Hi and Happy Holidays. My best and favorite amplifier is a Denon PMA-737 I bought new in 1985. It still sounds great. However, on all inputs (FM tuner, DAD and Monitor), it has an issue where upon turning the Volume control up from 0, the speaker sound is first heard on the left side, and then gradually, the right side comes up and balances dead center once the Volume control is at the 2-3 position. The same thing happens using Headphones via the headphone input, and with other sets of speakers on both A and B speaker terminals.
I've De-Oxidated the Volume pot and Balance control several times but the issue remains. I've also re-soldered the eight connections that hold the volume potentiometer in place. My expertise stops about there so I'm wondering if any of you could suggest another solution or maybe point to the next possible cause?
Thanks
I've De-Oxidated the Volume pot and Balance control several times but the issue remains. I've also re-soldered the eight connections that hold the volume potentiometer in place. My expertise stops about there so I'm wondering if any of you could suggest another solution or maybe point to the next possible cause?
Thanks
This might sound an odd question but is the problem permanent or does it seem better if you turn it up pretty loud and then back down again? That is just to rule out possible speaker relay contact issues.
Apart from that, what you describe sounds like a classic case of mismatched resistive tracks in the dual gang volume control and replacement would be the only real fix for that. Eight connections to the control suggest either a motorised pot or one with 'loudness tapings'. Motorised and tapings would be ten connections.
Apart from that, what you describe sounds like a classic case of mismatched resistive tracks in the dual gang volume control and replacement would be the only real fix for that. Eight connections to the control suggest either a motorised pot or one with 'loudness tapings'. Motorised and tapings would be ten connections.
No it's permanent. Unfortunately adjusting the volume control way up and back down doesn't have an effect. If I go back to 0, it again favors the left side as it diminishes in volume.
Fair enough. So it is looking like the actual control then... and replacement is the only realistic option for a fix, Mis tracking of dual gang pots is surprisingly common even from new though. The loudness taps are also a real barrier to substituting it with a normal pot (you would lose the loudness function) although I haven't actually searched for any.
You might be able to 'fiddle' the issue a bit by attenuating the level applied to the pot which would then mean you having to turn the control up a bit more to get the desired level. Assuming the amp has plenty of gain that should not be an issue. You would just need a couple of resistors to add in series with the feed to the pot (one for each channel).
Would have to see the circuit to advise better on that though.
You might be able to 'fiddle' the issue a bit by attenuating the level applied to the pot which would then mean you having to turn the control up a bit more to get the desired level. Assuming the amp has plenty of gain that should not be an issue. You would just need a couple of resistors to add in series with the feed to the pot (one for each channel).
Would have to see the circuit to advise better on that though.
Thanks... I'll open it up today and take some pics. It's definitely not motorized, but it is a dual-gang part. Hopefully the potentiometer is replaceable.
(I'll also remove, clean and re-solder the balance control while I've got it opened up)
(I'll also remove, clean and re-solder the balance control while I've got it opened up)
I have had three PMA-737, all with tarnished relay contacts. After replacing all three, the sound was good again...
Desolder, remove and clean all the switch selectors: I had the same problem on an old pma-260 and now it's working fine.
See also here (scroll down)
https://bubblecomposuki.blog.jp/archives/17598589.html
Thanks... Being a novice, can you tell me where the relay contacts are located?
Desolder, remove and clean all the switch selectors: I had the same problem on an old pma-260 and now it's working fine.
Thanks for the link. I tried cleaning the switch connectors as best I could from the top. I'll remove them and see if I have better access underneath.
Thanks for the link. I tried cleaning the switch connectors as best I could from the top. I'll remove them and see if I have better access underneath.
Yes! I just got done de-soldering, cleaning and re-soldering the Volume and Balance pots. I decided to play some music through the unit. At first, the right side was completely dead, BUT when I pushed in the VIDEO button (the connected source) all the way in on the front, it immediately played perfectly! So, I assume you're talking about these right? Remove, clean and re-solder?
So the volume related problem disappeared?
If so then you have the issue of oxidized contacts in the signal selector path.
In addition to the input selector switches (Tape 1/2, Video/Aux etc) you need to clean the Monitor switch - it is the "last man standing" in the signal path and gets very rarely used so bad contacts inside are likely.
I would start from just working each switch tens of times to see if any change happens.
At least in my amp, the volume problem was caused by the input selector (the one with the flat blue link; rec out in your amp). It's possible that the input selector push-buttons are in the same condition and need to be cleaned as well.
That should be the output signal (for recordings) selector and would affect sound in case of e.g. equalizer being connected in one of the tape loops.
Yes!
Last night I was running out of time so with a small jewelers screwdriver, I carefully lifted the plastic backside of each input selector switch (the white ones) and using the extension straw, sprayed the last amount of D5 I had in the crevices. I then worked each switch about 20 times. I played music through each of the inputs and so far, the Denon is working like its old self again.
I can continue to the blue selector switch today but all I have left is CRC Electronics Cleaner or WD40 Contact Cleaner. Ordering more Deoxit will take 5 days, probably due to Christmas orders. Going forward, are any of those usable or would you suggest I wait for more Deoxit to arrive?
Nice pic... Yes, still on the agenda but I need to get a better de-soldering tool. I've been using de-soldering wick and it's very time consuming. I saw a guy on YouTube with some kind of round push-button tool that seemed to work better and faster. Still researching it.
To clean switches once they're opened, would you recommend 91% alcohol, Deoxit or something else?
Thanks
To clean switches once they're opened, would you recommend 91% alcohol, Deoxit or something else?
Thanks
Yes, so far so good thanks. At this point I plan to de-solder, open and clean all the switches. As I said earlier, even a light spray cleaning to the white input selector switches proved that my problem was related to one or more of these.