New owner of RX5150. Left channel very weak.

[Superduper]

I don't appear to have that service manual so I can't comment on the cap mismatch or about the amp chip availability. You'll have to check those yourself. The corrected screech and squeal that was fixed is already indicative that at least one or more of the original caps were failing/failed and fixed by the new ones, but as all original caps are all the same age, you still need to replace the rest. After all, the ones that weren't replaced might be the one that is causing your problem.

As for replacing the amp chip, BEFORE you do that, why not confirm that the amp is the problem and not the low level signal path? To do that, check what amp chip your system uses. Using block diagram or schematic, find the L/R input pins and temporarily bridge them with a jumper. Don't do this "live" with a loose jumper - tack it on with solder and set off. Too many members have taken the live route and ended up toasting something, then coming back looking for help. Ignore at your own peril. Now, if the L preamp signal is lower than normal, bringing the normal level signal from the right to the left should make them play equal. But if still low, and you also get low L audio through the headphones jack, then you may consider the amp chip suspect. If you are unable to decipher what pins are the input pins, look up the Datasheet for that particular amp module. It's almost certainly on google. The Datasheet will give you pin-out identification and also how to determine which pin is #1. Although it is possible to be a bad amp, I still think that is not as likely as a problem in your audio signal path. Or maybe your headphone jack (and ext speaker jack, if it has) needs to be cleaned.

Oh one last thing.... it is easy to rush and mistakenly put the wrong cap in place when replacing. It is easy to look quick and see 10 and think you need a 10uf, but maybe it is a 1uf 10v? In other words, be careful, especially when dealing with the 1, 10, etc. And needless to say, you did observe proper polarity during the replacement right? If all caps look original and not replacement, then you should stick with polarity as installed by orig cap -- the board legends aren't always right. I've seen misprints.

 

[robgmn]

I don't appear to have that service manual so I can't comment on the cap mismatch or about the amp chip availability. You'll have to check those yourself. The corrected screech and squeal that was fixed is already indicative that at least one or more of the original caps were failing/failed and fixed by the new ones, but as all original caps are all the same age, you still need to replace the rest. After all, the ones that weren't replaced might be the one that is causing your problem.

As for replacing the amp chip, BEFORE you do that, why not confirm that the amp is the problem and not the low level signal path? To do that, check what amp chip your system uses. Using block diagram or schematic, find the L/R input pins and temporarily bridge them with a jumper. Don't do this "live" with a loose jumper - tack it on with solder and set off. Too many members have taken the live route and ended up toasting something, then coming back looking for help. Ignore at your own peril. Now, if the L preamp signal is lower than normal, bringing the normal level signal from the right to the left should make them play equal. But if still low, and you also get low L audio through the headphones jack, then you may consider the amp chip suspect. If you are unable to decipher what pins are the input pins, look up the Datasheet for that particular amp module. It's almost certainly on google. The Datasheet will give you pin-out identification and also how to determine which pin is #1. Although it is possible to be a bad amp, I still think that is not as likely as a problem in your audio signal path. Or maybe your headphone jack (and ext speaker jack, if it has) needs to be cleaned.

Oh one last thing.... it is easy to rush and mistakenly put the wrong cap in place when replacing. It is easy to look quick and see 10 and think you need a 10uf, but maybe it is a 1uf 10v? In other words, be careful, especially when dealing with the 1, 10, etc. And needless to say, you did observe proper polarity during the replacement right? If all caps look original and not replacement, then you should stick with polarity as installed by orig cap -- the board legends aren't always right. I've seen misprints.

Thank you again for the continued excellent advice!
I'm betting a nickel the cap mismatch can be pinned on the service manual I have. I noticed that it references tuning adjustment for LW/SW/AM/FM; this unit only has AM/FM. I assume there may be slight differences between the radio that has four bands and one that has only two.

Another possibility is that the manual also notes (which I just noticed) that the capacitor parts list is for "Service standard parts" "which may be different from original values".
I replaced on a piece-for-piece basis, working my way across the board instead of looking at a cap value on the list and finding the corresponding hole. I'm guessing that it can't hurt anything to have replaced each piece with an exact match (though almost all of the voltage ratings are higher on the news caps). I assume it's not necessary to go back and swap out the original value for the service value.

I was fastidious in matching polarity of the replacement cap to the original. I checked it on removal, and then made sure it corresponded with the marking on the board as a backup, so I feel very confident there. I'll get my hands on those last seven caps ASAP, get them put in, and see what happens. They're scattered (both physically, and in cap value).
It sure would be a kick in the pants if the unit sprang back to life once they were in!

If not, then I'l try bridging the input. Is the signal that I may be bridging just a simple line-level (such as comes out of a CD player, tape deck, etc), or is it even lower level?
I'm thinking ahead that if the it IS the amp that is the problem (though current evidence says no), could I tap the signal from there and turn the whole shebang into a preamp?
(A ridiculous premise, I know; the tinkerer in me makes me think up stupid stuff sometimes, and then I try to figure out how to see it through. If nothing else, it keeps me thinking, and i usually learn a bunch of new stuff along the way).

 

[Superduper]

Depends on the design, each is different. But it’s probably around line level. If you are thinking of using those for an add on amp, it’s possible but also possible to discover ground loop issues or distortion that is difficult to source.

 

[hopey]

Give a thought to the Volume, Bass, Treble and Balance pots these could be droping the left channel. Also check the MIc input just insert the plug a few times.

 

[robgmn]

OK. Recap is complete. All caps correct, all polarities correct.
All controls (including record bar), and jacks given a DeoxIT treatment. Twice. All jacks have had a plug inserted and removed multiple times.
Low volume continues in left channel, whether through speaker, headphones, or ext. speaker jack.
I checked the line-out on the back of the unit and it is passing signal at equal levels in both channels.

