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Here is a parts scope I got from eBay /g/TekScopes/album?id=257163

Most of the knobs are smashed, it's been spattered in something gray that won't come off with soap or IPA, but when I powered it up it appears to be in almost perfect working condition (I say "almost" because I didn't really try to test it in any complete way, just fed the cal signal into both channels, twiddled what knobs could be twiddled, and tried the different button positions. Everything I tried seemed to be working perfectly).

I'd like to turn this from a parts scope into a second bench scope, but I'll need to completely replace the front panel and knobs, unless I can find a way to clean them up. Whatever is spattered all over it won't wash off with either detergent and water or IPA, and I haven't tried any stronger solvents or vigorous brushing. Any advice on how to clean the front panel and remaining knobs, techniques or safe solvents, would be appreciated.

-- Jeff Dutky

Awfully high price for an "ornament"; and you'd need quite a substantial Christmas tree to hang that from!
-Dave

Just saw this on ebay in the UK :

Looks like it's been stored in a tropical jungle for a few years!

Anyone got any worse examples?

I checked my working scope this morning. I wish we could do inline pictures. I reviewed my tear down pictures and found that I had a shot of the DTP knob before I took it off, and am 99% certain that it's in the full ccw position. The new (parts) one is SN 29XXXX, the "old" working one is 31XXXX. The 29XXXX is at 0.35, the 31XXXX is at 0.25. Interestingly the 29XXXX has the fine dial setscrew at the "1" position. The 31XXXX has the setscrew at the "3.5" position. That's funky, but not really relevant?

I also wonder about the history behind these "min" settings. There's got to be some engineering behind it.

I don't recall them being non-zero back in my Army days. My experience, in general, is that there's not a lot of use for the B-delayed trigger. Perhaps more so in broadcast TV? (As another aside: in my profile picture I'm using the B-delayed function to examine a GHz radar transmit pulse triggered from a 20kHz system clock. Funny the things you remember). In any case, I don't recall the zero or values on the knob were of any interest. It was just a device to move the B-delayed signal under examination. This could be entirely my experience and use case only. I would be interested in learning what use cases in which values from this pot are needed.

Is this style of multi-turn pot just a means of obtaining fine delay control over a very large range? The ability to have nano-second resolution over a micro-second (or mili-second?) range. 1000-1 is a pretty large range.

Also interestingly, the other scope visible in my profile pic is a Tek 491 spectrum analyzer. I recall that it had a crank-knob on it. I was reviewing replacement knobs on the sphere site and came across that knob and all these memories came flooding back. I remember cranking on that thing to slew the spectrum analyzer across several orders of magnitude of frequency. So I wonder if these are just devices for handling fine control over a large range.

Dave

Colin,

Oh, I had expected some kind of calibration process, but it's just a bunch of constant offsets for different models.

I see that I am lucky to only be concerned with a model that is always set to 0.0 (the 475 and 475A). Good to know, however, since I would surely have been led astray on my 2215.

Thanks

-- Jeff Dutky

I've gotten it occasionally. I usually go there from what Firefox calls a private browsing window. Cookies aren't saved there and the first time going after restarting the browser is when I would get it, if I get it. Like I said, it's occasional.

Vince - K8ZW.

--
K8ZW

Weird. I NEVER have a Captcha / Not A Robot screen or button when using PayPal....

I do not save my password. Have to enter it every time, my choice. Works for me.

I do not understand the "how far along in the buying process you are" comment. All the screens on PayPal seem logical to me. And there are not many when sending money, either on their website only or through a vendor link to send funds.

So far it works well for me! Both as buyer and sending money to friends. Even for Tek supplies, to keep it on subject.?

Frank DuVal

Hello to all,

I should have many 3A1/3A6 and other 56x series plugins in my stock.? The problem is they are on the other side of Ohio at my other house.
Let me know what you want and I can look for them in a few weeks. Figure $20-$40 range plus shipping for most.? They will be complete (and most were tested/working years ago), but as-is now.

