Panasonic rx-5150 weak audio in right channel

[BMSinc]

Im posting this in hopes that someone may be able to help me troubleshoot. I also want to bring context to my issue and a previous discussion on this forum that unfortunately didn't end in a "fix." the thread can be seen at this forum post linked below. aside from the squealing - this post summarizes my exact issue. for the most part, the audio i hear sounds clean, but just extremely low in the right channel. using line out on the back - both channels have equal audio signal. I'm hoping someone sees this and might be able to help me out.

previous post - https://www.boomboxery.com/forum/threads/new-owner-of-rx5150-left-channel-very-weak.28052/

Picked up a Panasonic RX-5150 with a very weak right channel. Left channel is strong and clear. Right channel is maybe 10% volume.

What I found / fixed already:

• Unit originally would only play properly when the record mute switch was depressed. (fixed by addressing record switch)
• Record mute slider was stuck. Cleaned it with DeoxIT and worked it back and forth until it moved freely. (restored playback without toggling rec mute)
• Cleaned all pots and switches I could access with DeoxIT 2x:
  • volume
  • balance
  • bass/treble
  • radio/tape switch
  • other accessible controls
• Cleaned and reflowed the balance pot solder points.
• Cleaned headphone jack with ISO and deoxit - looks clean, no bent pins, transmits audio to headphones properly (low right channel signal volume).
• Repaired a cracked LED meter / TPS board by bridging broken traces. TPS seek now works correctly and lights properly, so that board seems functional again.
• Voltage selector on back is set correctly.

Symptoms:

• Right channel is weak on tape
• Right channel is weak on radio
• Right channel is weak through headphones
• Right channel is also weak through the built-in speaker
• Balance control fully to the right does not bring the right channel up to normal
• Loudness button works in terms of changing overall sound, but does not fix the weak channel
• TPS button works, but has no effect on the weak channel issue
• Wiggling / twisting / pushing / pulling the headphone plug causes no change at all

Important test result:

• Line out is perfectly balanced left/right.
• I fed the Panasonic line out into another boombox line in and monitored through record mode, and both channels were equal.
• So the source/preamp side appears okay up to line out.

What seems ruled out:

• Tape head issue
• Source selector/front end issue
• Voltage selector issue
• Speaker itself
• Headphone jack alone
• Cracked LED/TPS board as the main cause
• General dirty control issue, at least from the usual suspects

What seems most likely now:

• Fault after the line-out split
• Right channel power amp/output stage problem
• Bad cap / transistor / resistor in the right output path (although the guy in the post above recapped the whole board and didnt get his weak audio fixed as a result)
• Cracked trace or bad solder joint somewhere in the right channel amp/output section (i would need help identifying where this is)

Complication:

• The solder side of the board is not easy to access and I am trying to avoid disturbing the radio dial string unless absolutely necessary.

Question:
Has anyone here actually fixed this exact weak single-channel problem on an RX-5150?
Since line out is clean on both channels, does this strongly point to the AF power amp/output section on these?
Any known common failure parts for one weak channel on this model?

 

[BMSinc]

Tried to get near the ic6R chip and I’m not sure if those solder joints look suspect or not. Should I try and reflow this?

 

[Tinman]

You can usually spot a cracked joint pretty easily with a magnifying glass.
A lot of times what looks to be cracked really isn't (kind of depends on how good or bad your vision is).
You can also check for cracked joints using a small plastic or wooden dowel and running it over the suspect area's joints listening for any changes.
When I can't find a problem and am getting desperate, it seems like I find a lot of solder joints that look suspect but are actually fine.
Should you reflow the above joints, if it's not a pita for you to do, why not?
It can't hurt (as long as you don't solder two adjoining ones together) and at the very least, it'll rule that out as a potential problem.

 

[XLVII]

Hello, Panasonic fan. I've an RX5100. A small brown wire runs from a post on tuner pcb to negative terminal, right speaker. I forgot to reattach this wire and had problems. Can't recall if it was low volume or no volume.

 

[XLVII]

Here's the wire

 

[BMSinc]

Hello, Panasonic fan. I've an RX5100. A small brown wire runs from a post on tuner pcb to negative terminal, right speaker. I forgot to reattach this wire and had problems. Can't recall if it was low volume or no volume.

