3 Jul
2018
3 Jul
'18
1:21 p.m.
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.
Does anyone have a spare Tektronix 4052 (or 4051) Display Board that I
could buy?
Thanks,
Monty
3 Jul
3 Jul
1:35 p.m.
These systems are rare enough that it's probably worth fixing instead of
treating the board as a simple FRU. There are schematics on bitsavers for
that board, and they are complete.
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.
Does anyone have a spare Tektronix 4052 (or 4051) Display Board that I
could buy?
Thanks,
Monty
--
Ian Finder
(206) 395-MIPS
ian.finder at gmail.com
2:01 p.m.
Is 206 Washington ? I have the remains of a 4051 4052 and 4010 terminal
sitting outside in the scrap pile. Parts have gone to Europe but they're
still pieces left over
They were about 25 miles west of Portland Oregon.
On Tue, Jul 3, 2018, 1:35 PM Ian Finder via cctalk <cctalk at classiccmp.org>
wrote:
These systems are rare enough that it's probably
worth fixing instead of
treating the board as a simple FRU. There are schematics on bitsavers for
that board, and they are complete.
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.
Does anyone have a spare Tektronix 4052 (or 4051) Display Board that I
could buy?
Thanks,
Monty
--
Ian Finder
(206) 395-MIPS
ian.finder at gmail.com
5:59 p.m.
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.
Jon
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.
5:06 p.m.
On 2018-Jul-03, at 1:21 PM, Monty McGraw via cctalk 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.
Does anyone have a spare Tektronix 4052 (or 4051) Display Board that I
could buy?
I take it you are referring to discussion and info from your post on may 27th at:
http://www.vcfed.org/forum/showthread.php?63656-Tektronix-4052-Troubleshoot…
Re a comment in that discussion:
The feedback loop in the op-amp circuitry is the negative-feedback gain-control loop.
If you open that loop the gain will shoot off to -->infinity (in the real world, the
highest the amplifier can do, the output would go binary rail-to-rail).
If you noticing and wondering why the "negative" feedback loops around to the +
input on the op-amp,
it's because the output drivers provide a stage of inversion (specifically Q84/95).
Note there are some mistakes in those Tek schematics around U184A/B. They are mixing up
the pin numbering and +/- input labelling.
There seems to be half-a-dozen variations on the deflection circuitry (was looking also at
the 4051 service manual from bitsavers)
and the error seems to morph around between the versions, like someone tried to fix it at
one point but misunderstood and reintroduced
at another.
On this version you reffed:
https://drive.google.com/file/d/1FQxqfVyOeA1BJjUS7b7X-FzL7Wb8g7q5/view
they get it right.
However, compare to:
https://drive.google.com/file/d/1TJjeZqszca1C7XILsnDyO9D_r64ZMwoo/view
the 2 & 3 pin labels on U184A should be swapped.
On another version on page 96 of the manual they have the +/- flipped on U184B.
Suggestion re the problem:
As you are seeing the oscillation at C196 on the common X/Y bias supply, I would try
looking at Q186, in particular for a B-C short or leakage.
A B-C short/leakage there would be adding C196 to the X output and could be providing the
time constant for the ramp/oscillation.
You could try scoping the B & C of Q186, if the signal and voltage levels there are
similar, consider removing Q186 to resistance check it OOC.
5:16 p.m.
On 2018-Jul-03, at 5:06 PM, Brent Hilpert via cctalk wrote:
However, compare to:
https://drive.google.com/file/d/1TJjeZqszca1C7XILsnDyO9D_r64ZMwoo/view
the 2 & 3 pin labels on U184A should be swapped.
Whoops, correction to my correction, they got the pins right, but the +/- input labelling
should be swapped there.
2364
days inactive
2365
days old
6 comments
5 participants
participants (5)
-
bhilpert＠shaw.ca -
elson＠pico-systems.com -
ian.finder＠gmail.com -
mmcgraw74＠gmail.com -
pete＠petelancashire.com