Videopac+ G7400 PSU

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qq1975b
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Joined: Mon Sep 18, 2017 10:16 pm

Re: Videopac+ G7400 PSU

Post by qq1975b » Tue Jan 05, 2021 5:47 pm

I focused only on the PSU that works Ok. I have replaced all the caps and now I get 5.16V and 10.86V when loaded. So I think it is OK now because they are in the admisible values you told me. I have also replaced all the caps on the motherboard, replaced the power switch and installed a switch to turn on and off the Plus graphics. It works fine. Thank you for your help because I didn’t know which voltage values were OK to don’t burn anything.

I do not know what happened to the other PSU. I won’t use it because I don’t know how to fix it. So I won’t be able to use one of the Videopac. :(

Thank you!

Maximilian
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Re: Videopac+ G7400 PSU

Post by Maximilian » Tue Jan 05, 2021 10:04 pm

Last ditch attempt: :)

1. Put one small 12V fan on the 12V line (Black to GND an Red to 12V)
2. Put a couple of bigger 5V and/or 12V fans on 5V (Black to GND an Red to 5V)
3. You should get pretty much around the voltages of the first measurement and all fans should be turning,
if not check that the capacitors are the correct way around, If any were turned backwards just through those away and get new ones.
4. If you sill do not have pretty much the same values of the first measurement, stop and ask a specialst.

If that works you can then:
1. Turn back the pot to its original settings, the 5V should go up from 4,97V to 5V
2. Check the voltage of the 12V line.

If the 12V line is still more than 13V do the following:
1. Disconnect the mains and then the fans.
2. Get the value's from the resistors R158 and R220 from the manual and check them, if not correct within 5-10%,
desolder one side and check the value's of the resistors again, resolder if done.
(If you cannot get the value's of those resistors from the manual please make a closeup picture of those two resistors so we can have a look.)
3. Replace the faulty resistor if any, make sure to use the same wattage resistor.
(the size of the resistor normally is an indication of the wattage, when in dobt use a bigger wattage resistor)
4. If you replaced one or more of the resistors please test again with the fan setup.

If that doesn't work please stop and ask a specialst.

qq1975b
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Joined: Mon Sep 18, 2017 10:16 pm

Re: Videopac+ G7400 PSU

Post by qq1975b » Sat Jan 09, 2021 5:04 pm

OK, I will replace all caps again. No one is fit in reverse. And check all you told me.

I’ll be back 8-)

Maximilian
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Re: Videopac+ G7400 PSU

Post by Maximilian » Sat Jan 09, 2021 6:04 pm

if they all were soldered the correct way the first time, you don't need to replace them.

qq1975b
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Re: Videopac+ G7400 PSU

Post by qq1975b » Wed Jan 13, 2021 7:38 am

The caps are all correctly placed. I have checked the two resistors and are OK too but the 5V fans don’t move and the 12V one runs too fast.
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Re: Videopac+ G7400 PSU

Post by exxos » Wed Jan 13, 2021 10:52 am

Check the output diodes ?
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qq1975b
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Re: Videopac+ G7400 PSU

Post by qq1975b » Wed Jan 13, 2021 5:41 pm

I have checked them and they seem wrong. Others on the pcb are OK.

qq1975b
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Re: Videopac+ G7400 PSU

Post by qq1975b » Thu Jan 14, 2021 6:43 pm

The D189 was totally broken from below. I have replaced it and now the PSU works fine: 5.15V and 11.22V

Thank you all for your help!

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Re: Videopac+ G7400 PSU

Post by exxos » Thu Jan 14, 2021 6:48 pm

:bravo: :girldance: :girldance: :cheer: :cheer:
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Maximilian
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Re: Videopac+ G7400 PSU

Post by Maximilian » Thu Jan 14, 2021 7:00 pm

Well done!!

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