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Old 3rd Mar 2017, 11:31 am   #21
The Philpott
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Default Re: Vintage Radio Solder Joints

I have also noticed in these older 'changed' solder joints that the change of state is slower than normal, it becomes like putty before it melts properly.
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Old 3rd Mar 2017, 11:40 am   #22
Lucien Nunes
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Default Re: Vintage Radio Solder Joints

Quote:
The "S" Correction capacitor or the Line Lin coil would go dry solder.... a neat hole in the pad with the component pin sticking through.
I've also thought about the accelerated failure of joints in line output stages. There are some obvious potential causes of weak / stressed joints from design & manufacture, such as the mass of the LOPT causing the board to flex nearby whenever the set is moved, varnish / encapsulant residue on the leadouts, etc. But after experiencing some striking failures in service, especially one model of SVGA monitor that invariably had O/C connections on the lin coil between 1 & 2 years of daily use from new (sometimes resulting in spectacular board burn-ups) I developed a theory that the joints were being mechanically fatigued by vibration at line frequency. Does anyone have any data to confirm/deny this?
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Old 3rd Mar 2017, 5:59 pm   #23
Silicon
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Default Re: Vintage Radio Solder Joints

When I remove a faulty circuit board I immediately look at the soldered connections of board mounted transformers for that particular type of 'dry joint' which occurs after several years of use.

I am sure that the soldered joints were healthy when they left the factory.

I am inclined to believe it is due to vibration.
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Old 3rd Mar 2017, 6:04 pm   #24
Phil G4SPZ
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Default Re: Vintage Radio Solder Joints

Maybe work-hardening induced by high-frequency mechanical vibration?
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Old 3rd Mar 2017, 10:44 pm   #25
MotorBikeLes
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Default Re: Vintage Radio Solder Joints

I think this type of failure happens with the combination of high frequencies (line frequency sort of high) and high currents. No doubt this can also involve mechanical factors as Lucien suggests.
I used to buy, renovate and sell Grundig CTVs, those with the thyristor line output circuits. I don't think ANY set suffered as many (so called) "drys" as those. I used my Weller gun, getting thro tips and solder at a rapid rate, but after that the sets were reliable, and from my point of view, profitable.
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