I also have many letter and 1xx series plugins.

You can email me direct at: jreese7010@...

or phone: 740-947-7103

Regards,

Jim

Jim Reese
Waverly, OH

Thanks for the guidance,

I suppose I have to take the cleaning challenge first as there are couple of suggestions for it.
As I didn't get any signal to R130...

I am also getting another unit to facilitate part swapping.

Regards,

Jouko

Bob,

Where are you located? there is a small handheld Tektronix scope in a
surpus store near me and that I can probably get cheaply. As best as I can
remember it is a 2xx model but I don't remember the complete model number.

On Wed, Nov 25, 2020 at 10:09 PM greenboxmaven via groups.io <ka2ivy=
[email protected]> wrote:

My main pleasure with equipment is finding inoperative or basket cases
and restoring them. I just finished a 2230 and an R-631B. This is an
account of the projects, skip now if you aren't interested.

The R361B was obtained from a member of this group, and I was quite
pleased with it when it arrived. I replaced the power cord, and tried it
out. It came alive, had a trace, then a loud snap was heard and it went
dead. I feared the worst, but continued with the work. It needed a bath,
and got it, followed by about ten hours in a hot box to dry it out. I
wanted to see if I could get the power supply working before I put the
jug back in after the cleanup. First tests were aweful. None of the
voltages were correct. The negative 100 volt supply is the reference for
everything else, and it was producing about 115 volts. All of the others
were very low. After a few hours of round and round circuit tracing, I
found the key problem- a partially shorted ceramic condenser. It was one
of the square red Erie brand ones, rated at 200 volts. There were two on
the board, I replaced them with 600 volt ceramic discs. There were two
other old electrolytics, I changed them out as well. The fuse protecting
the high voltage supply was gently blown, not fried and flashed all over
the glass tube. After finding and replacing two fried transistors in the
positive 125 volt supply, everything came alive and right on what they
should have been. I put a fuse in the high voltage supply, it came alive
with an output nearly 4KV, it should have been 3300. I turned the HV
adjustment all the way down, but could not get it below 3500. Both of
the transistors in the HV regulator are "special selected", and tested
good. After studying the manual, and not having exact original
transistors, I added a 12 meg resistor in parallel with the 2.2 meg
resisator coming from the moving contavt on the HV adjust pot. That
allowed me to adjust down to 3300 volts. I cleaned all the switches and
pots in both the mainframe and plug ins, re-installed the jug, and tried
it out. With adjustment of the sweep and position controls, I was
rewarded with a good bright trace. External signals and the built in
calibrator were displayed quite well. The vertical plug in I have is a
single trace differential, not especially useful to me, so I have a 72
dual trace on order. I will let the scope cook on the bench for another
day or so before I put it aside waiting for the dual trace preamp to
arrive. It will probably be used in my RTTY setup, the vertical response
is only about 600 KC.

