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Old 18th February 2020, 04:01 PM   #11
paczeltf is offline paczeltf  Hungary
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Quote:
Originally Posted by FACT75 View Post
(...)
I have a multimeter but I donít really know how to use it.
I plan to post pictures.

Help wanted!
Elekit usually provides some reference voltages, the 8500 manual does not have a separate table but if you look at the schematic closely, you will see some values. The amp is fairly simple, especially the line level part, which I assume you tested. The power supply is shared so if one channel works then there should not be any issue there.

Here is what I would measure with a multimeter:
1) DC voltage on R39 and R40 cathode resistors (2.5V)
2) DC voltage on R49 and R50 cathode resistors (60V)

Note that you may need to change the voltage range for these measurements if the multimeter does not do that automatically.

If these are all within 10% then the muting relay is the next potential candidate.

While the unit is on and power amp is being disconnected, measure the DC voltage first on the two RCA outputs (should be <1mV) then the resistance between the same points (RCA inner and outer pins). If the resistance is zero on the silent channel then the muting relay needs to be replaced.
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Old 18th February 2020, 04:56 PM   #12
Badchile is offline Badchile  United States
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The 90 degree right angle solder connections are difficult to make well - it is hard to evenly heat the two pads, and on my TU-8200 build I had a couple low quality joints that needed to be redone after I put everything together. Aside from the trouble shooting tips above, check the 90 degree solder joints and reflow if necessary.
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Old 19th February 2020, 03:54 AM   #13
Steve Morley is offline Steve Morley  Canada
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Fact75,
Have you resolved your issues? Are you in Sweden? You're flying the Swedish flag. There's another fellow flying the Swedish flag that posts on the Tubes/Valves forum. Look, I know Sweden isn't Luxembourg but it's not Canada either. Leave a message on tubes/valves looking for local help. You might luck out and find somebody relatively close.

Steve
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Old 19th February 2020, 03:59 AM   #14
Steve Morley is offline Steve Morley  Canada
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His handle is OldHector and he lives in Taby, Sweden. Sent him a private message if you wish.

Steve
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Old 19th February 2020, 08:27 AM   #15
FACT75 is offline FACT75  Sweden
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Thanks all,
This forum is truly great! I'm glad for all the response but sadly I don't have much time to spend on my little project so please don't be alarmed if I don't respond directly.

I will re-solder the 90 degree right angle connections. Thanks BadChile.

Yes, I do live in Sweden. I'm new to this forum so I don't know anybody here yet. Thanks for the tip about OldHector.

I'm also very new to diy electronics and measuring with the multimeter. I'm not very keen on "While the unit is on ... measure the DC voltage ...". Is that safe? I have too little experience to poke around in a plugged in amplifier and I have a lot of respect for 230V.

Steve, I re-soldered the volume control and soldered a wire between the two middle pins. I still have sound in just left channel so i guess the Bug is after and not before the volume control.

IMG_1965.jpg

So, I guess the problem is somewhere here:

Schematics_V2.jpg
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Old 19th February 2020, 11:31 AM   #16
paczeltf is offline paczeltf  Hungary
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Do the voltage measurements as I explained above. If you are not familiar with your multimeter then send a photo of its front panel.
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Old 19th February 2020, 11:59 AM   #17
adason is offline adason  United States
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fact75, it seems to me on the last picture, the one with red shorting wire, that on the bottom right you have at least two blobs of solder which could be shorting someting
clean them and see

just unrelated, what happened to me few times already...when i finished preamp, or active crossover, i did not have sound in one channel
all voltages measured fine between left and right, after countless hours of debuging i found one tiny wire from the shielding still attached to the live signal wire...there is always one tiny almost invisible ground wire hanging on the plastic
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Old 19th February 2020, 12:39 PM   #18
FACT75 is offline FACT75  Sweden
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Quote:
Originally Posted by paczeltf View Post
Do the voltage measurements as I explained above. If you are not familiar with your multimeter then send a photo of its front panel.
I have this multimeter:
UNI-T UT125C

Still not convinced that I will survive.
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Old 19th February 2020, 01:02 PM   #19
freebee is offline freebee  Netherlands
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Your solder joints look fine to me apart from a few blobs, and some look a bit greyish (this could be a cold solder joint). I would use a solder pump to remove the solder and resolver it with fresh solder (perhaps even using a bit of flux depending on the type of solder).
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Old 19th February 2020, 01:05 PM   #20
freebee is offline freebee  Netherlands
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I normally clean my solder work with a bit of alcohol an a toothbrush to make sure there's not a bit of solder stuck somewhere where it shouldn't be.
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