Never soldered from new - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

G4YVM David · 29th Mar 2017, 2:14 pm

Ah!! Many lessons in one post. Many thanks

D

Argus25 · 30th Mar 2017, 12:42 pm

I saw something similar once in an Eddystone 640 communications radio. I performed an alignment on it, the coils are in a die cast enclosure. One coil wasn't responding to adjustment normally. On looking, it was completely missing a short wire link that joined one of its terminals to another nearby wire. On close inspection, it was never soldered from new and the link wire was missing as well. Yet this slipped through the factory inspection and the factory alignment process too. I was so surprised by it, it stuck in my memory.

emeritus · 31st Mar 2017, 5:08 pm

We were plagued for years with a noisy phone line where the fault always cleared when the engineer sent a test tone down the line. An engineer did eventually admit that the application of the test tone could sometimes make a poor connection good, and said that we could probably fix it ourselves by calling our number from another phone, which did actually work for some years. Only after we got broadband was the source of the poor connection eventually traced to a broken wire at the insulation-displacement terminal block in our street pole.

Argus25 · 2nd Apr 2017, 8:33 am

I had heard of that phone line issue before, clearing with the ringing current, very difficult to find.

It is interesting what can happen at the junction between two dissimilar metals that oxidize over time. I once had a TV (80's vintage IC based) with very distorted audio. Looking at the scope the input to the audio amp looked like it had been half wave rectified. It turned out to be an oxidized fitting on a molex plug carrying the low level audio signal, and it was acting as a poor quality diode. However other connections on the connector carrying higher currents were ok.

It was said once that it takes about 20 to 50mA to keep switch contacts clean. If the currents are in the nA range, it doesn't take much oxidation for the switch to apparently fail. In Kettering auto ignition systems with electronic assist on the contact breakers, it is customary to run about 70mA via the contacts.

m0cemdave · 2nd Apr 2017, 9:20 pm

I have encountered that problem a few times with high powered loudspeaker circuits. The effect is to cause distortion due to the rectifying junction and it only happens at low signal levels. It sounds very much like the distinctive noise caused by a rubbing loudspeaker cone.

On one occasion it was an XLR3 output connector on an amplifier (back in the days when that was a standard speaker connector) in which the solder hadn't wetted the termination bucket. Finding this was a great relief to the system owner who thought his four Gauss 18" (that means expensive) speakers were kaputt...

On another, I had a rubbing speaker sound on a system that turned out to be a spade terminal on an amplifier binding post. It wasn't quite tight enough and had a surface oxide layer.

Oldcodger · 2nd Apr 2017, 11:32 pm

Many ,many years ago I was on the maintenance team at a large GPO station, where we could regularly get reports of "poor signals on junction routes" - this mainly turned out to be non soldered joints on the frame- someone had run in the audio jumpers ( wiring) ,but the solder tags remained un soldered. My cure was to trace the signal, with one a lot lower than normal level, as once disturbed, normal signal level "wetted " the joint and "normal service was restored "

emeritus · 2nd Apr 2017, 11:59 pm

An old hand at Plessey told me that, in the days when they used to make TVs, about one in ten wouldn't work when switched on for alignment. The usual cause was oxidised valveholder connections, and they used a rubber mallet to deal with this: a sharp blow would usually bring the set to life.

Nickthedentist · 3rd Apr 2017, 8:14 am

Quote:

Originally Posted by m0cemdave

I have encountered that problem a few times with high powered loudspeaker circuits. The effect is to cause distortion due to the rectifying junction and it only happens at low signal levels. It sounds very much like the distinctive noise caused by a rubbing loudspeaker cone.

The other common cause of this is oxidised contacts on the loudspeaker protection relay. Turning up the volume "cures" it for a while.

N.

