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Hi Dave,

I know it seems that simple but I put some internal reinforcement
beams across the top of the bays where the plugins go. I also did one
over the row of controls over that and another L shaped one around the
CRT. I didn't want some impact hitting the cover to have an easy time
bowing the cover in. However, if all you're doing is protecting scope
from dust then you really don't need those. This is why I was so happy
to have a printer that would let me do this in 1 single piece. I kind
of don't want to do a dust cover because then I worry someone might
mistakenly use it to say ship something.

I use most of my scopes too much to worry about dust. The 11801C is a
spare for when the in use one breaks. The 7704A I could probably part
with but I had this problem. It (+ very specific plugin) could have
helped me with +14 years ago which it could have solved.

-Evan

On Tue, Jan 14, 2025 at 12:41?AM Dave Daniel via groups.io
<kc0wjn@...> wrote:

Evan,

Thanks. I have never seen a 7704 so I don't know if a 7704 cover would fit
on a 78xx or 79xx 'scope. I imagine that the only characteristics that
matter would be the outside dimensions of the 'scope bezel and the depth of
the front panel controls.

I'll wait to see what the dimensions of your cover are; at that point I
will be able to decide for myself.

I don't generally have a concern about damaging the front panel controls
but I do wish I had something other than random large plastic bags to keep
dust off of those controls. The same goes for my 547 and 76xx 'scopes.

And, no, I was not expecting you to print covers for me. I can probably
join a local maker shop and print them there.

Thanks.

DaveD
KC0WJN


On Mon, Jan 13, 2025 at 22:13 evan foss via groups.io <evanfoss=
[email protected]> wrote:

Hi Dave,

The 79xx scopes have different geometry on the front panel. The
display is lower down (smart), the power switch is in a slightly less
obvious place, I think the controls might be taller, among many
changes. The 7000 series had a common design style but the geometry of
the front panel and it's layout wasn't very uniform.

It would take a number of thin printouts of the outline to test fit to
make this work or you taking very careful and precise measurements of
some things. Or a 3D scan.

Keep in mind I am not trying to make a business out of this. I just
wanted to share the files and hopefully stop more innocent knobs from
being crunched by accident.

-Evan

On Sun, Jan 12, 2025 at 4:26?AM Dave Daniel via groups.io
<kc0wjn@...> wrote:

Will your 7704A cover fit on 79xx 'scopes? If so, I'd be interested in
having several (4 or 5) of them.

DaveD
KC0WJN


On Sun, Jan 12, 2025 at 00:40 evan foss via groups.io <evanfoss=
[email protected]> wrote:

Hi Folks,

I made a 3D printed cover for the front of my Tek 7704A. I was worried
about accidentally harming the switches while I move it off/on the
shelf. I could clean it up and share it but that would mean a large
reprint to test it and I wanted to gauge interest before wasting that
much plastic and electricity.

PS: I am planning to do one for the 11801 as well. Though I will
probably have to line that with copper tape or something.

Evan

Well, whaddya know. I found this while randomly searching for 2465B problems:



The description of the triggering problem was identical to the one I have... and sure enough, removing the J102 plug made the problem go away. The scope now triggers perfectly. The author of the above article never persued the fix any further, so I might just look into why the TV sync option is causing a problem on my 2465B.

- Keith

Jon,
Just to prevent a possible misunderstanding: I wasn’t talking about the ultor but the white two-part connector somewhere near the middle of the HV lead, where the (usually) red lead enters it.

Personally, I strongly dislike using tape to insulate a cable/wire. With the HV lead, I don’t think shrink tube exists that goes around either side of the lead and shrinks snugly around the lead, without disassembly, that is.

The silicone rubber becomes an integral part of the lead and looks nice because it tapers between lead and connector.

Raymond

Raymond the 21-24 KV CRT Ultor is polyethylene as is,the molded Alden connector.

Indeed any nicks or splitting of the cable will cause arcs or corona to the nearby grounds og the ch?ssis , doghouse cover, etc.

