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:
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:
U732 (7812,+12V regulator Ic) 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.