A fine job of isolating the main problem and improving things to prevent a recall incident. And it never hurts to have a happy customer because they do not need to return it with the same problem!
Mend it Mark, XrayTonyB Mr. Carlson`s is good too. But anyone who keeps alive the vintage gear great. The new stuff is not always better. But yeah all these old guys need a complete clean, noisy transistors replaced, and out of tolerance parts replaced. Rebias, and make sure DC offset is not a concern. I hate dirty flakey switches. So again clean, and service. Capacitors check for ESR, and again out tolerance issues. All kinds of cool gear is out there for test. I like the idea using both sets of contacts and the snubber Capacitor. Should have been that way from the factory, instead of dumping all that current on that power switch. Good work there. Keeping vintage sounding good, and alive is why I am alive.
I suspected the amp came with a snubber capacitor from the factory. I checked the service manual and yes there should be A 10nF capacitor across the switch. The previous tech that rewired the switch cut out the capacitor and threw it away? They got it working again but the missing cap accelerated the switch wear
The reason for the double pole switches is that in some regions (country's), it's mandatory to switch both Live and Neutral. If you check the schematics you will see that the 220Volts and the 240Volts versions of the amp uses both poles of the switch. It's only in the US and multi-voltage version that only uses that one pole. On the 110 - 120Volts version they should have used both poles in parallel as you did since those will draw twice as much current as the 200+ voltages versions will.
Good save. Mark over on the "Mend it Mark" channel can rebuild the contacts using a process involving a few different chemicals to lay down silver plate on the contact surface if the contacts are totally shot. I found his channel during your hiatus while you were off playing the hairy banjo.🪕
AgSnO2 alloy is used on modern relay contacts, where high in-rush currents are involved, silver and gold work best with low power and signal application, but the former tarnishes over time. Still, way, way better than nothing where obsolete swotches are involved.
I remember watching that video and asking myself WHY??? Any plating will be removed by the arc within the first few cycles. Power switches need to have a silver or silver alloy button otherwise the contact area will get destroyed by the arc. Silver is used because it's the best conductor of heat (and electricity) The arc generates intense heat and plasma for a split second. The silver button keeps cool enough that the metal doesn't get vaporized as much as other metals, like copper would. Notice how the levers do not have buttons welded on and are just a stamped piece of copper with a plating. The levers are ate away from the arc and the buttons (on the stationary side) are mostly intact. The black stuff I cleaned out isn't carbon but rather vaporized metals of silver and copper oxides. A good quality switch for power use will have silver buttons on both contacts, not just one side. Relays are a good example of this. They have two buttons at the contact
Good to see ya back Trevor and yes remember this JVC. My Cat the same thing, my electronics is a Cat heater. Always enjoy a switch tear down, and a film cap for a soft start would have prevented this issue. Charcoal charcoal charcoal. I think that little stray wire was grounding it out.
When you have a switch in a circuit that powers a large inductor (the transformer acts like a inductor), almost everytime you open the switch you will have a high voltage pulse generated by the collapsing magnetic fields of that inductor. The pulse can be several kV and microseconds in duration and can have a high energy. That energy released at the contacts can arc and vaporize the switch contacts. A capacitor across the switch contacts will act to shunt this pulse and allow somewhere for that energy to go thus reducing the arc and increasing the life of the contacts.
Great work, i would like to see someone work on a MAC 1900 receiver my left channel went up in a little puff of smoke. It had been running a little hot prior. 😢
A nice robust solution for a burnt out switch that will prevent it happening again ! Like you say, it's silly using a dual pole switch and not using both sets of contacts. I suspect they intended to use both sides when they chose the switch but then someone in the manufacturing department thought they didn't need to so they omitted the jumpers, it may even have been a time or cost saving thing !
What I would do is get a relay rated for 120 volts ac on the coil use the switch to control the relay and have the relay take the load of the amplifier
Nice one. The JVCs from that era are not as popular as the big names. Do you have any opinion as to how this JVC line-up compares to the more common brands from that era in regards to sound and build quality? I was occasionally looking for one of this line-up simply for the front inputs, but they seem to be pretty rare in Europe.
A fine job of isolating the main problem and improving things to prevent a recall incident. And it never hurts to have a happy customer because they do not need to return it with the same problem!
Great work diagnosing the fault down to the switch. I like the way you narrowed it down to the switch using continuity test. Excellent work!
Great job, this is exactly what i would have done to the power switch : contacts in parallel and a snubber capacitor !
Nice to see that amp back on the table again! I have the same model myself, and it's definitely in need of some care as well.
Great stuff. Well diagnosed and work around.
Mend it Mark, XrayTonyB Mr. Carlson`s is good too. But anyone who keeps alive the vintage gear great. The new stuff is not always better. But yeah all these old guys need a complete clean, noisy transistors replaced, and out of tolerance parts replaced. Rebias, and make sure DC offset is not a concern. I hate dirty flakey switches. So again clean, and service. Capacitors check for ESR, and again out tolerance issues. All kinds of cool gear is out there for test. I like the idea using both sets of contacts and the snubber Capacitor. Should have been that way from the factory, instead of dumping all that current on that power switch. Good work there. Keeping vintage sounding good, and alive is why I am alive.
