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MTX JH1200 repair
MTX JH1200 repair
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Old 23rd November 2020, 09:47 AM   #21
Perry Babin is offline Perry Babin  United States
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There could be multiple thermistors.

Are the regulators fed off of the emitters of the two transistors near the diodes you replaced?
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Old 23rd November 2020, 10:03 AM   #22
tobyret2 is offline tobyret2
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no. they are powered from the transistor emitters on the driver board. I think all the problems are in the power supply + -15v. On tip29 bases tip30 comes 70v, so it should be?
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Old 23rd November 2020, 10:05 AM   #23
tobyret2 is offline tobyret2
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Quote:
Originally Posted by Perry Babin View Post
There could be multiple thermistors.

Are the regulators fed off of the emitters of the two transistors near the diodes you replaced?
next to the diodes in the photo tip29c tip30c from the emitters of which there is a voltage on the lm317 lm337
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Old 23rd November 2020, 10:18 AM   #24
Perry Babin is offline Perry Babin  United States
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Install a 25v Zener in place of the diodes you replaced. That will make the TIP transistors run hotter and will make the regulators run cooler. It will also help with their reliability since they're only rated for 40v.
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Old 23rd November 2020, 10:32 AM   #25
tobyret2 is offline tobyret2
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15v zener diode will not be enough? Should there be an NPN or PNP transistor in the lm317 power circuit?
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Old 23rd November 2020, 10:43 AM   #26
Perry Babin is offline Perry Babin  United States
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The two preregulators are NPN and PNP.

You could install two Zeners in series if you don't have anything near 25v. The regulators need a bit of headroom over the regulated voltage to work properly.
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Old 23rd November 2020, 12:34 PM   #27
tobyret2 is offline tobyret2
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Nothing works. The transistor heats up strongly if the load is lm ***. Am I doing the right thing, before the lm337 is a PnP transistor? to its base a zener diode 22v which makes -22v. Total obtained on the basis of PnP transistor -22v collector -80v emitter -22v
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Old 23rd November 2020, 05:24 PM   #28
Perry Babin is offline Perry Babin  United States
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What is the DC voltage on all 3 terminals of each regulator?
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Old 24th November 2020, 09:43 AM   #29
tobyret2 is offline tobyret2
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lm337 1- -13.5 2- -22 3- -15
lm317 1 13.5 2- 15 3- 22
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Old 24th November 2020, 10:27 AM   #30
Perry Babin is offline Perry Babin  United States
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That establishes the fact that the transistors are pre-regulators. I don't know if they are the voltage source for any other components.

If not, use a zener value that causes the heat to be distributed evenly between the regulators and the pre-regulator transistors. The voltage between the input and output of the individual regulators can't be more than 40v. Anything below that is safe.
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