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Old 1st Feb 2023, 1:38 pm   #1
condense
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Default Nordmende Othello E302 - sound only one side

Hello
I thought I had done a reasonable restoration on this having replaced the electrolytic and most of the usual suspect caps. I am still fairly new to this being only on my 6th set so please bear with me.

It worked fine for a month and now has developed an issue where sound is only coming through one side (RHS) of the stereo speakers. There is a slight hum although clearly no signal. When I gently tapped the relevant ECC83 i can hear a crackle so I think it is that no audio signal is getting through
I thought it might be the caps on the PCB which I hadn't replaced (the ones generally to the left of the blue stars on the pic). I replaced all those above 15nF which was a right fiddle but my problem is unchanged.

I even swapped the EL84s which again hasn't made a difference. I've also tried swapping the ECC83s around and that doesn't help either.
Coincidentally the EM84 now looks overloaded when I have a station tuned as well. The balance control seems to work in that it quietens the one side. I swapped the connections of C201 and C202 and that just made the balance work the other way around but still no LHS speaker sound.

I think I may be looking in the wrong place so would welcome any advice.
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Last edited by condense; 1st Feb 2023 at 1:57 pm. Reason: Additional info
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Old 1st Feb 2023, 1:42 pm   #2
Edward Huggins
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Default Re: Nordmende Othello E302 - sound only one side

Changing all those caps may not have been such a good idea. For starters, have you checked the LHS speaker voice coil for continuity?
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Old 1st Feb 2023, 2:05 pm   #3
Station X
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Default Re: Nordmende Othello E302 - sound only one side

Most easily done by swapping over the speakers.
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Old 1st Feb 2023, 4:56 pm   #4
condense
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Default Re: Nordmende Othello E302 - sound only one side

Thank you
The speaker set up is fairly complicated but I am getting 3Ohm on both main speakers and 4ohm on the tweeters. Any ideas what I should try next ?
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Old 1st Feb 2023, 5:18 pm   #5
Edward Huggins
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Default Re: Nordmende Othello E302 - sound only one side

If you are getting 3 ohms on the main speakers that would be correct.
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Old 4th Feb 2023, 7:59 pm   #6
Silicon
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Default Re: Nordmende Othello E302 - sound only one side

There seems to be a switching arrangement for the signal sources.

I would look there first.

Can you introduce a signal to both channels of the audio amplifier via the DIN sockets?
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Old 4th Feb 2023, 9:27 pm   #7
condense
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Default Re: Nordmende Othello E302 - sound only one side

Thank you
I suspect you are right
It seems to be in a very complicated looking volume and balance control pot. I connected the speakers the other way around and the speaker is fine. There are lots of speaker connection and they all seem to work except one - the one which goes from the speaker (I7 or I6)
Iíve tested all resistors and caps back from there to pin 8 on the ECC83s
Iíve still got some more to check but am thinking I will need to get that pot out and take it apart - it has about 15 connections so I am avoiding it until I have run out of ideas
Any other suggestions very gratefully received

It does the same when I use the din socket as well
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Old 7th Feb 2023, 8:54 pm   #8
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Default Re: Nordmende Othello E302 - sound only one side

If it was my Nordmende: Before touching these complicated pots I would start touching pin 2 of each ECC83 with a metal screw driver. This would induce a hum to the grid of the pre-amp stage. Can you hear a somehow humming noise from the speaker? Yes: ECC83 and final amp are good. No: Further research required. Touch pin 7 of each ECC, touch pin 2 of the each EL. Measure the voltages of all cathodes and anodes of the amp as denoted in the circuit diagram.

Sometimes some checking of voltages can save a lot of solder.

Regards, Joe
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Old 8th Feb 2023, 4:12 pm   #9
condense
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Smile Re: Nordmende Othello E302 - sound only one side

Thank you
That is very sound advice.
I have been testing out different parts by switching across between the 2 channels (lucky itís a stereo set!)
I narrowed it down to the ECC83 section and then discovered the earth lead to one was loose. Canít believe it as I was sure I checked that!
Rewired it and the set is back up and running

Interesting that this must have been what caused the issue all along and it must have spontaneously broken off. It was a stiff and brittle wire and looked like it was in place.

Thank you to everyone for your help - it got me there in the end !
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Old 8th Feb 2023, 5:48 pm   #10
Mr 1936
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Default Re: Nordmende Othello E302 - sound only one side

Hi condense

Glad you are "firing on two cylinders" now !

For the future, you might find it useful to get yourself an audio signal generator for signal injection and fault tracing. A simple naked PCB type running from a 9 volt battery is available on the usual online site for only about a tenner.

Another thing I use all the time is a "headband magnifier", which gives you typically x3 magnification with stereoscopic vision. Great for spotting tiny defects, cracks in PCB tracks etc.

I tend to be a bit selective when it comes to replacing components, normally routinely do any paper type grid couplers and AGC couplers plus any resistors that are more than 20% out. Anything else is presumed innocent unless measurement proves otherwise. If it's for someone else I might play safe and replace more extensively but it depends on the vintage of the set and where it has been stored.
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