I suspected the amp came with a snubber capacitor from the factory. I checked the service manual and yes there should be A 10nF capacitor across the switch.
The previous tech that rewired the switch cut out the capacitor and threw it away? They got it working again but the missing cap accelerated the switch wear
The reason for the double pole switches is that in some regions (country's), it's mandatory to switch both Live and Neutral.
If you check the schematics you will see that the 220Volts and the 240Volts versions of the amp uses both poles of the switch.
It's only in the US and multi-voltage version that only uses that one pole.
On the 110 - 120Volts version they should have used both poles in parallel as you did
since those will draw twice as much current as the 200+ voltages versions will.
Good save. Mark over on the "Mend it Mark" channel can rebuild the contacts using a process involving a few different chemicals to lay down silver plate on the contact surface if the contacts are totally shot. I found his channel during your hiatus while you were off playing the hairy banjo.🪕
Mark is the most amazing tech I've ever watched. Creates his own PC boards from scratch, winds his own motors, crazy British sense of humour.
AgSnO2 alloy is used on modern relay contacts, where high in-rush currents are involved, silver and gold work best with low power and signal application, but the former tarnishes over time. Still, way, way better than nothing where obsolete swotches are involved.
I remember watching that video and asking myself WHY??? Any plating will be removed by the arc within the first few cycles.
Power switches need to have a silver or silver alloy button otherwise the contact area will get destroyed by the arc.
Silver is used because it's the best conductor of heat (and electricity) The arc generates intense heat and plasma for a split second. The silver button keeps cool enough that the metal doesn't get vaporized as much as other metals, like copper would.
Notice how the levers do not have buttons welded on and are just a stamped piece of copper with a plating. The levers are ate away from the arc and the buttons (on the stationary side) are mostly intact. The black stuff I cleaned out isn't carbon but rather vaporized metals of silver and copper oxides.
A good quality switch for power use will have silver buttons on both contacts, not just one side. Relays are a good example of this. They have two buttons at the contact
Good to see ya back Trevor and yes remember this JVC. My Cat the same thing, my electronics is a Cat heater. Always enjoy a switch tear down, and a film cap for a soft start would have prevented this issue. Charcoal charcoal charcoal. I think that little stray wire was grounding it out.
Good to see you back Trev!
Thanks
Très bel appareil, du vrai haut de gamme d'époque, bravo ! 😉
Nice looking amp.
Keep the amp clean! People often neglect that part.
Nice repair Trevor :-D
I always took the switches/pots apart, rather than buy new.
If it can be serviced, it saved them money.
Nice Jvc amp 👍
Welcome back. We mised you!
Merci, very interresting. I didn't understand the point of the capacitor on the switch please?
When you have a switch in a circuit that powers a large inductor (the transformer acts like a inductor), almost everytime you open the switch you will have a high voltage pulse generated by the collapsing magnetic fields of that inductor. The pulse can be several kV and microseconds in duration and can have a high energy. That energy released at the contacts can arc and vaporize the switch contacts. A capacitor across the switch contacts will act to shunt this pulse and allow somewhere for that energy to go thus reducing the arc and increasing the life of the contacts.
Great work, i would like to see someone work on a MAC 1900 receiver my left channel went up in a little puff of smoke. It had been running a little hot prior. 😢
A nice robust solution for a burnt out switch that will prevent it happening again !
Like you say, it's silly using a dual pole switch and not using both sets of contacts. I suspect they intended to use both sides when they chose the switch but then someone in the manufacturing department thought they didn't need to so they omitted the jumpers, it may even have been a time or cost saving thing !
What I would do is get a relay rated for 120 volts ac on the coil use the switch to control the relay and have the relay take the load of the amplifier
whoever designs these huge capacitor monsters without a softstarter mechanism .....
nice work though. 👌
Nice save. Perhaps there were fuses blown because of constant inrush current pulses caused by the poor connection in the power switch.
Nice one. The JVCs from that era are not as popular as the big names. Do you have any opinion as to how this JVC line-up compares to the more common brands from that era in regards to sound and build quality?
I was occasionally looking for one of this line-up simply for the front inputs, but they seem to be pretty rare in Europe.
Al I know is the owners are very happy with the sound quality. I was pleased too for the short time I used it. Solid build quality and great performer
Where have you been?, I thought you might be frazen likk Jack Torrace up there in Canada EH!
Busy playing my hairy banjo apparently, lol
welcome back, did you do the citation tuner?
Thanks, not yet
What capacity, brand and type of snubber cap did you use?
I used a 10nF ceramic disc rated X1 class
@@TrevorsBench Thanks
Вот это вещь🔥
Bom dia daqui de portugal
L would stap both side's together after your repair & fit snubber cap
But if you wear out both ends of the switch you will have a problem next time. Maybe would be better to not use the last contact.
At that point the amp should be close to 100 years old
I hate those darn boomerangs!!!
Install a triac and the switch will work forever!