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Repairing a 577 that is pretty far gone.


Eric
 

I got most of the repairs complete on a 577 that was pretty trashed I was in to the calibration document to adjusting the vertical amp gain there was very little adjustment. Holding in the beam find button and moving the position know the trace moves up and down but also moves in a J pattern on the crt when moving the vertical position control from clockwise to full counter clockwise. I have tested all 4 transistors and all the resisters in the vertical drive section and they all test with in spec however the amp and drive transistors are VERY poorly matched when it comes to Hfe. Troubleshooting lead me back to U570 which should be a tek 156-0200-00 (AKA MC1456P) what was in the socket was a metal can labeled S 7939 1826 0569. the unit is a very early one display serial number is B010114 the chassis serial is B010124. Power supply checks out OK and is working. Any one know what I can use in replacement of a 156-200?


Dave Casey
 

The 1826-0569 is an HP badged NE5534AT.
The 156-0200 is listed on eBay and also in stock at QService. Why not just
use the correct part?

Dave Casey

On Sun, Oct 11, 2020, 5:35 PM Eric <ericsp@...> wrote:

I got most of the repairs complete on a 577 that was pretty trashed I was
in to the calibration document to adjusting the vertical amp gain there was
very little adjustment. Holding in the beam find button and moving the
position know the trace moves up and down but also moves in a J pattern on
the crt when moving the vertical position control from clockwise to full
counter clockwise. I have tested all 4 transistors and all the resisters in
the vertical drive section and they all test with in spec however the amp
and drive transistors are VERY poorly matched when it comes to Hfe.
Troubleshooting lead me back to U570 which should be a tek 156-0200-00 (AKA
MC1456P) what was in the socket was a metal can labeled S 7939 1826 0569.
the unit is a very early one display serial number is B010114 the chassis
serial is B010124. Power supply checks out OK and is working. Any one know
what I can use in replacement of a 156-200?






Eric
 

I was able to acquire a spare op-amp from a unit that has yet to be repaired but I have some replacements on the way. I am at step 15 of the calibration document. And when I hit the invert switch my spot is off by about .8 divisions. The service manual says I should be off by about 0.1. The + -> AC -> - transition is correct and it is correct inverted but switching between inverted and normal display cause a shift +0.8.


Eric
 

Turns out there was a fault in the 177 that was causing the issue. I will need to look at this 177 very closely. the 577 it seems is ok.

On 10/12/2020 6:38 PM, Eric via groups.io wrote:
I was able to acquire a spare op-amp from a unit that has yet to be repaired but I have some replacements on the way. I am at step 15 of the calibration document. And when I hit the invert switch my spot is off by about .8 divisions. The service manual says I should be off by about 0.1. The + -> AC -> - transition is correct and it is correct inverted but switching between inverted and normal display cause a shift +0.8.