Looking for Tektronix 4051 or 4052 Display Board

[Brent Hilpert]

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:
>> 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.


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.