On 07/03/2018 03:35 PM, Ian Finder via cctalk wrote:
On Tue, Jul 3, 2018 at 1:21 PM, Monty McGraw via cctalk <
cctalk@classiccmp.org> wrote:
I've been repairing my Tektronix 4052.
I've got the digital logic working - but the text and graphics are messed
up.
I posted photos of the screens in my Tektronix 4052 troubleshooting thread
on vcfed.
With a scope on the final X amplifier stage - it is oscillating - so I see
weird horizontal strokes instead of dots for text. I know from the service
manual that this circuit includes a feedback loop, and with the scope I see
oscillation all around the loop - so I haven't found the source.
If it is basically working, but just has oscillation, then
it is almost certainly a capacitor issue.
There are likely capacitors in the feedback loop to reduce
bandwidth, and decoupling capacitors
on the power rails. It would be fairly easy to track down
the specific capacitors from the manual and check them.
Jon
