Luxman r-115 volume troubles
- Thread starter salperta
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I've been taking some readings on the two gangs of the pot (remembered the word). The difference between the readings increases as I turn the potentiometer, but by percentage the difference decreases. When gang one reads 15kOhm, gang two reads 30kOhm, a difference of 50% (of the larger reading). Whereas when gang one reads 90kOhms, gang two reads 120kOhms, a difference of 25%. This may explain why the problem seems less apparent at higher volumes, a symptom that exists in my amplifier and seems very common with other Luxman r-115s when people have this weak channel issue. I know very little about electronics, so please correct me if what I'm saying here makes no sense, but it seems to make some logical sense to me, at least.
Thanks as always!
S
Thanks as always!
S
Binkman
Lunatic Member
Just to be sure, you prob. did measure correctly.. refer to https://www.wikihow.com/Test-a-Potentiometer. I do assume you deoxed the pots and allowed to dry? any play in the shaft pushing in and out.. casings look okay?
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Hmm, unfortunately I haven't found that playing with the volume knob has any effect, even if temporarily, but thanks for the thought, corbin.
I did indeed measure the pot according to those instructions. If you check out the fourth post on this thread, I did have issues with that volume pot from the beginning. Two of the wipers were bent back, so I did have to open the casing up to bend them into place. I thought that maybe I had it fixed, since other people who had similar issues with their R-115 never mentioned that the volume pot itself was troubled, and bending the wipers back did solve some other initial problems with the receiver. On the other hand, a few of the AK threads regarding this issue don't seem to have got resolved.
Do you think it would be worth my while trying to put a new pot in there to at least see if that resolves the problem? Sadly, they don't make that pot any more (I'm not too concerned about the motorized element, but I couldn't find an equivalent double-ganged pot with a volume tap.). Any suggestions on a way to put in a replacement and see if that solves the problem? Or I am going in the wrong direction here?
Thanks so much!
I did indeed measure the pot according to those instructions. If you check out the fourth post on this thread, I did have issues with that volume pot from the beginning. Two of the wipers were bent back, so I did have to open the casing up to bend them into place. I thought that maybe I had it fixed, since other people who had similar issues with their R-115 never mentioned that the volume pot itself was troubled, and bending the wipers back did solve some other initial problems with the receiver. On the other hand, a few of the AK threads regarding this issue don't seem to have got resolved.
Do you think it would be worth my while trying to put a new pot in there to at least see if that resolves the problem? Sadly, they don't make that pot any more (I'm not too concerned about the motorized element, but I couldn't find an equivalent double-ganged pot with a volume tap.). Any suggestions on a way to put in a replacement and see if that solves the problem? Or I am going in the wrong direction here?
Thanks so much!
This may be the wrong path since your symptoms are different. But I thought my R115 had a volume control issue, it drop on both or one channel, I'd have to spike the volume to bring it back, got worse over time... However, I switched it to preamp duty and it worked fine. It wasn't until I wanted to use the headphone amp section that I decided to look into it. Turned out to be the speaker relay.
Hmm, interesting about the relay. I wonder if that could be it. I never get an issue with a channel dropping, just consistently lower on the right.
But it made me think and I checked the dc offset. Left channel (the good one) is reading a healthy 4mv. Right channel, however, is reading a crazy high 115mv!
Does this help at all with diagnostics?
But it made me think and I checked the dc offset. Left channel (the good one) is reading a healthy 4mv. Right channel, however, is reading a crazy high 115mv!
Does this help at all with diagnostics?
I dont know if this will help you or not..but 2 years after I bought my R-117 I had problems with one channel cutting out. If I did a quick increase of volume a few times it would bring the channel back until the next time I used it. Since it was still under warranty I took it in to have it looked at. The first time they just cleaned the volume pot...they said it then tested fine...it didnt. Took it back in and this is what they found and repaired.
Binkman
Lunatic Member
Since you took the vol. pots apart and they show obvious disparity you could leave it in for now.. but that dc offset needs to be addressed.
-High DC offset is generally associated with matched pairs of transistors like darlington arrays. However, supply voltages to transistors, bad resistor, voltage divider, bad cap or just a transistor worn out.
-I have read a few of these type issues on luxmans cleaned up with resoldering aged joints. I'd pull a magnifier out and examine for same. reflow the drivers and outputs on the main board(s) as heating and cooling can cause solder to age faster than a low heat circuit.