I would try to fix the fault on the cable with heavy duty shrink tube or high grade electric tape.

Jon

I guess something to realize is that an air gap from the HV lead core to the outside of the insulation isn't enough to prevent arcing or even flash over; The dielectric strength of air is far less than that of the lead's rubber insulation.
As an example, I once repaired an arcing cable by filling the area where the (red) lead enters the socket in the middle that runs past the chassis by making a gradual "glove" out of silicone rubber from the cable to the white socket. And yes, everything was clean but arcing slightly before that!

Raymond

Cross posting from Equipment For Sale group


Clean insde & out.
The selenium stack was open, I bridged it with 3A rated diodes. The variac had open windings, I replaced it with a corrrect one. Prior to me the front panel CB was replaced with a fuse holder. I replaced the handles. Otherwise stock.
I ran through the calibration and most adjustments were spot on.
The one picture shows the tracing of a 2N2369.
There is some warmup drift, and the intensity doesn't seem as bright as I would expect. Not sure if this is a HV transformer issue or ?
$250 includes manual (w/122C mod info) and cart.
Local pickup preferred, I'm located in Waukesha WI 53188.

Cross posting this from the Equipment For Sale group


Clean inside and out.
Serial #s 577: B108477, 177: B059426
Option 10 is a 10 x 10 cm display with an extra cm L & R edges.
Storage works, upper & lower. I did an "Etch-A-Sketch" in storage mode with the H & V position controls, see picture.
I have not run through a calibration.
Collector Supply knob is cracked.
Display is a tracing of a 2N2369.
Transistor fixture is not included.
$550, includes 577 & 177 manuals (with Option 10 info) and cart.
Local pickup preferred, I'm in Waukesha WI 53188. I can ship but will need a firm purchase commitment and time to construct a box. Shipping will be expensive!

It affects all channels in the same way. Hence the thought that it's maybe an issue with U500?

Keith

Rebonjour

Does the trigger issue, affect all 4 ch and line or only certain channels?

Trigger path is from vert amps and multiplex IC.

Use the self test, one og the tests or exer is for trigger.

See trigger debug flow chart in service manual

Bon chance

Jon

Hello, I had a similar crackling and hissing problem with my 7904 years ago. It turned out to be the voltage multiplier U1615, internal arcing. The only visible indication of something being wrong was the burned resistor R1604, 13ohm. After replacement the scope was working again.
G?ran

Thanks for the reply Jon,
The nick on the HV cable is about half way along from the dog hole to the connector, visible on the third image.
If I don't need to mess with the transformer I won't, it's just that I'm really keen not to have to reassemble and find the thing is still crackling because I didn't do all that I could when the PSU was apart!

Merci Jean-Paul

Probing the TGA signal from pin 18 of U500, the triggering waveform there is as I see it on the screen i.e. intermittent. So it looks like U500 or circuitry before it in the trigger path is faulty.Time to read the theory of operation of the trigger circuitry I guess.

Something is borderline as triggering is OK at slow sweep speeds but not at < 1ms/cm.

Keith

Thanks for your suggestion, today I received a secondhand 80e02 in good condition for an acceptable price ?

Keith bravo for your work on NV Ram, beware of Chinese knock-off and old date code parts.

Use machine pin socket

Full cal is needed after RAM replacement

See service manual and proper test equipment

Can be hours or days first time.

Trigger issues described may be marginal trigger hybrid U400, or symptoms of damaged A5 control board due to SMD lytic corrosion

Beware of hidden damages in A5 visa, parts or inner layers.

Corrosive liquid and gas of the SMD lytic flow over the board, even if caps look OK

Tell tale is dull, green pads or joints, near the DAC ref area on A5, controls jumpy or intermittent

Every SMD lytic needs replacement.

Every nearby component and trace is suspected

Bon chance

Jon

Hello again

Last two photos show Carbon and dirt accumulation on HV box , cables and Kapton film insulation

Needs through cleaning with 99% isopropyl alcohol.

