
and check them, a very time consuming thing to do.

I dont think proffiesionals have the time to do that, but some people claim that its the only way to be sure.

Anmyone have schematic for the Amp?

Im greatfull for all the help i can get =)
 

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silversweden said:
ive been doing some measuring. Conlusion.
For the left channel all the outputs read
0.5 volts 58 volts 0 volts.


But for the other channel many of the pins
have 58 volts, how come?


That indicates something is wrong with the output stage of that channel, bad transistors that have become shorted is the most likely scenario.

That fuse you put in, was the same value as the original, was it? Putting in a higher rated fuse is a complete no-no, something you NEVER want to do.

Other than just the output transistors, some other parts will need checking such as the driver stage, which may or may not have been damaged also.

Start by checking the output transistors one by one (you will probably have to remove them to do this) and replace as necessary. Then move on to checking other things, BEFORE powering up.
 

silversweden

Member
2007-10-10 10:23 pm
im stuck :S

After a couple of hours measuring i got this far.

www.itxpress.se/2434.jpg
komponents marked with yellow was broken.
and marked with green are tested OK.

A strange thing is still after replacing what i found broken.
On the Output pins (i just removed them for now until i
sorted out the problem, have new ones waiting)

Something is really crazy here. Full schematic here.
www.itxpress.se/1060.pdf

TR523
p1 55 (for other channel 0.5V)
p2 58
p3 55

TR527
p1 55 (for other channel 0.5V)
p2 58
p3 55

TR529
p1 55 (for other channel 0.5V)
p2 -58
p3 0.0 (THE 0.22 5W RESISTOR OPEN)

TR525
p1 55 (for other channel 0.5V)
p2 -58
p3 55
 
okay, now im getting frustrated!! :S :p

i found a trace on the board that had been burnt of.
i repaired it with a small isolated wire from the two
solderingpoints instead.

And now i have the same readings on the fets that i
have on the other channel!! ;)

About
0.6 58 0 volts. and so on.

I measured several times. Then i solderd the new Outputs
back in place (4 of them).

I replaced the 4A fuse with a 1.6A fuse just in case.


I plugged the amp in, and it went in protection as
usual. Red light, but some relay clicked. Not the speaker
relays. a smaller one on the same board.


I observed the amp for a few seconds, felt like a long time
but maybe 15 seconds. Then i heard some nasty noise :S

Disconnected the amp within a second.


TR519 blowed!!!! And R549 is just a piece of burnt material.
Dont have the strain to investigate if there is anything
else at this moment.

Anyone have an ideo of what the hell is happening??
And why isnt the fuse blowing before anything else :S
 
okay, now im getting frustrated!! :S :p

i found a trace on the board that had been burnt of.
i repaired it with a small isolated wire across the two
solderingpoints instead.

And now i have the same readings on the fets that i
have on the other channel!! ;)

About
0.6 58 0 volts. and so on.

I measured several times. Then i solderd the new Outputs
back in place (4 of them).

I replaced the 4A fuse with a 1.6A fuse just in case.


I plugged the amp in, and it went in protection as
usual. Red light, but some relay clicked. Not the speaker
relays. a smaller one on the same board.
(maybe the bias current is to high??)


I observed the amp for a few seconds, felt like a long time
but maybe 15 seconds. Then i heard some nasty noise :S

Disconnected the amp within a second.


TR519 and 521 blowed!!!! (all outputs are OK)
And R549 is just a piece of burnt material.

Dont have the strain to investigate if there is anything
else at this moment.
(Can this be the cause of to high bias current?? I really dont se why these two transistors would
go upp in smoke)

Anyone have an ideo of what the hell is happening??
And why isnt the fuse blowing before anything else :S
 
MG, okay, but i checked ALL transistors in the P-Amp section.
They are OK, checked All resistors, OK.. Many Caps checked
for shorts, OK.

The small "input fets" is checked, tought idont know
how to check them propertly, but it reads the same value
as for the other channel, and if they should be faulty
it should read as a short?