Thanks for the reply. I’ll go check today. But I have this issue even when the speakers are not connected to pcb via connector. I’m testing with headphones since the issue is happening before the signal even hits the speakers.

I’ll go check for brown wire connections and make sure they are good.

 

[BMSinc]

Here's the wire

I think we are looking at two different units. Mine doesn’t have a separate board for the tuner. And I also believe my issue is happening well before signal gets to external speakers. I just did a once over and checked all wire connections on the unit and they look ok as far as I can tell.

I’ll keep looking in case anything comes up. Thank you for the breadcrumb

 

[BMSinc]

You can usually spot a cracked joint pretty easily with a magnifying glass.
A lot of times what looks to be cracked really isn't (kind of depends on how good or bad your vision is).
You can also check for cracked joints using a small plastic or wooden dowel and running it over the suspect area's joints listening for any changes.
When I can't find a problem and am getting desperate, it seems like I find a lot of solder joints that look suspect but are actually fine.
Should you reflow the above joints, if it's not a pita for you to do, why not?
It can't hurt (as long as you don't solder two adjoining ones together) and at the very least, it'll rule that out as a potential problem.

Reflowed chip and no change is the weak audio issue

 

[Tinman]

Possibly a broken wiper in the volume (or balance) pot?
Check out this post and the link I left to an older thread of mine.
Click here.

 

[Superduper]

I'd say the odds are better than even that you have either a degraded signal coupling capacitor, resistor, or a blown amplifier.

 

[BMSinc]

Possibly a broken wiper in the volume (or balance) pot?
Check out this post and the link I left to an older thread of mine.
Click here.

I read through those threads. I’m clearly in the presence of a genius. I’m not sure if I have volume pot disassembly and reassembly skills like you have, but I guess you also miss 100% of the shots you don’t take….

You really have me thinking this could be the issue. Did you do any testing with a multimeter to see if the pot was problematic before you yanked it? Is that something you could walk me through?

 

[Tinman]

I don't remember about testing it but I was probably at my wits end and was trying different things to find the problem.
If you can desolder, they're not usually very hard to take apart.
Usually just some tabs to unbend.

 

[Ken]

Check everything in the balance circuit. Sometimes you can have a bad wiper, sometimes it can just be dirty and need a touch of Deoxit and a bit of exercise.

Start with the simple things because if Norm is right you will have to put your big boy panties on.

Thats not necessarily a bad thing, but it can get uncomfortable in the summer…

 

[Ken]

I read through those threads. I’m clearly in the presence of a genius. I’m not sure if I have volume pot disassembly and reassembly skills like you have, but I guess you also miss 100% of the shots you don’t take….

You really have me thinking this could be the issue. Did you do any testing with a multimeter to see if the pot was problematic before you yanked it? Is that something you could walk me through?

Not genius

Experience

I have actually found a tiny hole in some rotary potentiometer packages that will take a drop or two of Deoxit.

I don’t remember the inside of this Box off the top of my head. Is the pot rotary or linear? If it’s linear there is no problem adding cleaner. It’s probably rotary or you would have already solved this, were it the problem.

 

[BMSinc]

Check everything in the balance circuit. Sometimes you can have a bad wiper, sometimes it can just be dirty and need a touch of Deoxit and a bit of exercise.

Start with the simple things because if Norm is right you will have to put your big boy panties on.

Thats not necessarily a bad thing, but it can get uncomfortable in the summer…

I do need to put on my big boy pants - I get it. But also I don’t want to fry something when it could be avoidable with experience that I don’t yet have. For example. My first cassette player got a spritz of deoxit on the motor and capstan and that was a MISTAKE. So yea…I’m a bit weary of taking apart my very first pot when there’s very little to no chance that I can just order a 1:1 replacement and pop it back in. Speaking of which. Any recs on suitable pot replacements for this unit? Both volume and balance? I tried to find on eBay and wasn’t successful.

I WANT to do it but I’m just pretty conscious of where my skillsets and experience get a bit thin.

That being said. Someone on stereo to go was kind enough to highlight some spots in the wiring diagram that may be of interest and the two caps directly responsible for powering the channels. So I’m gonna start there because I can just replace the caps no problem and then if that doesn’t work I can try to disassemble the volume pot and see where that takes me.

