Tek 577 D1 Repair (B07xxxx)


1. 2020-Oct-24 :replaced a leaking electrolytic capacitor C124 on the A2 collector supply circuit board.

2. Oct-26 :The Collector supply disabled light turned on right at power on.
only one small spot could be seen on the screen.

Power consumption dropped from normal ~60W down to 51~52W.
Checked A3 power supply board:
+5V +5.12V
+12V +12.12V
-12V +0.72V<------NG!
+30V +29.83V
-30V -29.85V
+200V +191Vdc
+40V +40.07V
-40V -40.02V

U732 IC(7812,the -12V regulatpr IC on A3 board):
Input pin:+21.18Vdc ok! (should be +9.5V under normal conditions)
Common pin:+0.72 NG! (-12V)
Output pin:GND(0v) ok!

Replaced the U732(uA7812,1.5A) with a ST L7812CV(1.5A) on Oct-27 and fixed the issue.
I also replaced the U722 IC (+12V regulator IC,7812) and adjusted +30v/-30V to within +-0.2%(specs:+-0.5%).

3. Oct-29: A1 main board shorted

The traces disappeard suddenly after power on for about 30min,only an fine slant line about 2mm long could be seen.(it's a good news,much better than nothing on screen)
After inspections I found:
Power consumption jumped to ~90W(normal:~60W)
A3 power supply board:
+12V +0.6V<-------NG!
-12V -12.09V
+200V +191Vdc
-30V -29.98V
+30V +29.95V

U732 (7812,+12V regulator Ic) ok!
CR722 ok!
The resistance between +12v and GND: 0.5 ohm!
Some shorted part brought the +12V down to +0.6V and consumed about 30W!(it's about 2.5A if all come out of +12V rail)

After disconnecting P722 from A3 board the resistance between +12V and GND became about 2.3K ohm.this led me to A1 main board.
today I found the shorted part,it's C297 (15uf/20v,20% electrolytic capacitor).

I replaced the C297 with a panasonic 22uf 35V capacitor.

The Tek 577 D1 is in good working condition now except some noises(high frequency ripple) on the traces it comes and goes from time to time,
I will deal with it later.

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