Author Topic: Trouble shooting an original Model T  (Read 920 times)

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Offline brennansrevenge

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Trouble shooting an original Model T
« on: July 26, 2005, 04:52:45 pm »
i've got the wiring diagram, and replaced the transformer and 90% of the circuits, but can't stablize my power transformer.

i'm burning up the R43 330 ohm resister.  any thoughts?

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Offline Isaac

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Trouble shooting an original Model T
« Reply #1 on: July 27, 2005, 08:29:11 am »
My first thought is that C15 is leaky, drawing a high current through R43 and CR1. Have you replaced that? Is there any sign of abnormal operation, like swelling or heat?
Isaac

Offline brennansrevenge

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Trouble shooting an original Model T
« Reply #2 on: July 27, 2005, 09:44:33 am »
abnormal operation?? sorry i just laughed because it hasn't operated since 1994.  thank you for the response, i do appreciate the help!

i did replace all of those components in their proper arrangement.  

do you think that a shorted tube or cap can cause a large voltage to ground?

Offline Isaac

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Trouble shooting an original Model T
« Reply #3 on: July 27, 2005, 08:28:08 pm »
Of course. If the cap is shorted, or has a low DC resistance due to age or poor dielectric, then R43 will have to drop all of the voltage from the transformer. In this case, that's 55 volts.Since P=E^2/R, R43 has to dissipate at least 9 watts. What is it rated at?
Isaac

Offline brennansrevenge

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Trouble shooting an original Model T
« Reply #4 on: July 29, 2005, 07:17:08 pm »
all resisters are rated for 1/2w, except for the pots, and some other specific resisters.

i've been talking with Joe Arthur on the Q&A side and took some measurements:

i did measure the diode and it's good.  the caps are going the correct direction, and finally readings: R44= 6.5K (10K) and R45=14K(18K)

by the way when i am blowing R43, the standby is off, so only the heaters are going.

I checked caps 15,16,19, & 20 and they read over 15K of resistance, they build resistance to about 150K.