29th Mar 2017, 2:14 pm	#21
G4YVM David Heptode Join Date: May 2014 Location: Salisbury, Wiltshire, UK. Posts: 998	Re: Never soldered from new Ah!! Many lessons in one post. Many thanks D

30th Mar 2017, 12:42 pm	#22
Argus25 No Longer a Member Join Date: Oct 2016 Location: Maroochydore, Queensland, Australia. Posts: 2,679	Re: Never soldered from new I saw something similar once in an Eddystone 640 communications radio. I performed an alignment on it, the coils are in a die cast enclosure. One coil wasn't responding to adjustment normally. On looking, it was completely missing a short wire link that joined one of its terminals to another nearby wire. On close inspection, it was never soldered from new and the link wire was missing as well. Yet this slipped through the factory inspection and the factory alignment process too. I was so surprised by it, it stuck in my memory.

31st Mar 2017, 5:08 pm	#23
emeritus Dekatron Join Date: Jan 2012 Location: Brentwood, Essex, UK. Posts: 5,345	Re: Never soldered from new We were plagued for years with a noisy phone line where the fault always cleared when the engineer sent a test tone down the line. An engineer did eventually admit that the application of the test tone could sometimes make a poor connection good, and said that we could probably fix it ourselves by calling our number from another phone, which did actually work for some years. Only after we got broadband was the source of the poor connection eventually traced to a broken wire at the insulation-displacement terminal block in our street pole.

2nd Apr 2017, 8:33 am	#24
Argus25 No Longer a Member Join Date: Oct 2016 Location: Maroochydore, Queensland, Australia. Posts: 2,679	Re: Never soldered from new I had heard of that phone line issue before, clearing with the ringing current, very difficult to find. It is interesting what can happen at the junction between two dissimilar metals that oxidize over time. I once had a TV (80's vintage IC based) with very distorted audio. Looking at the scope the input to the audio amp looked like it had been half wave rectified. It turned out to be an oxidized fitting on a molex plug carrying the low level audio signal, and it was acting as a poor quality diode. However other connections on the connector carrying higher currents were ok. It was said once that it takes about 20 to 50mA to keep switch contacts clean. If the currents are in the nA range, it doesn't take much oxidation for the switch to apparently fail. In Kettering auto ignition systems with electronic assist on the contact breakers, it is customary to run about 70mA via the contacts.

2nd Apr 2017, 9:20 pm	#25
m0cemdave Octode Join Date: Feb 2009 Location: Bletchley, Buckinghamshire, UK. Posts: 1,223	Re: Never soldered from new I have encountered that problem a few times with high powered loudspeaker circuits. The effect is to cause distortion due to the rectifying junction and it only happens at low signal levels. It sounds very much like the distinctive noise caused by a rubbing loudspeaker cone. On one occasion it was an XLR3 output connector on an amplifier (back in the days when that was a standard speaker connector) in which the solder hadn't wetted the termination bucket. Finding this was a great relief to the system owner who thought his four Gauss 18" (that means expensive) speakers were kaputt... On another, I had a rubbing speaker sound on a system that turned out to be a spade terminal on an amplifier binding post. It wasn't quite tight enough and had a surface oxide layer.

2nd Apr 2017, 11:32 pm	#26
Oldcodger Nonode Join Date: Oct 2014 Location: West Midlands, UK. Posts: 2,181	Re: Never soldered from new Many ,many years ago I was on the maintenance team at a large GPO station, where we could regularly get reports of "poor signals on junction routes" - this mainly turned out to be non soldered joints on the frame- someone had run in the audio jumpers ( wiring) ,but the solder tags remained un soldered. My cure was to trace the signal, with one a lot lower than normal level, as once disturbed, normal signal level "wetted " the joint and "normal service was restored "

2nd Apr 2017, 11:59 pm	#27
emeritus Dekatron Join Date: Jan 2012 Location: Brentwood, Essex, UK. Posts: 5,345	Re: Never soldered from new An old hand at Plessey told me that, in the days when they used to make TVs, about one in ten wouldn't work when switched on for alignment. The usual cause was oxidised valveholder connections, and they used a rubber mallet to deal with this: a sharp blow would usually bring the set to life.