It was stated earlier that there is only one amp chip ("IC5"), but the schematic shows two identical chips (IC5 and IC6) with each wired identically and one driving the left channel (IC5) and one driving the right channel (IC6).
I think the signal comes in at leg #10 on each chip as it seems those are the only ones connected to the rest of the circuit board, while all other legs are connected to each other and ground, or to the speakers/headphone jack/external speaker jacks.

Would those be the two that I bridge to determine if it's an amplifier issue or an issue with the signal going into the amplifier?

 

[Superduper]

Ok, as I said, I don’t have this schematic so I don’t even know what modules your unit is running. I was pretty sure from memory that it’s only a single dual-channel amp but I could be wrong. Before I comment on what pins to bridge, please share the amp chip model you are indicating. Unless you are positive that the service manual is correct for your unit (model suffixes do matter), ideally you should look at your mainboard & identify the amp chip(s). They would be the one with the most substantial heat sink.

 

[robgmn]

The circuit board has two BA532 chips mounted side-by-side, each in its own heatsink.
The following diagram is somewhat
similar to the layout shown on the service manual I pulled from the HiFi Engine website.

If I could insert a picture directly from my computer, I'd post a screen snip of the diagram that's in the service manual.

 

[Superduper]

Ok, so your unit uses the Rohm chips, same as Sanyo M9994. Bridge pins 5 counting from notch or Mark & see if audio is same L/R.

 

[robgmn]

I bridged pins #5 from the notch and the left speaker sprang to life, just as loud as the right. I guess both amps are working!
When I turn the balance full-right, the volume remains the same. When I turn it full-left, it drops off to almost nothing.
Gonna' trace the signal path on the schematic from pin #5 on the left amp and see where it goes.
I assume to another one of the ICs which is a preamp IC(?)

If this goes any deeper, how bad would it be to just leave the bridge in place and run it as a mono box? Stereo separation from speakers 6" apart isn't much of a concern to me (it becomes more of a concern if it's something I can fix easily, chuckle).

 

[Fatdog]

If this goes any deeper, how bad would it be to just leave the bridge in place and run it as a mono box? Stereo separation from speakers 6" apart isn't much of a concern to me (it becomes more of a concern if it's something I can fix easily, chuckle).

You would lose that sweet Ambience mode. Speaking of which, I wonder if a bad Ambience switch is the culprit.

I'm glad to see you are making progress. I think most people would have quit by now.

 

[robgmn]

Fatdog, on 26 May 2018 - 12:56 AM, said:

robgmn, on 25 May 2018 - 10:38 PM, said:
If this goes any deeper, how bad would it be to just leave the bridge in place and run it as a mono box? Stereo separation from speakers 6" apart isn't much of a concern to me (it becomes more of a concern if it's something I can fix easily, chuckle).

You would lose that sweet Ambience mode. Speaking of which, I wonder if a bad Ambience switch is the culprit.

I'm glad to see you are making progress. I think most people would have quit by now.

Ambience switch seems to work as the sound definitely changes when switched from mono to stereo to Ambience. It even changes when switched to ambience with the amp inputs bridged.
I know that pins #5 from the amp go to pins # 8 and 9 on another IC chip ("IC8", which is a RVIBA6133, which I assume means "BA6133").
If that's the preamp chip and the level is too low out of that, then my head may have gone under the water for the third time...

 

[Superduper]

Unless someone else here has a service manual to follow along and trace the signal path for you to suggest components along the path that may be the problem, I would only be guessing, I don't even know what components this system employs. I can tell you that BA6133 is not the preamp, nor does the system necessarily use an integrated preamp "chip". The preamp on this model could simply be made up of discrete components. The BA6133 is the "ambience" chip.

You mentioned that when the balance control is moved to one side, the volume stays the same? However when moved to the opposite side, the volume drops to nothing? This symptom might be telling. The pot and appurtenant circuitry might warrant looking into.

 

[robgmn]

Unless someone else here has a service manual to follow along and trace the signal path for you to suggest components along the path that may be the problem, I would only be guessing, I don't even know what components this system employs. I can tell you that BA6133 is not the preamp, nor does the system necessarily use an integrated preamp "chip". The preamp on this model could simply be made up of discrete components. The BA6133 is the "ambience" chip.

You mentioned that when the balance control is moved to one side, the volume stays the same? However when moved to the opposite side, the volume drops to nothing? This symptom might be telling. The pot and appurtenant circuitry might warrant looking into.

You've been very helpful and I really appreciate it!
I have that manual from HiFiEngine, but I think I may be approaching repair territory that I don't want to get into (having to remove the tuning string and dial to access solder joints, etc).
It'd be a kick to have the box functioning 100% (believe it or not, the tape deck still works fine), but I'm concerned (afraid, really) that if i venture much further, I'm going to screw something up that I can't fix..

So, I think I'm going to button it up with the mono bridge in place and leave it switched to "mono", and just enjoy it for what it is.
Of course now that I've found one, I'm going to be looking for another one that's the same or better at as a good a price as this one...

 

[sunshine_ax]

Yep, screeching / squealing is usually caused by a dirty record bar. Here is a link to what you are looking for (note the following link is a different boombox, but the record bar will still be similar):

https://boomboxery.com/forum/index.php?app=core&module=attach&section=attach&attach_rel_module=post&attach_id=35118

Spray some contact cleaner in there and work the mechanism by hand a few times. It should help clear things up.

That you SO MUCH for that link. I was confused as to what this record bar was. I'm going to clean this on my other boombox too to see if this helps. I appreciate all of the help and info here.