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 another 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?
Thanks for the bullet points, most of the time people will ask and you have no idea what they've tried. I've got 101 projects going on so I rarely take apart equipment but with the squeal or low volume I've always cleaned the record bar and FUNCTION switch. 90% of the time that works but I have a few pieces here that still squeal including full-size components. Since it has AUX out can you check the DC Offset? I haven't done this yet and I don't think boomboxes are mentioned in this thread but it might help narrow down other issues. https://audiokarma.org/forums/threads/amplifier-distortion-dc-offset-and-you.5634/
I’m not proud of the amount of deoxit I’ve sprayed into the record switch since this was the original offender of the state of the box when I got it. Had to hold down rec mutes switch to get audio. Come to think of it I don’t know if it was balanced. Record switch was stuck in place. I did about 4 rounds of light spraying on that and worked the switch several times until it felt buttery smooth. It appears to work as intended. I believe the record function is servo controlled? I’ll see if anything is up with the function switch but it also seems to work as intended. At any rate. I’ve done as much spraying into this thing than I’m comfortable with. I will look into this dc offset topic and see what is going on since this is a rabbit hole I haven’t been down. I did get some pics of the ic chip. Does this look suspect at all? Should I try and reflow it for posterity sake?
Hello bmsinc, I have had record switches so bad that I had to unsolder them and take it apart and clean and lube and put back in the machine . Also near IC6R there is a cold solder joint in your photo too and yes check the DC offset . This where a dual trace scope comes in handy ! Sincerely Richard
thanks for your comment. The record switch was severely stuck in place when I got the unit but I’ve jiggled it quite a bit and a few deoxit sprays and seems to reliably move now with no resistance or crunchiness. It does make me wonder how bad it still might be inside. You think this could really be a related to weak single channel audio? I did reflow the ic6R chip this morning and there was no improvement in the decibel level of the right channel (through headphones) I’ll get to the DC offset tomorrow. I’m not sure how this works but I will give it a go and report my findings. Thank You again for trying to help. I’m at my wits end with this unit.
you reminded me of the photo I posted here at S2G ten years ago: I had the same problem with this RX-5500 and had a lot of 'fun' trying to fix it. Here is me using Cold Spray on the mainboard, in an attempt to find the glitch: In the end I had to do it The Hard Way and just traced the signal. It was failed MPX filter which caused the dropouts: Since I was not going to record from the radio (never did and never will), I just removed them:
Thanks for giving me some more breadcrumbs to follow. When you say removed them….you just pulled right off the board and called it a day? or did you have to put something in the terminals to bridge them so signal could pass through? I’ve not heard of an mpx filter module on this particular pcb…
Yes, I removed MPX filters (marked L and R on photos) and bridged the terminals (Yellow wires, last photo). RX-5150 does not have MPX filter as a separate 'chip' but my point was that sometimes failed part is not evident and has to be traced Make sure that you have good Right Channel through Line-Out, download RX-5150 Service Manual (it is free download) and start looking 'downstream' of R132/R232. You have one working Left channel, this makes the search somewhat easier
Hi, I'm attaching a portion of the circuit. Verify that the power measurements are correct at the IC pins... Since the output line is fine (green arrows), the problem could be in preamplifier IC8, which controls the input tone and the output volume and balance, and then powers the power amplifier chips via two electrolytic capacitors... Check if you have any of these defective capacitors with high ESR, or replace them directly... the input and output electrolytic capacitors you see in the diagram will suffice.
This is so helpful. I’m going to see if I can have a go at this tonight and see what I find. Thank you so much. I was trying to get ChatGPT to annotate images just as you have and it’s so wrong and random and not helpful. Sometimes it will pinpoint traces that don’t even exist or it will put a mark in between traces…so bad. It has its moments though. Thank you so Mitch for marking this up for me. I’ll report findings soon. Should I be measuring with my multimeter? I don’t have an oscilloscope. in pun 8 and 9 on ic8 left and right audio by chance?
good news is that I have actually found the caps on the board with the help of your annotated picture. Thank you so much for that. If you can’t tell I simply don’t know how to use a multimeter to check the voltage as I read you shouldn’t be doing this while it’s plugged in because you can short and fry things. So I’m hesitant to just start probing away. I guess my next step is to just pull and replace them. I don’t have any means of measuring the esr levels so I figure it wouldn’t hurt to just put some new caps in there to essentially rule them out as problematic. I’m confident in my abilities to do this once I can figure out the values of them. It’s my understanding you can use higher voltage caps but have to match the other measurement exactly.
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? Are we getting somewhere?