So I'd eliminate that possibility first. You can compare V's from the good board the other, too.
-High DC offset is generally associated with matched pairs of transistors like darlington arrays. However, supply voltages to transistors, bad resistor, voltage divider, bad cap or just a transistor worn out.
-I have read a few of these type issues on luxmans cleaned up with resoldering aged joints. I'd pull a magnifier out and examine for same. reflow the drivers and outputs on the main board(s) as heating and cooling can cause solder to age faster than a low heat circuit.
So I'd eliminate that possibility first. You can compare V's from the good board the other, too.
Hmm, so perhaps there are two different issues: weak channel and DC offset problems. Or perhaps they are the same issue.
I have already reflowed the solder joints on all the main PC board transistors with no change. Should I go through desoldering a leg of each main PC board transistor and check the voltages next?
And are there other transistors I should check on other boards too?
I have been doing a little listening to try to narrow down the symptoms and have noticed the following:
1) Which speaker receives the louder sound changes based on how high the volume is on the Lux. At low volumes, the right channel is weak. If I turn down the source (phone through CD in) and turn up the volume on the Lux, after about half way the left channel becomes the weak channel. I had not noticed this at first because I had never turned the volume up that high. Makes me think the issue is something which effects both channels, not just one.
2) The balance knob isn't really working the way I would think it should. If I turn it fully to the left, it cuts out all of the right channel output, but sound is still coming out of both speakers. What I'm trying to say is that if you have L and R stereo output, when the balance knob is left, only L stereo output is coming out of the speakers, it's just still coming out of both speakers (though less on the right). The reverse is true when I turn it to the right. Does that make sense?
The mystery continues! Sounds like I should focus on DC offset first? And what should I do next in that regard?
Thanks as always, very very appreciative of the help.
Saul
I have already reflowed the solder joints on all the main PC board transistors with no change. Should I go through desoldering a leg of each main PC board transistor and check the voltages next?
And are there other transistors I should check on other boards too?
I have been doing a little listening to try to narrow down the symptoms and have noticed the following:
1) Which speaker receives the louder sound changes based on how high the volume is on the Lux. At low volumes, the right channel is weak. If I turn down the source (phone through CD in) and turn up the volume on the Lux, after about half way the left channel becomes the weak channel. I had not noticed this at first because I had never turned the volume up that high. Makes me think the issue is something which effects both channels, not just one.
2) The balance knob isn't really working the way I would think it should. If I turn it fully to the left, it cuts out all of the right channel output, but sound is still coming out of both speakers. What I'm trying to say is that if you have L and R stereo output, when the balance knob is left, only L stereo output is coming out of the speakers, it's just still coming out of both speakers (though less on the right). The reverse is true when I turn it to the right. Does that make sense?
The mystery continues! Sounds like I should focus on DC offset first? And what should I do next in that regard?
Thanks as always, very very appreciative of the help.
Saul
Binkman
Lunatic Member
Well I'm bit confused myself.. for the variable Vol. issues probably best to address the vol. pots as just too much % of variation as you've tested out of circuit, as long as the replacement transistors are equivalent specs, e.g. hfe, output should perform same. Your bias is in spec.
How much recapping have you done?
I do realize the SM does not have voltage references but you can compare the good side transistor v's one side to the other. Vol. zero, no inputs, speakers, bal. knob center. you're not getting snaps or crackles in output so circuit performance as in dc leakage into the audio path.
How much recapping have you done?
I do realize the SM does not have voltage references but you can compare the good side transistor v's one side to the other. Vol. zero, no inputs, speakers, bal. knob center. you're not getting snaps or crackles in output so circuit performance as in dc leakage into the audio path.
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The last two R-115 that were on my bench both had numerous "bad" solder joints on the (upright) power supply board causing all sorts of anomalies. At least 3 of them were ground traces. From the OP with the bent wipers and "chunk" of carbon missing, there is definitely an issue in the volume pot. I am pretty sure there is a Carver receiver that uses the same motorized volume pot, though I can't remember which model. If you don't care if it is "motorized", replace the pot with the same value and pin out with a non-motorized version that will fit the PC board to retain loudness and CD-Direct function.
Binkman
Lunatic Member
Good points @Skywatcher It all starts in the p.s. and I've read similar aged solder joints issues with lux's.. OP has reflowed the main amp boards. Glad you chimed in.. stick around! 