The 2230 was a genuine basket case, almost entirely dismantled and
filthy with carbon dust. It was a freebee with another purchase at the
Rochester hamfest. I was quite skeptical until I got it home and found
that except for many screws, it was complete. It wasn't stored in the
dirt, it was operated in the filth because the knobs and front panel
were almost unreadable, and the focus pot was completely covered in
fuzz. Getting the front panel and control label plastic sheet off took a
bit of exploration, but WD-40 and a blow dryer softened up the adhesive
on the sheet, and it came off with very little damage. Now I could
remove the front panel to give it the cleaning it needed. Now fully
dismantled, everything got a bath. The cleaner and rinse water were
black as night, but everything cleaned up very well. After re-assembly,
cleaning and lubing switches and pots, it was time to see if it would
come alive. Turning the power on did nothing for a second or so, but the
pilot lamp blinked and the cooling fan moved. I remembered a similar
problem with broadcast waveform monitors and vector scopes, and replaced
all of the smaller low voltage electrolytic condensers in the circuit
that drives the inverter. Now, the same delay but the fan started and
the pilot lamp lit. There were some bright green blobs on the screen,
adjustement of the focus control produced brilliant menu text. After
exploring the controls, I found that one of them had to be pushed in to
display waveforms. I spent an hour or so exploring the locking action of
the pushbuttons, and there was no was to get two of the switches to
latch in, even if I borrowed the latch pins from other switches. The
others that were supposed to latch did. Because the buttons are plastic
stems on the switches, I filed a notch in the bottoms of the two that
would not latch. This allowed them to latch in, a gentle lift released
them. Everything seemed to work fine, the scope has many features I will
probably never use, but it displayed waveforms and would store them.
After several hours of cooking, I put the shield cover over the power
supply section and the brace that supports the top circuit board back
in. I turned it on, and was met with a total disaster. The only thing I
could get on the screen was blobs bouncing around. I shut it off
instantly, and started looking for bad solder joint on the bottom board
where the power supply is located. A solder splat was found and removed,
the scope came on and performed fine. After a few more hours of cooking,
I put the case and back panel on and ran it on test for a few more
hours. It performs very well, it will probably be used mostly in my
shack to troubleshoot RF circuits and monitor transmitter outputs
because it has a 100 MC. vertical bandwidth.

These are examples of the kind of projects I really like. Now, does
anyone have a 224 handheld scope project they would like to find a home
for? 73.

Bruce Gentry, KA2IVY

Hi Tom,

You must have done that calculation before the thread caught my
attention.

I've checked everything I wrote, and I don't see anywhere that I
have said, "but they might still have made a mistake" as you appear
to be attributing to me.

When did I write that, or are you simply making up quotes for effect?

Tektronix had excellent engineers. Way better than most, but in
terms of reliability, they very often compromised the quality of
their designs in production by using poorly specified parts, and
cheese ball fixes for their mistakes. Their "tented" parts are
legion, and some are very embarrassing to see as an engineer.
(See 2465 A1 board for plenty of examples...)

That said, it is a fool who changes the arrangement or parts
selection, of an RF circuit he does not understand.

-Chuck Harris

Tom Lee wrote:

Thanks

larry

I have a pile of old IBM and Telex terminals from a local school system
when the state moved away from old IBM mainframes. They are stored in my
garage, but I am unable to get to them without help. The IBM terminals are
color, but I don't rember the model number. I believe they are RS232. Most
of the Telex were dead, but I had swapped enough bords to get some of them
to wake up. I am in North Central Florida.

On Tue, Nov 24, 2020 at 2:03 PM cheater cheater <cheater00social@...>
wrote:

Thanks everyone. Not really bothered about the dependency on a control
unit for two reasons. First of all, finding /anything/ of this era will be
difficult, whether it's the rarer RS232 kind, or less rare control unit
based type. Second of all, emulating the bus will likely be part of an
interesting challenge and a good way of figuring out the inner workings of
the display and input device, which is what I want to do, so rather than a
problem it's a positive thing for me. A $10 computer nowadays will be able
to do the job. My current biggest problem is locating those older terminals
in the first place. My assumption is they're mostly in defunct computer
graveyards, warehouses, university store rooms, or bank or utilities store
rooms, dusting and decaying away.

Carbon Composition resistors absorb moisture. Bake them for a while before
tossing them out. Also, high value resistors require voltage across them to
work at their marked value This used to be plainly marked on reels of CC
resistors. I posted a scan once. I caught hell for 'making up that
bullshit'. They also don't realize the first resistor series was 50%
tolerance. yet they were working on pre-war radios. Once again I was told
that I was 'making up that shit'.

I have just checked input resistances on a working-to-spec 7A26, the results are quite unexpected!. If I use an analogue meter and have the 7A26 powered off then in the 10mV position the DC 'resistance' from each BNC centre pin to its outer is about 350k measured in both polarities. For 20mV and higher the resistance is 1M. If I use a DMM then with either power on or power off the 'resistance' is 1M as it should be. Clearly Q150 needs to be powered in order to have its gate reverse biassed.

