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On Dec 1, 2018, at 8:51 PM, John Griessen <john@...> wrote:

On 12/1/18 10:11 PM, Gary Robert Bosworth wrote:
My manuals do not list a part number for the viewing hood for any of my 7000 series oscilloscopes.

016-0154-00 is the Batman version -- pictures tomorrow...

I see that you are not getting many replies to this discussion, so you probably don't realize it has been discussed many-many times over the years here on Tekscopes.
A search of the Tekscopes message archive should turn up the actual paint formula for the Tektronix color, from which you might be able to have the paint mixed locally.
I realize the environmental laws are changing quickly around the world, but you may even be able to have this paint put in spray cans where you live.
Shops that supply the paint to automotive body repair businesses might be one place that can help you.
Best of luck!
tom jobe...

On 12/1/2018 5:53 PM, george edmonds via Groups.Io wrote:

Hi All
I also would very much like to source the pain in the UK, ?the blue paint on the ?2XXX series appears to be water based and cannot even be washed with water without if coming off.
73 George G6HIG

???? On Sunday, December 2, 2018 12:25 AM, David Slipper <softfoot@...> wrote:

? Has anyone discovered a source of this paint in the UK ?

Getting it from abroad is tricky because of postal regulations.

Dave

Hi All
I also would very much like to source the pain in the UK, ?the blue paint on the ?2XXX series appears to be water based and cannot even be washed with water without if coming off.
73 George G6HIG

On Sunday, December 2, 2018 12:25 AM, David Slipper <softfoot@...> wrote:

Has anyone discovered a source of this paint in the UK ?

Getting it from abroad is tricky because of postal regulations.

Dave

On Dec 1, 2018, at 8:53 PM, george edmonds via Groups.Io <G6HIG@...> wrote:

Hi All
I also would very much like to source the pain in the UK, the blue paint on the 2XXX series appears to be water based and cannot even be washed with water without if coming off….
Has anyone discovered a source of this paint in the UK ?

-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of
fred@...
Sent: Saturday, December 01, 2018 11:08 AM
To: [email protected]
Subject: [TekScopes] 7854 readout and stored waveform jitter

Hi,

during work, all of the sudden my 7854 started to show jitter of the
readout in the horizontal and vertical directions. In stored mode the
waveform is jittery as well, but in scope mode the waveform is rock
solid. I checked the voltages of the main power-supply and aux supply
plus the 10V reference on the display board are all are fine without
excessive ripple. The amplitude of the jitter is about 1/32".
Somehow I can't believe it is a problem in the digital circuitry, first
I thought the DAC reference voltage had a problem, but its fine.
I love this scope and I use it more frequently than any other.
--
Best regards,

Fred S.

Hi Chris,

Yesterday I looked only at graphs 4 and 5, but I think I read these in the
wrong order (or interchanged the TPs). Hence the purpose of C114 is the
opposite of what I thought, this cap speeds up reverse biasing the gate of
Q546. Today I studied the circuit description in detail (again, after many
years), pages 3-35 to 3-40, and verified waveforms in my 7T11A. Nice exercise.
The memory gate is open when Q546 conducts, so when its base is pulled
negative. For this to happen, *both* gates B and D outputs have to be low. In
rest D is low but B is high. Then when B also goes low the base of Q goes
negative and the memory gate conducts. Some 2-3 us later D goes high, base Q
goes positive and the memory gate closes. Again some us later (end of
hold-off) both B and D switch to the opposite states.
In my 7T11A, low is nearly 0 V and high is 3.7 V (B) and 4.0 V (D). But for
some reason B shows the same overshoot to 4.5 V as shown in graph 4.
With B high and D low base Q was +0.8 V. With B low and D high base Q was +1.0
V. With both B and D low the base was -0.8 V.
The timings were somewhat different from Fig. 3-31 and more consistent with
those in graphs 4 an 5.
I triggered the 7T11A from an SG503 and varied the frequency, in order to
easier recognize the rest period between end of hold-off and next trigger
event.
Hope this helps.

Albert


On Fri, Nov 30, 2018 at 11:13 PM, cmjones01 wrote:

Albert,

Thank you for these ideas. I'll check the relationship between TP106 and

TP109

when I'm back in the office on Monday. The waveform I see at the base of

Q546

is odd: it's a sort of castellated shape with up bits and down bits, but

never

appears to go below ground. I can see what look like those 200ns spikes at

the

anode of CR116, but they're no longer in evidence at the base of Q546. I
should look more closely for them, though, since they'll be clamped to -0.7V
by Q546's B-E junction.

The big anomaly is that the service manual shows waveform 28 at the

collector

of Q546, with 3us-wide pulses heading from -15V to pretty close to 0V. I

can't

get anything like that. The best I have ever seen were similar pulses but

only

from -15V up to about -13V, clearly not enough to do anything useful!

Chris


On Fri, Nov 30, 2018 at 01:14 PM, Albert Otten wrote:

Hi Chris,

The hold-off multivibrator "looks like it's working". Did you check the
waveforms at TPs around U110? The waveform at TP109 should be the inverted
version of that at TP108 as shown in graph 5. (Note that voltage levels at

the

probe tip are 10 times larger than shown in the graph.) But also verify

that

TP106 is already low when TP109 goes low. TP106 low helps to bias the base

of

Q546 in negative direction. What happens to Q546 base voltage when TP106

goes low?

The time constant associated with C114 and surrounding resistors is 0.2 us

or

so. Maybe you missed the short spikes at the base of Q546 for that reason?
Disclaimer: I concluded these things from the diagrams but didn't test it

in

my 7T11.

Albert

On Fri, Nov 30, 2018 at 08:53 PM, cmjones01 wrote:

I had it on an extender in the bench today and established that most of

it is

working: the trigger circuitry, strobe pulse generator and slow scan all

seem

to be doing what they should. However:
- the trace is blanked because the X/sweep output is out of range (it's

at about +15V)

- it seems to be out of range because the horizontal memory isn't

getting any strobe pulses

- the holdoff multivibrator, which generates said pulses, looks like

it's working

- there's a peculiar arrangement of resistors, a diode and a 100pF

capacitor

which takes the outputs of the multivibrator (a 7400 chip) and is

supposed to

switch on a PNP transistor (Q546 I think) which has its emitter tied to

ground

(in equivalent time sampling mode). This is not happening. The

transistor's

base never goes below ground so it never switches on.

Looking at the circuit diagram, I can't see how it's supposed to work. I

don't

have the manual in front of me right now but does anyone know this part

of the

circuit well? My next move is likely to be replacing the 7400 to see if

a

different one somehow magics it in to operation.