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I have one of those. Real work of art.


Peter

opt.78 Looks perfekt with a smoke filter from Tek,

see

greetings

Martin








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So who grabbed the really nice deal on the 7844 OPT 78 that just sold on
eBay? Hope it was one of y'all!
Nathan KK4REY

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Optimized the layout to increase ground planes. Determined fixed resistor 'calibration' values that work within the LM358 offset spec. Retuned the ref diode schottky input network as I am using different detectors. Used a 18 AWG enamelled wire 1.5cm long to feed the BNC output direct from the PCB. Established rigid 'coax' shield coverage for this 18 AWG signal wire. Established rigid 'coax' shielding for the input as well via the BNC PCB mount grounded to dual ground planes.

Keep looking for corrosion damage like a component connection or opened run, or remaining crud (especially on/between IC leads) that you may have missed. An old toothbrush is good for scrubbing. It's best to wash the board again after removing the old caps, before putting in the new ones. Also, double check the polarities to be sure none are backwards.

I went through the same thing a while back - fortunately, it worked after thorough washing and scrubbing. I have stripped all the old Al SMT caps but not yet installed the replacement Ta ones - it works as-is, even without them.

Ed

No;) I didn't grab it, was asking who... Hoping it was somebody here... I was still trying to

convince the

"finance committee". I do have an eBay search set for Tektronix Opt 78... Just think the blue is

cool.

Nathan KK4REY

The blue is surprisingly hard to look at. The eye does not focus particularly well on it, and the
eye is less sensitive to blue as compared with regular green phosphor - so fast signals are
significantly fainter (to the eye) with blue. It was intended for photographic attachments, since
the polaroid film used was more sensitive to blue (as compared with green).

I have a 7904 with a reduced scan CRT and blue phosphor for those wanting the ultimate in
photographic writing speed - but it is impossible to look at for any length of time! I keep it as a
rare curiosity.

Craig

He, he, Sigur?ur ?sgeirsson. Agreed! :-)


Qservice indeed shipped to Montreal, Canada. I got even a printout of 7854 service manual from Dino (Qservice).


Which part of Canada are you in, Snapdiode?

Hi Alex,

You may have luck by visual inspection for bad components. I prefer a more systematic approach.
You didn' t mention whether or not you have another scope to do measurements in th 545A?
In the A generator schematic C180 + switch is shown in a dashed box, merely as "placeholder" for the actual set of hold-off capacitors (shown at A Timing Switch schematic).
There is no indication that the A sweep "hangs". It might well be that the sweep circuits are at rest and are waiting for a trigger signal which never comes. I mean, the fault could be in the trigger circuits. (The troubleshooting text assumes that the trigger circuits are properly free running while the sweep circuits don' t respond to that.)
I would first try to correct the B sweep since there the fault is not in the trigger circuits sine you have at least something like a trace. You never mentioned the effect of the front panel B Sweep Length knob (note that time base A only has an internal sweep length adjustment). B sweep length can be reduced to about 4 cm, that' s roughly what you have. B sweep has no front panel output like the A sweep, but you can safely measure the sweep signal at the kathode of V283B. If you don' t have a scope for that, then simply use a DMM while you set the speed very slow at 5 s/cm. If the amplitude is correct (some 150 V peak-peak) then the fault is somewhere later on, either in the horizontal display switch or in the horizontal amplifier.
You showed 2 pictures with reference to time base A. Maybe you meant a channel of the vertical plugin (since time base A didn't work at all)? The second picture probably shows high frequency oscillation somewhere. But leave that for later...
BTW did you already rotate all switches and pots many(!) times through there ranges?

Albert

No;) I didn't grab it, was asking who... Hoping it was somebody here... I
was still trying to convince the "finance committee". I do have an eBay
search set for Tektronix Opt 78... Just think the blue is cool.
Nathan KK4REY

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[]
On Wed, Mar 23, 2016 at 15:37, Craig Sawyers' c.sawyers@...
[TekScopes] <TekScopes@...> wrote:
> So who grabbed the really nice deal on the 7844 OPT 78 that just sold on
eBay?