Good points @Skywatcher It all starts in the p.s. and I've read similar aged solder joints issues with lux's.. OP has reflowed the main amp boards. Glad you chimed in.. stick around!
The solder joint "problems" aren't limited to Luxman. Most all brands from that time period have very similar "notorious" soldering issues. Mostly in areas where thermal cycling occurs. The PS board in this Luxman is one of those areas because of limited air circulation. There is also some glue that needs to be removed as well and the component leads checked for corrosion. The three 1000uf caps were globbed with glue on both of the ones I repaired and had significant corrosion on the surrounding components.
Binkman
Lunatic Member
Well noted many hot and cool fine traces ages solder fast. Then who knows.. some good soldering factory assembler techs.. good quality joints and lot# of solder used, the next off the line.. meh! I always get a strong magnifier out and inspect as you never know what in the box? like an xmas stocking? Candy or coal..
These pups ain't getting any younger, we're seeing stuff now that 10yrs ago probably worked fine or were near new.Ak is kinda like the "Island of lost toys".
Yes, the Island of lost toys indeed!
Thank you @Skywatcher and @Binkman! All of this is so helpful. I was truly surprised to find that bent wiper and the "chunk" or carbon missing-anyone ever seen anything like that? It's hard to imagine how that would happen unless someone had opened it up in the past. Even if it got dropped on its head at some point...
I'm not too concerned with the motorized part of the volume pot. I've been having a very hard time finding any 150k Ohm dual ganged pots out there from any manufacturer (nothing on Mouser or Digikey, eg.), motorized or not. Any leads?
The only one I did find I found thanks to a lead by @milo63. I came across this pot, which is very similar, though the loudness tap is a pin rather than on top. Would it work to just bend it back and solder it to the wire currently soldered to the loudness tap? Otherwise, the only dual-gang pots I could find had 100k or 200k resistance. I've been doing research, but it's still a bit out of my knowledge repertoire understanding how, in this amp, substituting one of those might affect performance.
I will take a very close look at the PS board, with the magnifier, looking for cold solder joints, corrosion, and glue. I'm afraid I'm away from home at the moment, so I will have to get back to you on the outcome of that, but would love to at least get the volume pot ordered and see what kinds of problems that solves.
@Binkman, to answer your question, I haven't done any recapping yet. Probably that's a necessity. What I'm thinking is to take this mystery one step at a time, so I know which things I'm doing are solving which problems. Since the pot is pretty obviously damaged, I'm thinking that is step one. Then I'll take a look at and reflow solder joints on the PS. If there's still volume issues and/or dc offset issues, I'll start measuring transistors values across the main pcbs. Luxman didn't make it easy to do any work on this thing without taking it all apart, even just for measuring. Not to mention that getting to most the back of the main pcbs is nearly impossible without either unsoldering the output transistors or removing them from the heatsink.
Thanks again, y'all. So grateful for your expertise.
Thank you @Skywatcher and @Binkman! All of this is so helpful. I was truly surprised to find that bent wiper and the "chunk" or carbon missing-anyone ever seen anything like that? It's hard to imagine how that would happen unless someone had opened it up in the past. Even if it got dropped on its head at some point...
I'm not too concerned with the motorized part of the volume pot. I've been having a very hard time finding any 150k Ohm dual ganged pots out there from any manufacturer (nothing on Mouser or Digikey, eg.), motorized or not. Any leads?
The only one I did find I found thanks to a lead by @milo63. I came across this pot, which is very similar, though the loudness tap is a pin rather than on top. Would it work to just bend it back and solder it to the wire currently soldered to the loudness tap? Otherwise, the only dual-gang pots I could find had 100k or 200k resistance. I've been doing research, but it's still a bit out of my knowledge repertoire understanding how, in this amp, substituting one of those might affect performance.
I will take a very close look at the PS board, with the magnifier, looking for cold solder joints, corrosion, and glue. I'm afraid I'm away from home at the moment, so I will have to get back to you on the outcome of that, but would love to at least get the volume pot ordered and see what kinds of problems that solves.
@Binkman, to answer your question, I haven't done any recapping yet. Probably that's a necessity. What I'm thinking is to take this mystery one step at a time, so I know which things I'm doing are solving which problems. Since the pot is pretty obviously damaged, I'm thinking that is step one. Then I'll take a look at and reflow solder joints on the PS. If there's still volume issues and/or dc offset issues, I'll start measuring transistors values across the main pcbs. Luxman didn't make it easy to do any work on this thing without taking it all apart, even just for measuring. Not to mention that getting to most the back of the main pcbs is nearly impossible without either unsoldering the output transistors or removing them from the heatsink.
