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 Post subject: Heathkit IT-28 Cap Checker Resistors Getting Pretty Hot
PostPosted: Mar Mon 12, 2018 7:39 pm 
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Joined: Jan Sun 18, 2015 5:01 am
Posts: 1060
Location: Waxahachie Texas
Guys,
I'm recapping and changing out the resistors in my IT-28. The 4 47K 2W and the 33K 2W resistors are getting quite hot. Like 265 degrees F. Is this normal?


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IT-28 Schematic.pdf [215.35 KiB]
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 Post subject: Re: Heathkit IT-28 Cap Checker Resistors Getting Pretty Hot
PostPosted: Mar Mon 12, 2018 9:01 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 17434
Location: Albuquerque, NM 87123
Seems a little hot to me. Did you replace the two 40uf? I use 47uf at 450 volt. Did you check the wiring and parts against the assembly manual?


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 Post subject: Re: Heathkit IT-28 Cap Checker Resistors Getting Pretty Hot
PostPosted: Mar Mon 12, 2018 9:18 pm 
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Joined: Jan Sun 18, 2015 5:01 am
Posts: 1060
Location: Waxahachie Texas
Johnnysan wrote:
Seems a little hot to me. Did you replace the two 40uf? I use 47uf at 450 volt. Did you check the wiring and parts against the assembly manual?

Yeah, I used some 47uf 450V too. Yeah I checked everything against the manual.

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 Post subject: Re: Heathkit IT-28 Cap Checker Resistors Getting Pretty Hot
PostPosted: Mar Mon 12, 2018 10:54 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 7392
Location: Minneapolis, MN USA
Look at the schematic.

The 33k resistor is a power supply bleeded with 200 volts on it.
That is 1.2 watts of dissipation, which can feel quite hot.

The 47k resistors are part of a series/parallel arranged voltage dropper for the range swith.
Those resistors total 8 watts so major dissipation is expected there.


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