Proton D540 Audio output problem

red73b

red73b

New Member
I bought a D540 a few years back. When it arrived, it had been damaged in shipping with the results being sound out of only one channel. I messed around with it, and discovered if I tapped on one of the larger Caps, I got sound out of both channels, and it sounded good as long as I didn't move it. I assumed it was a cracked solder issue with the capacitor. I upgraded a few months later, and put the Proton away. I am thinking of using the Proton for a second 2 channel system. It now has only barely audible sound from one channel ( volume all the way up) The relay clicks when the amp is turned on, and I have DeOxit'ed all the switches on the front panel. Is it possible to have a dirty relay, and it still clicks on? I have also tried different inputs with the same results...Any and all thoughts on possible culprits is greatly appreciated!!!
 
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Cause could be anything. I'd replace the cap you had to tap to get it first working. Could be a dry solder joint or corrode leads.
Symptoms now read as a power supply issue, suggest do a basic health check of the psu and measure voltages, will see if I
can find the service manual
 
Amp can run as seperate PRE or POWER amp using the PRE-OUT/MAIN IN RCA connections at the rear.
Make sure the joining links from PRE-OUT to MAIN-IN are in place, also there may be a coupling switch
in the vacinity so joining links might not be needed if switch is on/set to coupled.

Would be worthwhile to connect an ipod or ixxx to the MAIN-IN at minimum volume and slowly increase the volume.
This would test the power amp.

Suspect you have a power supply issue that's affecting the preamp opamps IC501, 2
 
measure dc voltage at the jumpers highlighted they should be about +20Vdc and -20Vdc, black probe connected
to chassis/ground
upload_2019-2-28_16-7-51.png
 
red73b said:
I bought a D540 a few years back. When it arrived, it had been damaged in shipping with the results being sound out of only one channel. I messed around with it, and discovered if I tapped on one of the larger Caps, I got sound out of both channels, and it sounded good as long as I didn't move it. I assumed it was a cracked solder issue with the capacitor. I upgraded a few months later, and put the Proton away. I am thinking of using the Proton for a second 2 channel system. It now has only barely audible sound from one channel ( volume all the way up) The relay clicks when the amp is turned on, and I have DeOxit'ed all the switches on the front panel. Is it possible to have a dirty relay, and it still clicks on? I have also tried different inputs with the same results...Any and all thoughts on possible culprits is greatly appreciated!!!
Click to expand...
Like its cousin NAD, I'm guessing there's some heat issues. Touch up all solder joints in hot areas and replace any caps that have heat damage (or all of them).
 
red73b said:
.... I messed around with it, and discovered if I tapped on one of the larger Caps, I got sound out of both channels ....
Click to expand...
That's clearly the first thing to address. Which "larger cap" was it?

As mbz suggests, reflow the solder joint. If that doesn't fix it, replace the cap.

Try to isolate which section alone (if either) has the problem: pre-amp or power amp.

ie, run the power amp alone, if you get full volume out of it, the problem is in the pre-amp section. And/or run the pre-amp alone, if you get full volume out of it, the problem is in the power amp section.

Once you've narrowed it down, there's less to troubleshoot.

Make sure the "ACC" and "Bridging" switches are OFF

Get the service manual w/schematics: https://www.hifiengine.com/manual_library/proton/d540.shtml
 
I still have a D940 I had bought new (not D540) and the one issue that developed with age was the input selector that would always have to be fussed with in order to get both channels to play.
 
mbz said:
Amp can run as seperate PRE or POWER amp using the PRE-OUT/MAIN IN RCA connections at the rear.
Make sure the joining links from PRE-OUT to MAIN-IN are in place, also there may be a coupling switch
in the vacinity so joining links might not be needed if switch is on/set to coupled.

Would be worthwhile to connect an ipod or ixxx to the MAIN-IN at minimum volume and slowly increase the volume.
This would test the power amp.

Suspect you have a power supply issue that's affecting the preamp opamps IC501, 2
Click to expand...
mbz, Thanks for all your suggestions, especially the one regarding the jumpers for the Pre-Out to Mains. I totally spaced the fact that with this unit they have to be in place. Sure enough, they weren't. Found them and put them in, and had full sound on the both channels this morning, although the right channel had some distortion. This evening I powered it up again and only had sound on the right channel, still with some distortion. I will be investigating this further in the days to come. Thanks again for your input!
 
as above, check solder joints, switches probably need a clean, check the bias as a general health check.
 
red73b said:
I finally got around to measuring dc voltage: +21.6Vdc and -21.5Vdc
Click to expand...
Regulated power supply for opamps etc... is good.

Did you followup on that cap you tapped, ie, replace or ...
Also, do you have a IPOD/iphone/Ixxx that you can plug into the main in RCA's, the idea is to run the amp as a power amp
and see if the problem remains.
 
The source selector switches on the D540 are the worst part of the design. They are very hard to clean, impossible to relubricate once you do, and almost guaranteed to need regular cleaning in the future. Spray and work them. Repeat.

A nice amp otherwise and I used mine for over twenty years, but I sure don't miss those switches!
 
mbz said:
Regulated power supply for opamps etc... is good.

Did you followup on that cap you tapped, ie, replace or ...
Also, do you have a IPOD/iphone/Ixxx that you can plug into the main in RCA's, the idea is to run the amp as a power amp
and see if the problem remains.
Click to expand...
I hooked up my iPod to the main in . Got sound from both channels, however the left channel had some distortion. Also, the balance function control had no effect. I assume that is a preamp function, which was overridden by the ipod being used. Thanks again for any and all input!
,
 
Preamp has one opamp and 2 BC transistors per channel.
Most probably an issue with dirty switches. Try connecting source to outher inputs TUNER, DAD, TAPE 1,,,
Also maybe select then unselect the problematic input maybe 20 times, does the sound ever re-appear?
 
mbz said:
Preamp has one opamp and 2 BC transistors per channel.
Most probably an issue with dirty switches. Try connecting source to outher inputs TUNER, DAD, TAPE 1,,,
Also maybe select then unselect the problematic input maybe 20 times, does the sound ever re-appear?
Click to expand...
I tried different inputs , selected then I selected inputs. No change. I then tapped on the large left capacitor a few times and after a few pops through the left speaker...clear sound. There is the occasional pop in the left channel. I presume it is either a cracked solder joint or the capacitor itself? I have examined the underside of the board and I don’t see evidence of a breeches solder. Thanks again for the guidance!
 
Replace the cap, possibly corroded leeds. Let us know what cap number it is Cxxx, also the uf and voltage.
 
red73b said:
It is a C901, 10000uf 80v.
Click to expand...
Afraid you were going to say something like that.
C901 (10000uf/80V) is part of the unregulated power supply, it feeds the "DPD" (google says dynamic power on demand)
circuit positive rail. It is used for both L&R power amp channels. Clearly it's misbehaving, suggest replacing both C901, 902
and go from there.
 
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