And why is not the Fuse blowing!? its original fuses.
The drivers went up in smoke so they have to been
fully open. Cant figure out where the input goes in
to the circuit and where it comes from :S

Last time it was a BIG BANG :p not this time.

I have a scope what is the procedure to trace the
fault? It must be somewhere near the pre-amp
section, or maybe before??

Thanks for youre helping=)
 
If you power the amp through a current limiter (100w light bulb wired in series with the AC mains), you may be able to save a few parts.

Did you try turning the bias control to the minimum setting?

Can you measure the voltage across the emitter resistors and across R549 before any damage occurs? Use clip leads. Make the connection with the power off, power up the unit for just long enough to get a reading then quickly switch the unit off.

You stated that the resistor was a piece of burnt material. You should be using flameproof resistors.
 
Nn fact im not certain that i did turn the bias pot all the way
to close. It looks like ihave two pots to turn on, get really confused, are both bias?? :S

But i dont think this was the cause. Because now ive been
doing some transistor testing on the "input cards" and from what
i can say, they seemed to be OK.

After putting everything back except the Driver transistors
i wanted to measure to se what Voltage i had on the Driver.
(the leg that controls the current flow)

But then i heard that nasty sound!!!!
The DRIVERS OF THE OTHER CHANNEL went up in smoke :S
What the......I havent done anything with that channel.

Then i taught that by misstake i swaped some faulty Transistor
on one of the input cards.
Maybe that is the cause. But that doesnt seem to make sense.

Things just gets mor complicated =) Im in tears and took a break now before i break the hole amp ;)

What should i do? This is becoming quite expensive.


I have to buy 2 sets of Drivers.... And i wont place them in the
circuit before i know the cause of this :p

Do you have any tips perry, dont have the guts to do the
measuring you told me :S

I had an idea now to take the Drivers out (they are dead so have to do so anyway) and MEASURE V on the holes(pins).
Maybe that would tell me something :S

...if i measure at the (collector?) first leg och the Driver.
On the solderpad, without the Driver in place.

I should be able to se if i have to high idling voltage on it?

And yes, im not a pro at this ;) as you see... but i will be :)

Thanks
 
Follow Perry's advice and put a light bulb in series with your amplifier. I use that all the time for testing. At the hardware store I picked up a hexagonal electrical box, light socket, some power cord wire, and a female and male plugs. The light bulb is wired in series.

So instead of blowing transistors left and right, the bulb will just glow brightly when something is wrong. Essentially it acts like a current limiter.
 
yes MG, I will do that next time ;)

But i dont have a clue why the other channels Drivers blew :S

Maybe i Really did swap some part on the input card???

Because before i was there investigating i acidentlyleaved
the amp turned on over night, nothing smoked.....
(i had removed all the burnt komponents from the bad channel)
 

e-mos

Member
2004-06-18 1:34 pm
gvarv
hi,

this is a dc coupled amp as many are.. the trouble with dc coupled amps is any fault any where in the amp amplify trough the amp..

you can have i small error in the pre amp and it will f**k up the output transistors.

a good tip is to leave the output transistors out for testing.
that way you don't risk to blow expensive transistors. the circuit should work fine without the output transistors and this gives you some space to measure.

there are voltages on the schematics that are absolute, measure this and find your fault.

remmeber a transistor can be defective despite it is not shorted...
try to measure the Base Emitter voltages across all transistors. if it is not 0.6 to 0.8Volts it's somthing wrong.

also try to disconect the input connector..

ps. if nothing else works try to replace all transistors and diodes...

good luck...

-emesto-
 
thanks for giving me support.
i havent had the strain to work on the amp for a while.
think i start all over again and check components.

strange think is that ALL the transistors checked OK
last time. i will try and replace some coupling capacitors
and some small elyts. And check the zobel and feedback.

Something is really wrong, or maybe its just a small small
thing that i just cant see.