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Tek 577 D1 Repair (B07xxxx)


Jack2015
 

1. 2020-Oct-24 :replaced a leaking electrolytic capacitor C124 on the A2 collector supply circuit board.
https://groups.io/g/TekScopes/photo/255563/6?p=Created,,,100,2,0,0

2. Oct-26 :The Collector supply disabled light turned on right at power on.
only one small spot could be seen on the screen.
https://groups.io/g/TekScopes/photo/255563/3?p=Created,,,100,2,0,0

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

Checked
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).
https://groups.io/g/TekScopes/photo/255563/2?p=Created,,,100,2,0,0

I replaced the C297 with a panasonic 22uf 35V capacitor.
https://groups.io/g/TekScopes/photo/255563/1?p=Created,,,100,2,0,0

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.
https://groups.io/g/TekScopes/photo/255563/0?p=Created,,,100,2,0,0


Jack2015
 

4. (B108xxx,My 2nd 577 D1)
2020-Nov-2~8: Max 8 traces displayed on screen(9 lines included the baseline)

Checked the staircase signal:
Saw only 8 steps, 660mV /per step <-------NG (should be 10 steps,500mV/step)
https://groups.io/g/TekScopes/photo/255563/1?p=Created,,,100,2,0,0

Adjusted the step amplitude VR(A1 Board) and got the staircase of 10 steps (500mV/step).
https://groups.io/g/TekScopes/photo/255563/3?p=Created,,,100,2,0,0
https://groups.io/g/TekScopes/photo/255563/0?p=Created,,,100,2,0,0

5.(B108xxx,My 2nd 577 D1)
2020-Nov-9~15: The Collector supply disabled light turned on right at power on.

Checked Q588(2N2222,50V,0.8A):
Vc=+12V
Vb=+1.3V <-------NG Vbe=+1.3-(-12)=13.3V>>0.7V
Ve=-12V
Vbe open

https://groups.io/g/TekScopes/photo/255563/4?p=Created,,,100,2,0,0

Fixed this issue by replacing the 2N2222 with a 2sc1384(50V,1A).

https://groups.io/g/TekScopes/photo/255563/2?p=Created,,,100,2,0,0