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Author Topic: ps-35g pyramid power supply  (Read 1577 times)
KC8MUE
Member

Posts: 4




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« on: November 01, 2003, 09:07:12 PM »

Hello to all, i need help fixing this power supply ,I hooked it up and it powered up with low voltage around 10 volts hooked a radio to it and the voltage dropped right out took the top off and tested for voltage at the transformer and got voltage so i turned the radio back on and the voltage dropped again on the front panel but not at the transformer voltage stayed the same also tried the variable knob on the front and it doesn't do anything , i'm thinking it is the 4 transistors on the back of the supply ,,, any help please
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VE2TUB
Member

Posts: 32




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« Reply #1 on: November 02, 2003, 12:02:03 AM »

It is much cheaper to start by replacing
the 723 regulator IC, as it is the #1
source of voltage problems in PS-35G.
Instal a 14 pin dip socket instead of directly
soldering the new 723, this will make
the next replacement much more easyer!

If a new 723 was of no help, next is the
driver (TIP3055). Check or replace the TIP3055.
Anyway, that part is cheap too, so you can
replace both the 723 and the driver in a one-shot.

If a new driver was of no help, now it's time
to think about replacing the four expensive 2N3772.

Also, check filter caps (6800uF 25V X5).
25V is a bit too low, and many of the units I
fixed had "pressurized" filter caps with rounded tops.
If it's your case, replace all the 5 caps with
35V ones.

73 de VE2TUB
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KC8MUE
Member

Posts: 4




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« Reply #2 on: November 02, 2003, 08:41:07 AM »

that is what i will do thank you for your help,,, i just bought the supply at zealand hamfest for $20 so hopefully i can get it running for pretty cheap thank you again

73 to you and god bless
   kc8mue
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W9GB
Member

Posts: 2623




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« Reply #3 on: November 02, 2003, 10:00:10 PM »

Here is a very useful web site (tutorial and diagrams):
http://www.kbt-dc-supplies.com/index.php

Known problem with this supply is the under rated (voltage) filter capacitors.

w9gb
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KE4MOB
Member

Posts: 721


WWW

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« Reply #4 on: November 04, 2003, 12:12:30 AM »

Just an FYI...if you spent $20 on it, and if EVERYTHING (LM723, TIP 3055, 2N3772s and SCR) is blown, expect to put down about another $20 in parts.

Remarkably, most everything is available at Radio Shack!!

In other words, you got a nice find that without too much trouble will be worth more than what you got in it...
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KC8MUE
Member

Posts: 4




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« Reply #5 on: November 17, 2003, 11:31:53 PM »

thank you guys for the help the supply is up and running with only $12 spent on parts and an extra thanks to ken k8yyc for help 73 good luck all
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