Thanks again, y'all. So grateful for your expertise.
Binkman
Lunatic Member
Actually a time out well spent but don't think too much about it especially driving
You really need to throw in all in one big pot, not the vol. pot. pardon pun. You are getting sound and and no pops or hiss etc.. so that's not an indication of bad transistors. So the Vol pots for equal gain in both channels but over traces and solder points is essential. Probably the ceramics caps are okay.. but electrolytics only have so much life in them on the low voltage rated...so up the v's on those and others below 25v and keep the uf rating.
So take your time and get your brain off it... it really helps. Let us know
bink
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I had a similar situation once with not having the right value pot. Cant you add a resistor to both sides of the pot to effectively change it to the value you need...or doesnt that work with audio?
EDIT: Nevermind...I think that would make the pot range more active at one end of the range or the other...so you may not be able to turn the volume all the way down or up.
EDIT: Nevermind...I think that would make the pot range more active at one end of the range or the other...so you may not be able to turn the volume all the way down or up.
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albertotorre
New Member
[QUOTE = "Binkman, post: 12870818, member: 147925"] Bueno, yo mismo estoy un poco confundido ... por la variable Vol. problemas probablemente mejor para abordar el vol. potenciómetros con demasiado% de variación como los que ha probado fuera del circuito, siempre que los transistores de reemplazo tengan especificaciones equivalentes, por ejemplo, hfe, la salida debería funcionar igual. Tu sesgo está dentro de las especificaciones.
¿Cuánta recapitulación has hecho?
Me doy cuenta de que el SM no tiene referencias de voltaje, pero puede comparar el lado bueno del transistor v de un lado al otro. Vol. cero, sin entradas, altavoces, bal. centro de la perilla. no se producen chasquidos o crepitaciones en la salida, por lo que el rendimiento del circuito es como una fuga de CC en la ruta de audio. [/ QUOTE]
Buen día amigos ..
Les comento mi experiencia: con un r-115, varios problemas (perilla de balance, perilla de bass, botón de tono, soldaduras rotas, falla en el integrado selector de entrada análogo), en fin, un desastre. después de reemplazar las perillas defectuosas ( balance y bass), hacer recap en la tarjeta de control de tono y preamp seguía la falla de canal derecho bajo, se hizo reflow a todas las tarjetas, se reemplazo ci de selección de entrada y se limpiaron y reemplazaron botones push con enclave, solo faltaba el botón de loudness... Y que creen?
Era el maldito botón de loudness, supuse que estaba por separado a lo que era el volume que llega a la etapa de preamp, pero no, es un puente por donde pasa la señal de audio antes de llegar al preamp.
Se limpio y el sonido fue más claro y parejo, debo reemplazarlo pero creo el asunto quedó resuelto, espero sea de su utilidad.
Saludos
¿Cuánta recapitulación has hecho?
Me doy cuenta de que el SM no tiene referencias de voltaje, pero puede comparar el lado bueno del transistor v de un lado al otro. Vol. cero, sin entradas, altavoces, bal. centro de la perilla. no se producen chasquidos o crepitaciones en la salida, por lo que el rendimiento del circuito es como una fuga de CC en la ruta de audio. [/ QUOTE]
Buen día amigos ..
Les comento mi experiencia: con un r-115, varios problemas (perilla de balance, perilla de bass, botón de tono, soldaduras rotas, falla en el integrado selector de entrada análogo), en fin, un desastre. después de reemplazar las perillas defectuosas ( balance y bass), hacer recap en la tarjeta de control de tono y preamp seguía la falla de canal derecho bajo, se hizo reflow a todas las tarjetas, se reemplazo ci de selección de entrada y se limpiaron y reemplazaron botones push con enclave, solo faltaba el botón de loudness... Y que creen?
Era el maldito botón de loudness, supuse que estaba por separado a lo que era el volume que llega a la etapa de preamp, pero no, es un puente por donde pasa la señal de audio antes de llegar al preamp.
Se limpio y el sonido fue más claro y parejo, debo reemplazarlo pero creo el asunto quedó resuelto, espero sea de su utilidad.
Saludos