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The LCD display on these are miserable.. An early electroluminescent backlight with a heater for cold environments, difficult to read in almost any condition. If the display is bad, ie, looks like it has a dark spot, it's gone. There were a few "improved" versions of the display assembly.
The input sampler on this model is a hybrid, not repairable, and impossible to find.
The chart recorder has a roller that turns to molasses, making a huge sticky mess.

When working they are fine, save the lousy display.

Unknown, but I suspect (don’t really know) that the tunnel diodes are broke. Most of the earlier 1502’s that we sent to customers on rent came back with blown diodes

Regards,

Stephen Hanselman
Datagate Systems, LLC
3107 North Deer Run Road #24
Carson City, Nevada, 89701
(775) 882-5117 office
(775) 720-6020 mobile
s.hanselman@...
www.datagatesystems.com
a Service Disabled, Veteran Owned Small Business
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There are a slew of them on eBay for pretty nominal prices as parts units. How hard are they to repair?

On Fri, 19 Apr 2019 19:30:06 +0000 (UTC), you wrote:

My SD-26 heads came with shorting caps. And I need caps for my SD-22 heads. I'm wondering though if non-shorting caps would be more appropriate. The male pin rotating in the female sleeve seems as if it presents a wear issue. And a non-shorting cap should protect the input diodes from ESD just as well.

The label on the head says to use a 015-1020-00 for shipping which according to Test Equipment Depot and TekWiki is an SMA male shorting plug.

Non-shorting Amphenol caps are $1.85 each from Digikey and shorting are $3.46 each in quantity of 25.

Comments?

No reason you couldn't use a termination for the same thing, unless
you think that a static discharge across a 50 ohm termination might be
a problem.

Harvey

Thanks,
Reg

Hi Albert,

W.r.t. sensitivity for DC input (did you try?) I forgot that the setting

of S901 "Correction Memory Switch", see page 2-5, is important. For now the
best way is to set the switch in the rear (OFF) position (as long as you
don't have a pulse generator head).

Explanation of S901 purpose is quite vague in 7S12 manual, I did try all 3
positions and there is no change. Btw I also fed the head with very low
freq sine wave thus simulating DC input, and still no go.

With a DMM attached to the front panel Vertical Out connector you can see

that Memory is slowly drifting.... the DMM reading will immediately jump
back to the normal value. The trace should reappear immediately at the
previous vertical position.

Yes, the drift is very very slow. I'd say it would tale a whole minute for
it to cross 1 div, with the settings I used. When I switch free running
back on, it immediately jumps back to its old position.

The heads have different connectors, SMA and BNC, and your signal

generator perhaps one of these. You need a power divider or a splitter or a
T and at least an adapter to from one type connector to another. All these
things could introduce faults. Are you 100% sure that the sine wave signal
arrives "inside" the S-4?

Yes, I'm using BNC-SMA adapters and BNC T adapters. I can definitely
measure 50Ohm (52 to be exact) at the point where I'm inserting the signal,
so I guess that's the best I can tell that I'm feeding the signal to S-4.

Even though this feedback-offset loop seems to be working, I decided to
check the head internally, namely the gate bias. It is possible to adjust
R32 according to manual, and its position falls around midpoint. However I
found the gate bias to be somewhat asymmetric, it's all part of a feedback
loop so it's hard to tell what causes it. The voltages on the S-4 internal
preamp board points are:
- C (feedback): -337mV (500mV/div), -146mV (200mV/div), -79mV
(100mV/div)...and reducing geometrically while increasing mV/div
- M=1.93V, H=-2.29V, V (at 100mV/div - I kept this setting because of the
relatively small feedback voltage on C, also applies to measurements below)
- Voltage across D20=405mV, D23=412mV, D25=424mV, D28=422mV
- on Q36 Vg= approx. -1.80V, Vs=-1.76V, so Vgs seems to be slightly
positive (can't measure directly between gate and ground as this point is
very sensitive)

I can't say if this slight asymmetry can be a problem. Preamp output (point
E) shows sampling pulses, but zero reaction to my low freq sine wave input
signal. I still cannot say whether the snap-diode circuit works, is there
any test I could do to verify if it's working? (E.g. are the sampling
spikes observed on point E due to snap-off working, or are these coming
through the feedback line?)