I originally wanted to “flip” this boombox and was trying to use it as a test to track how many hours and materials I put into it and then see what I could get for it. But by the time I’m done with this and if I get it working. This is going to be my baby and too close to my Heart to part with. I really want to figure this out.

One question. What’s too much deoxit to spray into pots? I think they’ve gotten roughly 3 spritzes but the balance pot is sealed up pretty good. Has a tiny hole in the front. Hard to tell how much gets in.

 

[Ken]

I do need to put on my big boy pants - I get it. But also I don’t want to fry something when it could be avoidable with experience that I don’t yet have. For example. My first cassette player got a spritz of deoxit on the motor and capstan and that was a MISTAKE. So yea…I’m a bit weary of taking apart my very first pot when there’s very little to no chance that I can just order a 1:1 replacement and pop it back in. Speaking of which. Any recs on suitable pot replacements for this unit? Both volume and balance? I tried to find on eBay and wasn’t successful.

I WANT to do it but I’m just pretty conscious of where my skillsets and experience get a bit thin.

That being said. Someone on stereo to go was kind enough to highlight some spots in the wiring diagram that may be of interest and the two caps directly responsible for powering the channels. So I’m gonna start there because I can just replace the caps no problem and then if that doesn’t work I can try to disassemble the volume pot and see where that takes me.

I originally wanted to “flip” this boombox and was trying to use it as a test to track how many hours and materials I put into it and then see what I could get for it. But by the time I’m done with this and if I get it working. This is going to be my baby and too close to my Heart to part with. I really want to figure this out.

One question. What’s too much deoxit to spray into pots? I think they’ve gotten roughly 3 spritzes but the balance pot is sealed up pretty good. Has a tiny hole in the front. Hard to tell how much gets in.

If you look at Caution’s pics you see that there are actually circuit traces inside the pot he bent the tabs and opened up. Those traces are where the carbon buildup occurs so your guess on the amount of Deoxit is as good as mine. I have had to spray it in at the base of the post, and one tiny squirt filled the pot to overflowing. I shook it to take off the excess (or just blew it out with my original equipment lungs.) The trick is do you have a meter to attach to the leads and measure the pot with? If you measure with a meter BEFORE you get this far it may even tell you that it’s normal operation and not the problem. If you take it apart Deoxit might not cut the carbon buildup, a toothbrush might work, so might a pencil eraser.

You wont be ready for the next problem that will eternally spring from this box unless you get good at repairing it. Most of what we are talking about here are a whole bunch of small operations that add up to a complete repair. A calm patient approach and you wont damage a single thing.

your moment of Boombox Zen

That will be $25 payable to the Old Folks Boombox Home Fund, tax deductible, a 501(c) / Tax Shelter for Ken’s Retirement Investments, Overseas Growth Fund, and Venture/Private Equity Caymen Islands Bank.
FDIC insured

 

[BMSinc]

Got some readings here.
Both of those caps appear to be at 4.3V and holds steady while music playin. Not sure if that matters for this issue.
here’s the pin readings on ic8 in order of pin 1-9
some look like they are reading low based on the wiring diagram/schematic. I don’t know to go from here. Others seem to be in range. I had the fader set to middle when testing. Volume as well.


2.14
0
2.14
6.39
1.51
1.5
7.95
4.41
4.33


I did an ohm reading on the balance pot. My meter was set to 200k ohm for the following readings. It shows 34.6k when I have the probes on both of the outer terminals with the balance in the middle. Twisting the pot to both sides ends on 20.8k for both fully right and left.
next, I place one probe on the left terminal and one in the middle, I twist the knob and the resistance changes gradually - no jumps or shorts - fully left it reads the same 20.8k. Turning the knob all the way right ends up at a 0 reading. I got the same values for touching the probe to the right most and center terminals - just in reverse. Knob fully left 0 - fully right 20.8k


The pot itself says 100k on it in faded black ink. I read that the pot should be reading its printed reading of 100k when both terminals are touching the other points? Is this correct? Are we seeing diminished voltage flow in here?

i tested with the speakers attached and now notice a lot of signal noise coming out the unit when theres no tape playing or with the tape or radio playing and theres definitely crackles and some white noise im noticing now. i didnt have that issue before. i fear im making this worse somehow.