Nordmende Othello E302 - sound only one side - UK Vintage Radio Repair and Restoration Discussion Forum

condense · 1st Feb 2023, 2:38 pm

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.

Edward Huggins · 1st Feb 2023, 2:42 pm

Changing all those caps may not have been such a good idea. For starters, have you checked the LHS speaker voice coil for continuity?

Station X · 1st Feb 2023, 3:05 pm

Most easily done by swapping over the speakers.

condense · 1st Feb 2023, 5:56 pm

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 ?

Edward Huggins · 1st Feb 2023, 6:18 pm

If you are getting 3 ohms on the main speakers that would be correct.

Silicon · 4th Feb 2023, 8:59 pm

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?

condense · 4th Feb 2023, 10:27 pm

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)
I’ve tested all resistors and caps back from there to pin 8 on the ECC83s
I’ve 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

Joe_Lorenz · 7th Feb 2023, 9:54 pm

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

condense · 8th Feb 2023, 5:12 pm

Thank you
That is very sound advice.
I have been testing out different parts by switching across between the 2 channels (lucky it’s a stereo set!)
I narrowed it down to the ECC83 section and then discovered the earth lead to one was loose. Can’t 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 !

Mr 1936 · 8th Feb 2023, 6:48 pm

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.

1st Feb 2023, 2:38 pm	#1
condense Tetrode Join Date: Jun 2012 Location: Cardiff, Wales, UK. Posts: 79	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. Attached Thumbnails Last edited by condense; 1st Feb 2023 at 2:57 pm. Reason: Additional info

1st Feb 2023, 2:42 pm	#2
Edward Huggins Dekatron Join Date: Sep 2015 Location: Southwold, Suffolk, UK. Posts: 8,328	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? __________________ Edward.

1st Feb 2023, 3:05 pm	#3
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,288	Re: Nordmende Othello E302 - sound only one side Most easily done by swapping over the speakers. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

1st Feb 2023, 5:56 pm	#4
condense Tetrode Join Date: Jun 2012 Location: Cardiff, Wales, UK. Posts: 79	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 ?

1st Feb 2023, 6:18 pm	#5
Edward Huggins Dekatron Join Date: Sep 2015 Location: Southwold, Suffolk, UK. Posts: 8,328	Re: Nordmende Othello E302 - sound only one side If you are getting 3 ohms on the main speakers that would be correct. __________________ Edward.

4th Feb 2023, 8:59 pm	#6
Silicon Nonode Join Date: Jun 2007 Location: Coulsdon, London, UK. Posts: 2,163	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?

4th Feb 2023, 10:27 pm	#7
condense Tetrode Join Date: Jun 2012 Location: Cardiff, Wales, UK. Posts: 79	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) I’ve tested all resistors and caps back from there to pin 8 on the ECC83s I’ve 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

7th Feb 2023, 9:54 pm	#8
Joe_Lorenz Hexode Join Date: Dec 2019 Location: Hohenroda, Eastern Hesse, Germany Posts: 461	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

8th Feb 2023, 5:12 pm	#9
condense Tetrode Join Date: Jun 2012 Location: Cardiff, Wales, UK. Posts: 79	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 it’s a stereo set!) I narrowed it down to the ECC83 section and then discovered the earth lead to one was loose. Can’t 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 !

8th Feb 2023, 6:48 pm	#10
Mr 1936 Heptode Join Date: Mar 2017 Location: Romsey, Hampshire, UK. Posts: 521	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.