Best Regards, Nenad

On the right side: loosen two setscrews in the top and bottom rails just behind the front panel.
One the left side: loosen a small setscrew on the top of the lower rail. It holds the left module pivot in place. Remove two Philips flathead screws on top of the upper rail. These are the same ones you take out to pivot the left module out. Do not remove the left module screws at the rear of the plug-in.
Unplug the calibrator output cable from behind the front panel connector. Work the front panel connectors off of the internal circuit boards. That should be all it takes. The 3 pins that were held by the setscrews should slide out easily. They are the only mechanical connection to the rest of the unit. The pots at the lower right of the front panel are on a separate internal bracket and the knobs pass through the front panel without being removed.

Reassembly: Do not tighten the lower left setscrew to the point that it interferes with pivoting the left module out. It's not necessary. Be gentle with the two right side pins. They are plastic and can be broken. They can even be cut in two by overtightening the setscrews. If you end up with one of these pins to spare and in good condition, I need one for my 7L5.

Regards, Cliff Carrie
________________________________
From: [email protected] <[email protected]> on behalf of Ed Breya via Groups.Io <edbreya@...>
Sent: Friday, April 19, 2019 2:38 PM
To: [email protected]
Subject: Re: [TekScopes] 7L5 knob removal

OK. I found screws from the inside, but they are inaccessible without pulling the right side RF casting assembly. It also appears the front of the casting is held with setscrews on some kind of pins in the front panel, rather that the usual screws hidden under the faceplate, that I expected. This must be how they managed to assemble everything from behind. It's gonna be a lot of stuff to pull apart.

Ed

My SD-26 heads came with shorting caps. And I need caps for my SD-22 heads. I'm wondering though if non-shorting caps would be more appropriate. The male pin rotating in the female sleeve seems as if it presents a wear issue. And a non-shorting cap should protect the input diodes from ESD just as well.

The label on the head says to use a 015-1020-00 for shipping which according to Test Equipment Depot and TekWiki is an SMA male shorting plug.

Non-shorting Amphenol caps are $1.85 each from Digikey and shorting are $3.46 each in quantity of 25.

Comments?

Thanks,
Reg

Thanks Cliff. Before seeing your post, I figured out that the whole front comes off - the hard way. I started unscrewing everything front and back, and whole plug-in began to fall apart. It's pretty slick they way they did it. I have often had to take front panels apart, and always dreaded removing everything on the panel in order to pop the front plate just to access the rail screws. The 7L5 assembly is fairly complicated, but it works. I now have the front panel assembly separated, and the special switches removed.

Fortunately, these switches, the rotary encoder, and other items up front survived in good shape, especially considering what must have happened to this poor thing. It appears it was probably in a mainframe that got dropped or hit with a forklift from the back, deforming it such that the plug-in is severely distorted. The depth is off-square by almost a cm side to side. The guts seem to be intact, although all misaligned, and the front panel casting and face are bent, but otherwise not a scratch on it. The only damage up front was a broken small knob and bent shaft on the dot frequency fine tune. The back plate is mangled up, but should be fairly easy to straighten back out.

I'm hoping that I can just strip the front panel and straighten the pieces, straighten the back plate, and replace one or both busted plastic board edge connector supports to get it mechanically square again. The rest should be about realigning the guts and figuring out how to put everything back together. After all this, I can then plug it into a mainframe and see if it even works.