Even if Q150 is faulty, its output, together with the output from the 2X balance pot R160 form the two inputs to the differential amplifier U1350, so if U1350 onwards is all OK, the trace should move.

I have just noticed that there is another DC balance pot (R1353) between U1350 and U1450 so that can also be used to narrow down where the fault is. Since the two beams do move in response to the vertical position front panel control it looks like U1550 in each channel is OK so you can swap the good IC from one channel to the suspect position in the other channel and see what changes.

Regards,

Roger

On Thu, Nov 26, 2020 at 03:01 PM, Jeff Dutky wrote:

....
My only other complaints about PayPal are mere hearsay, but I've heard too
many stories of sellers having their funds frozen over the years to think
that maybe there isn't at least a little bit of fire behind that smoke.
....

-- Jeff Dutky

I thought about this a bit, with the huge volume of paypal transactions every day across the world, the actual number of horror stories would have to be a fraction of a fraction of a percent.

I don't recall seeing it in any Service Manual, but our good friend H?kan has produced a document on the topic:



Colin.

Once I had the same issue with the 492 attenuator. Taking it carefully apart, one of the wafers was burned. I was able to manufacture a wafer myself, using very thin teflon laminate and 0402 SMD resistors. The result was acceptable up to about 8 GHz.

Cheers

Ulf Kylenfall
SM6GXV

OK, yuzz made me look. I found the schematic for the 475A, and my quick assessment is that there's nothing special about low capacitance or inductance or precise value of the R1356/R1544 combo. I also looked at the regular 475 schematic, which appears about the same. Without seeing the actual physical layout, I'd guess that the circuitry is quite crammed in there for space reasons, and two 1/2W resistors "fit" better than a single 1W piece - enough so that it was worth continuing the tradition over modifying the board layout.

Q1344 and Q1352 form a shunt-feedback linear amplifier, and the rest of the circuitry handles all the various conditions the Z-axis must take, which are plentiful. The collector of Q1352 is a low impedance node by virtue of the amplifier power gain, with DC feedback from R1369, while C1352 provides AC feedback and compensation. The output has to drive the DC restorer, a significant capacitive and nonlinear load. R1368 isolates the DC restorer load, and C1352 stabilizes the amplifier - it would likely oscillate otherwise. The presence of all the diode clamps and blocks in the amplifier stages indicate a number of operational conditions are needed, depending on what's going on in the horizontal system.Q1352 provides strong pull in the down direction, while Q1358 and Q1354 form a cascode amp for the up direction, but only during transient conditions - at DC, it's a constant current source. It looks like the two Rs in question supply collector load current for Q1352 whenever Q1358 is in cutoff, to keep the loop closed and ready for fast response to the next event, or from overdrive recovery. Z-axis amplifiers don't need high fidelity, but do need fast response in one direction at least, to properly unblank at the beginning of the trace. The tail end (blank) can be slower since the trace is usually off screen by then.

So anyway, I wouldn't worry too much about these resistors. Yes, there must be a reason they went this way, but whatever it is, I don't think there's anything critical about these parts. The maximum DC in them should be about 7 mA, so about 700 mW, when the output is held near zero. Two 1/2W resistors standing upright should handle it OK - better than a single 1W part laying on the board.

Happy Thanksgiving all. Enjoy.

Ed

Colin and Juoko,

If the 7A26 is arranged anything like the 475 then cleaning the AC/GND/DC coupling switches is almost exactly the same as cleaning the rest of the attenuator switches: soak a narrow strip of 100% cotton bond paper in IPA, slide it between the open switch leaves and the contact plate on the PCB, close the switch trapping the strip of paper, gently pull the paper out, and repeat several times for each contact point. I found the process more difficult for the attenuator switches on the 475 because you have to remove each attenuator block to get access to the switch contacts, and because there are contacts on both sides of the PCB, the ones on the bottom side being significantly more difficult to access. That said, with patience and diligence I was able to clean all the switch contacts, so I think you shouldn't have any trouble.

-- Jeff Dutky