Where is the HV cable nick, photo seems fine.

DO not fool with the HV transformer.

Very easy to damaged and costly to replace

Reassemble carefully, and test after cleaning

Jon

Hello Keith,
I also have trigger problems with my 2465B. The SRAM Dallas has already been replaced and refilled because of the old Li battery. Because the Scope also had (and still has) the error message "TEST 05 FAIL 42" I had the board 05 examined by a Tek professional - without success. Visually, I cannot detect any corroded or burned components.

Greetings JuHe

Hi all,

I had some time so dug into the PSU a bit, swapped ot the last tantalum in there, and upgraded the aluminium 'lytics as per revisions list in the manual. The big storage caps I ran up to 195V for half an hour and checked for leakage, it was 10uA on one and 20uA on the other, they measure at 980uF and 1025uF, they seem absolutely fine to me.

The HV box showed carbon or soot near the dog house hole and a mark on the insulating washer that wraps around that hole. There was also quite a bit of carbon/soot around the small hole in the aluminium case that could have been conductive? There is also a nick on the HV cable which doesn't go through the insulation, I could see no light near that nick when the PSU was working and crackling. So saying, I have no experience of coronas and arcs, and little of these kinds of voltages, so I have added some photos at the following link titled 7904 PSU crackling noise:

/g/TekScopes/album?id=300059

I have cleaned the box thoroughly and there was no evidence of any damage to anything caused by any arcing, nor is the mark on the washer still visible, but I don't know if there would be visible damage? There were also some light carbon deposits on the large ceramic caps. Is this a cause for concern? The little piece of loose insulation visible is (I think) probably a result of my bending the caps out of the way to get at the transformer wires to unsolder them. Please advise what you think? Might I have found the smoking gun by any lucky chance?

Finally, the transformer which I expressed concern about is at last exposed. It doesn't look too bad to me, not blackened or anything, and no more filthy than most of the rest of the unit. The core is quite loose on the windings but there isn't anything obviously amiss to my untrained eye. Whilst the thing is apart, are there any useful tests I can carry out on the trafo to ascertain if the crackling might have been coming from it or is it rather unlikely that this might be the case?

Many thanks for any and all pointers as always!

So I desoldered the DS1225 nvram carefully and fitted a 28 pin DIL socket.
Took the nvram and just to see if there was still any life in it I programmed it using a TL866ii programmer, using a .bin file from the EEVblog thread.

With the nvram replaced, the scope booted up without any errors. Now this was just a temporary test until I get a known good DS1225AD from Mouser, but at least it proves that the original cal data was bad ;) And the readout does not have the question marks anymore, hurray.

The remaining issue is the triggering. The symptoms are:
- scope triggers in auto lvl / auto mode with sweep speeds longer than 2mS. At 1mS it triggers most of the time, but not all, with faster timebase speed it gets more and more intermittent and at 500uS or so it stops triggering. This is with Y input at 200mV/cm and probe on the cal point (400mV p/p).
- the display is OK, everything reading as expected there.

Before I start going through sweep troubleshooting, has anyone seen a trigger issue like this?

Keith

Very useful. Let me have a rummage and see if I can find any of the 3 units mentioned.

I agree the LM1881 ads nothing here, indeed already tried it

--
Christopher Hilton-Johnson
The Stone Barn
Cottisford
Oxfordshire
NN13 5SW

07831 458867

The original posting refers to the signal as RGBHV. All five components are already separated. As much as I like the LM1881, there is no need for it (i.e. sync separator) in this application.

To trigger on sync event number 270 or any other event, I recommend triggering the timebase after Delay-by-Events. If you can borrow a 7D10 or 7D11, you can either run after or trigger after the 270th event is counted. The DD501 can also provide the event delay function.

You might be able to use a standard delaying timebase, but the delay jitter might make it difficult to select the event to trigger the delayed timebase.