I have to mention again, that I like this pinned assembly method used here. It probably saved this plug-in from nearly certain destruction. If the front was held on the rails with the typical screwed-on method, the casting would have likely snapped and taken out the special switches, and more. With the pins, everything still bent, but the pins pulled loose, allowing some give on the assemblies, without fractures. Actually, there is one other broken item - one of the plastic pins from the front panel snapped, and the end is probably still in the side casting. I'll be able to rig up a simple replacement for the pin.

Ed

On Thu, Apr 18, 2019 at 08:15 PM, Leon Robinson wrote:

Take a few pictures

Along with picture, I use a sharpie, and mark the parts on the inside... where it isn't visible. I use 1A, 2A... and so on, for the left... and 2A, 2B...and so on for the right. I also mark the part, and where the part was attached.

On Thu, Apr 18, 2019 at 04:01 PM, John Griessen wrote:

advise on the tools

along with the tools above, I'd take an adjustable wrench, a socket set (with ratchet, and drivers)… and a set of deep sockets, for removing recessed bolts.

On Thu, Apr 18, 2019 at 05:04 PM, Dennis Tillman W7PF wrote:

there are two VERY UNUSUAL screws that the top shelf pivots on.
Those have to be removed with care.

Hi All: If I remember... and it is the hex bolts/screws, in the pivot.. that are recessed... I used a ratchet and a socket, from a set of "deep sockets" to remove those. It's straight forward with that kind of socket... I found a regular socket didn't have the reach... but, you might be able to carefully extract the bolt, using a socket, from a regular socket set.

Also I posted to a couple other threads, on the topics of scope cart disassembly.

Regards all.

OK. I found screws from the inside, but they are inaccessible without pulling the right side RF casting assembly. It also appears the front of the casting is held with setscrews on some kind of pins in the front panel, rather that the usual screws hidden under the faceplate, that I expected. This must be how they managed to assemble everything from behind. It's gonna be a lot of stuff to pull apart.

Ed

Ed,
Be careful with those knobs. The switching (partly physical contacts and partly an optical encoder) is contained entirely inside the knobs themselves. Disassembly is not recommended unless they have a specific problem, although I did it successfully to relubricate them.
Follow the manual procedure for removing the front panel as a unit (not so obvious, but not too difficult). The knobs are attached by screws installed from the rear of the front panel. They have pins that plug into the front panel circuit board. I did this some time ago, so I would need a close look at my unit and the manual to give you more detail.
Regards, Cliff Carrie
________________________________
From: [email protected] <[email protected]> on behalf of Ed Breya via Groups.Io <edbreya@...>
Sent: Friday, April 19, 2019 2:10 PM
To: [email protected]
Subject: [TekScopes] 7L5 knob removal

I just picked up a severely mechanically damaged 7L5, and trying to rebuild it. I started taking apart the front panel, removing the knobs as usual. The frequency span/resolution and time/div knobs have no setscrews, and appear attached somehow from inside and behind the front panel. I peeled off the black knob face covers too, hoping to find some attachment hardware, but they're blank underneath. Does anyone know the trick to removing these knobs? I R'dTFM but didn't find any explanation, and it's not clear at all from the mechanical diagrams.

Ed

I just picked up a severely mechanically damaged 7L5, and trying to rebuild it. I started taking apart the front panel, removing the knobs as usual. The frequency span/resolution and time/div knobs have no setscrews, and appear attached somehow from inside and behind the front panel. I peeled off the black knob face covers too, hoping to find some attachment hardware, but they're blank underneath. Does anyone know the trick to removing these knobs? I R'dTFM but didn't find any explanation, and it's not clear at all from the mechanical diagrams.

Ed

What more would you like to know?

The limitation with the 2402 is simply its age. The hardware is well made so, that aspect of the age is not a big issue. But DOS is a problem. MANY modern interfaces assume that you have some version of Windows later than W98.

