Uher Power Port 2 only one channel

[Arbusto67]

Hi everyone, I recently acquired the boombox in the title and I'm trying to repair it because it only sounds from the right channel, the left one makes a very faint sound wich is only audible cranking up the volume. I tried the usual things that come to mind when you face this kind of symptoms, such as deoxidizing pots, cleaning the REC/PLAY bar, cleaning the source switch, but unfortunately to no avail. Tried to search the internet for a service manual, even using the original Samsung P72s model, but was able to find absolutely nothing. All of the components on the amplifier board do not seem to be damaged, burned or something.
Have you guys got an idea that could point me in the right direction? The boombox is nice and I don't want to scrap It...
Thanks a lot in advance.

 

[floyd]

Have you tested it with head phones to see if the problem is present there?.

 

[Arbusto67]

Hi Floyd, not yet actually, it seems like a preamplifier issue since it affects every source (I tested the radio and the aux input, the cassette deck has the usual problems with belts and I didn't replace them yet), but I will check it out. Many thanks for the suggestion.

 

[rivetmaster]

I have a Hitachi TRK 9230 with the same problem. Nothing looks wrong on the boards. I've done the same switch cleaning.

I'd like to know how you get on because it could be a similar fix for me.

I'm thinking about swapping the Amp ICs.

 

[Arbusto67]

Tested with headphones and the same problem, left channel essentially muted. I don't know what else to check, I think I'll have to give up on this thing...

 

[Cpl-Chronic]

If you're good with a soldering iron, you could try to reflow the joints around the amp chip/chips. I had a Citiezen boombox with similar issue. It would work great for about 10 seconds, then the left channel would cut out. I reflowed the solder on the IC connections to the board & viola! It works great now, no issues.

 

[Arbusto67]

Hi Cpl-chronic, I checked the solders of the amplifier chip with a magnifying glass and all of them seem to be Ok, only one looks to be slightly lifted up from the board but I checked the continuity between that one and another point and it tested good. I can solder and I will try and reflow all of that joints to see if something changes, thanks for your suggestion, really appreciated.

 

[Arbusto67]

Tried reflowing the solders of the power amplifier chip and, you guess it? No left channel... I think I need an exorcist!

 

[Arbusto67]

Sooo, I decided to thoroughly clean the source switch, removed it from the board, disassembled it and cleaned the contacts with very fine grit paper (they were dirty but noticed that the areas where the sliding contacts move were essentially clean, so I think that the deoxidizing spray actually did its job), reassembled everything aaand, guess what? No left channel! I think that the only possibility is that one (or more) component on the board is bad or out of specs, but without the service manual or at least a scheme to be able to trace the left channel path it's extremely difficult to spot. I hope that something else will come to my mind...

 

[Arbusto67]

Checked the board another time with a magnifying lens and I seemed to spot a not perfectly looking capacitor, checked It with my chinese ESR meter and it turned out to be out of specs, so I replaced it with a new one, tested the device and the left channel is still essentially missing... I think that this was probably my best bet to repair this thing, now I'm loosing every hope, damn!