3 Jul
2018
3 Jul
'18
6:54 p.m.
On 2018-Jul-03, at 5:59 PM, Jon Elson via cctalk wrote:
On 07/03/2018 03:35 PM, Ian Finder via cctalk wrote:
I had the same initial thought, but Monty's msgs & scope trace show a solid ramp
waveform down around 37Hz, not the higher F ringing or transient sort of sine oscillation
one would expect from failed small-C bypass/suppression/etc. caps. It's more like a
relaxation-oscillator type of activity. He's already replaced a couple of the larger-C
caps in the circuit.
On Tue, Jul 3, 2018 at 1:21 PM, Monty McGraw via
cctalk <
cctalk at 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.