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 Post subject: Grundig Model SO 190 Ua1 Balance control issues
PostPosted: Aug Mon 15, 2022 3:43 pm 
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Joined: May Sun 16, 2021 12:18 pm
Posts: 48
Attachment:
grundig console.jpg
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I recently acquired for free, a Grundig MODEL SO 190 Ua 1 and have begun restoration of this console and may be a little over my head. I have replaced the wax and electrolytic caps and having a few issues with the system. The radio seems to be working well and has a considerably high volume that the phono. I would estimate 20-30% louder on the radio vs phono. There is also no balance control, and the right channel is slightly louder than the left.
I initially thought there was a problem with the balance pot and was dreading having to pull the control to test. The pot is located in a recessed area and difficult to get to.
Attachment:
BAL POT.jpg
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I was able to check the taps by disconnecting the leads at the selector switch and testing the ohm readings. I had readings of 550-.8 and 585-1.3 which would suggest the pot is working correctly.
Attachment:
BALANCE TAPS.jpg
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The schematic for this console is not easy to find but I was able to get a German schematic from Radiomuseum but it has been difficult for me to interpret since I struggle with schematics anyway.
Attachment:
radiomuseum-grundig-so190ua-A.pdf [410.36 KiB]
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Attachment:
radiomuseum-grundig-so190ua-B.pdf [385.33 KiB]
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I’m wondering if anyone can help me track down this balance control issue and where I might start the troubleshooting process. Does anyone know if the volume difference is normal for one of these consoles? I have attached some pics and the schematic.


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 Post subject: Re: Grundig Model SO 190 Ua1 Balance control issues
PostPosted: Aug Mon 15, 2022 4:47 pm 
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Joined: Aug Tue 02, 2022 5:06 pm
Posts: 43
Location: battleford, canada
I'm having trouble following the switch diagram, but I suspect on radio the balance pot is switched out anyway.

Since there is complete separate output stages though, could be any problem in there making one channel weak.


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 Post subject: Re: Grundig Model SO 190 Ua1 Balance control issues
PostPosted: Aug Mon 15, 2022 10:31 pm 
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Joined: Jan Tue 15, 2013 11:04 pm
Posts: 2816
Location: 77001
The volume difference b/t the radio and phono output
is normal.

It is possible the phono cartridge may
have lost some output.

Clean the connectors on the tonearm wiring and the
pins on the cartridge.

If there are RCA phono input jacks, clean them and the RCA
phono cables, or Euro equivalent.

Subbing out a known good cart is an option
to check volume output on Phono.

Do the audio tubes check out good ?

Hotwax


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 Post subject: Re: Grundig Model SO 190 Ua1 Balance control issues
PostPosted: Aug Tue 16, 2022 5:08 pm 
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Joined: May Sun 16, 2021 12:18 pm
Posts: 48
I installed a new cartridge and cleaned all the pins from the phono to the speakers. There is a junction box on both sides of the console that I believe are for secondary speakers. I will be going through these next.
Attachment:
20220816_124742.jpg
20220816_124742.jpg [ 564.58 KiB | Viewed 339 times ]

I have replaced 2 of the EL95 tubes and switched them between different sockets which doesn't seem to affect the variation between the channels. Is there another tube that may have some effect on the channel imbalance?
I am baffled by the balance dial having no effect. Since the pot checks out, where could this issue be?

Thanks


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 Post subject: Re: Grundig Model SO 190 Ua1 Balance control issues
PostPosted: Aug Tue 16, 2022 6:06 pm 
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Joined: Aug Tue 02, 2022 5:06 pm
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Location: battleford, canada
Could be the ECC83s

Looks like you missed a cap in your first picture, is that C62 tied to the switch? (ECC83 'II' cathode bypass, 25uF).

Which piano key is all those marked wires from the pot on?


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 Post subject: Re: Grundig Model SO 190 Ua1 Balance control issues
PostPosted: Aug Tue 16, 2022 8:47 pm 
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Joined: May Sun 16, 2021 12:18 pm
Posts: 48
I'll swap out the ECC83's which appears to be replaceable with a 12AX7 and see if that helps.
I did miss that 25uF cap but tested it and it tests good. I hadn't got around to replacing it, but will get that done as well.
The piano switch with the Bal leads is the "STEREO" switch. I don't have any operating instructions for this unit and wonder if the MONO-PU-STEREO are meant to be pushed simultaneously?
Attachment:
20220816_164124.jpg
20220816_164124.jpg [ 699.04 KiB | Viewed 321 times ]


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 Post subject: Re: Grundig Model SO 190 Ua1 Balance control issues
PostPosted: Aug Tue 16, 2022 9:44 pm 
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Joined: Aug Tue 02, 2022 5:06 pm
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Location: battleford, canada
That makes sense, I think when stereo isn't pressed it bypasses the balance pot and put's the audio from the upper first ECC83 into both chains. In that situation level should be the same unless there is problem with 2nd ecc83 up to the speaker.


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 Post subject: Re: Grundig Model SO 190 Ua1 Balance control issues
PostPosted: Aug Tue 16, 2022 11:26 pm 
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Joined: Jan Thu 01, 1970 12:00 am
Posts: 2813
Location: Carlstadt NJ USA
I believe you push the "Mono PU" button or mono records, and the "Stereo PU" button for stereo records. That's how it worked on the circa 1960 Grundig console I used to have.

If you play your mono records in stereo, only the surface noise will be stereo, which makes the noise more apparent


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