It was very difficult to find the national instruments GPIB driver and C programming library for DOS. Even national instruments itself doesn't know what drivers to use for the GPIB board that was distributed with the 2402. I eventually got it. Another difficulty then was a C compiler suitable for DOS. I ended up using Turbo-C 3.0. I had used that program (version 2) back in the day, but I forgot/didn't realize how much C (not even C++) has changed with the C99 and later standardizations. It was a little difficult to rearrange my brain to suit the early C language!

This entire project was very interesting BECAUSE this hardware was used as the foundation for several different standards (PC-104 for the video and EBX for the mobo). But they do not follow the exact standard that was devised subsequently!

I think that it is very worthwhile to upgrade the motherboard to the Versalogic VSBC2. It is a drop-in replacement physically. and I only needed to modify the connectors on the serial ports (two 2x10, to one 2x20), and the PCB to mirror the PC-104 connections for the ISA bus header, and a power supply for the mobo.

But after that inconvenience you get a lot more RAM, and more speed, and 486 instruction set with math coprocessor. This HW is completely capable of running windows 98, which will still allow 16-bit DOS programs to run fine (usually). I am using DOS 6.33 and not windows.

If you wanted to keep the 286 motherboard, then you pretty much need to stay with DOS, which is not a big problem at all. 1M of total memory is quite sufficient for most purposes in the usage of the 2402A. I simply liked the challenge of making what I call a 2402 "B". Or maybe it should be called the "C" version. The "B" version could have been a 386 CPU. and a 486/586 might have been the "C" version!

Let me know what more info you would like and I will help out any way I can

-Tony

Tony,
Count me in as "very interested". I recently acquired a 2402A with FDD/HDD and it looks like I'm going to have to replace/reload the hard drive. Thoughts were to use this as a scope controller, general purpose GPIB master and as a driver for the two parallel-port-interfaced PROM programmers here in the lab...but I'm open to suggestions on additional functionality.
73 - Fred, N8YX

Hi
Your problem is that in the UK where prices are higher than in the US at amateur radio rallies a 7633 with two or three plugins sell for under $50
73 George G6HIG

On 4/18/19 8:59 PM, John Griessen wrote:

Needs help.
At least it's nice and bright!? Probably no HV trouble, just LV debugging to do...
$80 shipped w/o plugins

No response. Ah well, high shipping prices mean disassembly for this poor tired broken scope.

I recently bought one of these and I was able to get it into the back of a VW Golf cabriolet, even with the soft-top up. Indeed, the ability to open the roof of the soft-top was an advantage in getting the thing in! The main tilting shelf was adjusted to horizontal and the cart went in with its rear on the two rear seats, such that its narrow dimension was fore-and-aft in the back seats.

Be aware that all Model 3 carts are not the same. Some don't have the framework and lower shelf, some have one lower shelf and some have two lower shelves. The bits and pieces that screw onto these lower shelves for the mounting of other scopes or TM500-series stuff are handy, too. If you get any of the mounting-straps, consider yourself lucky.

Best of luck, Colin.

On Thu, Apr 18, 2019 at 10:00 PM, Raymond Domp Frank wrote:

Hi Sean,
Glad that's solved.

I assumed that it should work just like compensating a passive 10x probe.

You have to realize that the compensation C of Hi-Z passive probes compensates
for the cable and termination C at the 'scope that the probe tip "sees".
The circuit in the head of the FET probe effectively isolates the
(low-impedance) cable from the tip.
Have fun with your P6201 and don't forget it is vulnerable to damage from
static and higher input voltages, see the manual. Only use it without
attenuator when necessary.

Thanks for the explanation and correcting my flawed assumption. I was aware that it is very sensitive, so I've been extra careful and will continue to me. It's a great tool to have. I've noticed it is highly sensitive to RF. I have an experiment on my bench with a 100 MHz clock coming out of an FPGA into my logic analyzer for state analysis and the P6201 is picking up the 100 MHz signal on top of the calibrator signal of the 2465B.

Sean