| Polarity Switch for K-250 [message #24836] |
Wed, 30 March 2016 15:43  |
slk854
Messages: 192
Registered: January 2015
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Senior Member |
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I know this has been addressed here before, but need to confirm a few things. I just picked up another K-250-4 and a new power cord was installed, but the guy who did it un-soldered all of the connections to the switch, so it does not light up at all. So I am assuming if I get all of the wires back in place like they were I will be OK??????I will snap a shot of what he did and post if that makes it easier to tell me.
Steve
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| Re: Polarity Switch for K-250 [message #24837 is a reply to message #24836] |
Wed, 30 March 2016 16:03  |
chicagobill
Messages: 2006
Registered: April 2003
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Senior Member |
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Are you trying to make the polarity switch work again or just light up?
Normally there are 4 wires that go to the switch:
1-AC Hot
2-AC Neutral
3-Pilot lamp hot
4-Pilot lamp ground
The ground cap also connects to the switch and connects to the chassis at the front panel.
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| Re: Polarity Switch for K-250 [message #24839 is a reply to message #24836] |
Wed, 30 March 2016 17:20 |
chicagobill
Messages: 2006
Registered: April 2003
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Senior Member |
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I see that the polarity switch is broken like they typically are. You might want to add a couple of cable ties to hold the switch to the mounting bracket, to keep it from being damaged any further.
The bulb connects to the two terminals on the back of the switch. The black ground wire is still there and the other terminal should connect with a green wire to the 400 ohm power resistor that is screwed to the chassis that connects to the negative power supply line.
If you look at the power switch, it has a red wire that goes to the 400 ohm resistor that is connected to the positive power supply line. Follow it back and hopefully you will find that the resistor is still there and you will just need to run a new green wire to the back of the polarity switch.
And no, with a grounded cord there should be no need to have a working polarity switch.
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| Re: Polarity Switch for K-250 [message #24841 is a reply to message #24836] |
Wed, 30 March 2016 20:54 |
chicagobill
Messages: 2006
Registered: April 2003
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Senior Member |
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The round black thing with the two terminals is the thermal cut off switch. It is there to shut down the amp if it overheats. I don't know why it was disconnected, maybe it's bad.
The death cap is the blue cap that is connected to the polarity switch and connects to the front panel.
The wiring was changed when the heat sensor was disconnected. The cord that was installed is color coded for Europe, not the US. It may have been a computer IEC cord that has the IEC end cut off.
The photo that shows the red and green wires looks like the green wire was just disconnected from the back of the polarity switch. If you follow it back it should connect to the 400 ohm resistor. If it still does, then just reconnect it to the polarity switch.
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| Re: Polarity Switch for K-250 [message #24843 is a reply to message #24836] |
Thu, 31 March 2016 02:27 |
chicagobill
Messages: 2006
Registered: April 2003
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Senior Member |
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If it is working correctly, I would rewire the thermal cutoff back in. I don't have any good reason for not having it in circuit.
To test the cutoff, see if it has continuity across the two terminals. If it does have continuity then, remove it from the heatsink and test to see if it opens when it is heated up. I think that the temp rating is something like 180 degrees, so you will need a heat gun or hair dryer.
Or if it does have continuity across the terminals, you could just assume that it is working and wire it back in without heat testing.
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| Re: Polarity Switch for K-250 [message #24851 is a reply to message #24836] |
Fri, 01 April 2016 17:39 |
chicagobill
Messages: 2006
Registered: April 2003
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Senior Member |
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Did you reconnect the ac line (hot and neutral) to the polarity switch? If you did, then remove the death cap. If there is no ac running to the polarity switch, then it doesn't matter if the switch stays or goes.
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