They are a good and unique capability scope. Looks like some cosmetic
things need sorting out, and
I hope that it arrives OK and without damage.

I bought mine 3 years ago for the same sort of price in the UK (40), and
like yours it has a blue
phosphor CRT.

Let us know how it goes

Crai




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So who grabbed the really nice deal on the 7844 OPT 78 that just sold on eBay?

They are a good and unique capability scope. Looks like some cosmetic things need sorting out, and
I hope that it arrives OK and without damage.

I bought mine 3 years ago for the same sort of price in the UK (?40), and like yours it has a blue
phosphor CRT.

Let us know how it goes

Crai

I've used qservice in the past without trouble. I'm in Montreal, which
although in Quebec, still remains part of Canada. Maybe you can email them
to work out postage?

On Wed, Mar 23, 2016, 07:05 snapdiode@... [TekScopes] <
TekScopes@...> wrote:

Thanks but they don't ship to Canada.

Sorry, I did not realize you were in Canada -- I went and searched for
shipping in the US. If you are near the border you could get it shipped
to one of those drop-box places or a friend for around $5 or $6. But
it's a pain with our 75? Canuk buck and outrageous shipping charges.

So some CDN alternatives: you can get Permapoxy Plastic Bonder at Crappy
Tire. It is a similar chemical but I've never personally tried it or the
JB Weld version on nylon. I did a test one time and found the Permapoxy
to be a stronger bond than JB Weld Plastic Bonder (Crappy Tire or Home
Hardware) on acrylic. All the above are around CDN $10 plus tax.

Comparing the literature, Locktite Plastic Bonder specifically mentions
nylon and the MSDS shows it is methacrylate based. Auto parts stores
are most likely to carry it, or CDN$20 shipped via Amazon.ca. (Looking
up the MSDS, I just discovered that Locktite also makes a cyanoacrylate
based product called "Plastics Bonding System" that they claim will work
on Teflon)

So who grabbed the really nice deal on the 7844 OPT 78 that just sold on
eBay? Hope it was one of y'all!
Nathan KK4REY

Sent using CloudMagic Email
[]

Do you know where I can buy 16 space suits?

Oh and I had a moment of sanity and remembered that ty-raps are made of Nylon. Doesn't melt at the same temperature as the pot so I'm back to believing they're Delrin.

Hi Ancel,

I'm curious what change(s) did you make?

And do have a suggestion as to what might cause what you're seeing?

Cheers
Dave

On 03/23/2016 12:15 AM, snapdiode@... [TekScopes] wrote:

Sounds good but at 45$ for 47mL it's eating into my scotch budget...

A man has to have his priorities.

Mark

Thanks but they don't ship to Canada.

Because it's probably just as cracked as the three other ones I already have.

I am not sure what kind of capacitor that is. The oil-paper ones I am
familiar with use a hard Bakelite case.

And if that capacitor is C165, I do not think it can cause this
problem. What the manual is describing is the sweep terminating early
do to a problem around or after V183A.

What is suppose to happen is that the sweep ends once it reaches a
certain voltage level which is apparently not happening. The manual
is suggesting that the circuit which detects the proper voltage level
is triggering early.

Hello all,

I have been a group member for a while although not an active one, I recently bought a TDS 544A and TDS 540 cheapish.

Work has started on the 544A it used to:
FAIL++Acq/Proc Intf,
FAIL++Acquisition,
FAIL++Attn/Acq Intf.

The Acquisition board has been recapped, dish-washed and scrubbed down twice with a mildly basic soap (pH 8.1), corrosion was quite severe around the "time interpolator and jitter ramp" section, many cut traces.

Now I get:
FAIL++Acquisition

It will not pass SPC either, failing on signal path.
The most recent error logs are:

(For POST) ERROR diagnostic test failure
ctlConfidenceDiag 2.50e-9<=exp<=1.20e-8 actual 1-something

(For SPC) ERROR 2260 Calibration failed
Repet Cal Failed




The scope is otherwise working quite well, not too far off cal, CH1 is slightly out, CH1 & CH4 are slightly noisier than CH2 & CH3 even when grounded.


I do not have GPIB to access the full error messages.


Any clues on what could be causing those errors are welcome.


Paul