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My "new to me" TWD120 arrived today. Thank you Charlie.

As Charlie advised in previous email, it did not pass self test, leaving the front panel LED unmistakably solid red.

However, the repurposed IBM laptop external power supply worked admirably so I dove into it.

After removing a number of screws and a cal sticker, I was presented with a single nice and compact SMD loaded PCB. No out-sourced PWM supplies for Tek. The regulator circuitry occupies a compact "can" in one corner.

As I was working w/o a schematic I had to find supply lines on some chips to check voltages. Voltages were good, but one was a bit noisy. DC to DC portion of supply looked good on (Tek 5000) scope. After sniffing around a bit (figure of speech. It did not smell) I noticed several Motorola T10N05e TO-263 type SMD packages near the supply wall, but outside of it. At first I was puzzled as I could find these parts for sale but no data sheet. Figured out they were N-channel power mosfet. I determined they were used for gates to enable/disable DC power feeding from the supply. Interesting. Squinting trough my trusty Swiss Army Knife magnifier (glass lens!) I noticed serious corrosion on the Source solder connection of one of those FETS (Q104: +8v line), which I theorized may have been the source of the noise I has seen. Reflowed the funky joint. Kicked on the power, waited a minute or so for self test to complete: Bingo! LED now turns Green!

That's as far as I got today. Next thing is I have to pull the software for it off of the floppy discs (fingers crossed) for copying over to the server and then burn a back up disk. After that, get my Win98SE PC set up with SCSI (not too big a deal as I used to do a lot of SCSI stuff) and see if I can actually get the thing to work. At the moment, I'm fairly optimistic this will happen in short order.

A few photos here:


Thomas Garson
Aural Technology, Ashland, OR
By my calculation, the dynamic range of the universe is roughly 679dB,
which is approximately 225 bits, collected at a rate 1.714287514x10^23 sps.

guess lockdown has made some people a bit silly.

If you are in the environs of Calgary, or just plain rich, and intent on getting a 535.... there's one for sale there, for just 3,000 CDN.
And the ad says, it comes with a cart that tilts too!
What a deal, eh.

I am looking for a front "clip-on" cover for a Tek2225 but they seem as rare as hens teeth - but it occurred to me that a cover from another scope in the 22xx range may fit.

Can anyone suggest a likely range ??

Before some kind soul offers me one it would need to be in the UK or Europe otherwise the shipping costs become prohibitive :-(

Best regards,
Dave

I have had some further observations, not good, I'm afraid.

I thought that I would leave the scope in "store" mode and see if any improvement happened. It didn't. When I powered down, left it a while and then powered up in "non-store" mode, I was hoping to see the scope working as it had been before, but the screen was totally blank; no beam, no beam-finder, no readout. I have checked all of the low-power voltages and they are all within spec. Also, I can see the saw-tooth output on the back of the scope, so some circuits are working. However, the -1475 V high voltage is absent. I assume this will have the effect of losing the beam, but what could have caused it's failure?

Another anomaly is that the voltage at the "collector" test-point on the storage board is -1.4 V, when it should be +150 V.

I would certainly like to get the "non-store" mode working again, possibly by repairing the -1475 V on the CRT, then assessing why the storage mode wasn't working properly.

TIA, Colin.

Hi Gary,

The very first thing you need to do is to measure the low voltage test
points for DC level and ripple. They are marked on the board. These
scopes usually have bad electrolytic capacitors and you need to test for
that.

The service manual will tell you what to measure and what to expect.

The correct manual can be had here.



Regards,

Tom

On 9/20/2020 7:41 PM, gary@... wrote:

I have a 465B/DM44 that is new to me that I think has issues. I am a relative newby to scopes, but this one does not seem right. There is "compression" of the horizontal trace, but it varies. Sometimes the trace just shrinks to a width of about 1-1.2 major graticule (1/2" in the same spot), other times it only shrinks a bit, covering about 7.3 graticules, with the best it ever gets being about 9.6 (full screen = 10). This significant compression happens randomly, both when scope is relatively "cold' and after it is fully warmed up. It affects both channels. I've used different probes - no difference. I can impact this, by moving the sweep left to right with the horizontal position control. This sometimes moving the horiz position "fixes" it, other times not. If it is temporarily working OK, I can get it to shrink if I aggressively manipulate the horiz position knob. In addition the "timing" may not be correct - not sure I am saying this correctly, but the calibration square wave gets "smaller" horizontally as the trace moves from left to right. I would expect the length of the square wave to be the same all across the screen. I suspect this is related to the compression, but not sure - seems relevant to mention. The only thing I have done is removed the cover and made sure the connections to the deflection plates on the CRT were secure (they appeared to be). Everything looks clean and untouched inside, and overall the unit is clean and does not look abused. I have not cleaned any switches or controls, but that seems like a good place to start. If it matters, serial number is above 60xxx, which I believe makes it the later series. I have downloaded the manual from the TEK site, but they only have the low S/N version. If it would help I have photos and even short video of the bad behavior.
I come here seeking help, on how to proceed, possible causes, how to troubleshoot. Thanks in advance Gary.

--
This email has been checked for viruses by Avast antivirus software.

Note: this post was initially posted to Tekscopes2. That post has been deleted.

Thanks Shailendra, Cleaning the pots will be the first thing i do when i open it up again. My go-to is Deoxit-5.

Hi,

How on earth did they lose the package?

Szabolcs


Martin Whybrow <martin@...> ezt írta (id?pont: 2020. szept.
22., K, 10:49):

I have faced a similar problem on my 465B. In my case, horizontal sweep used to shrink and expand at random. There was no linearity issue, as calibrator square wave looked uniform across the width of display, only shrunk randomly to anywhere from six to ten horizontal divisions. Fault was traced to an intermittent x1 gain setting potentiometer in the horizontal amplifier. This pot was replaced and gain adjusted as per service procedure, and scope has worked fine since then.

In your case, it may be a noisy horizontal position potentiometer, in addition to x1 gain potentiometer. Since you have linearity problems also, as you see shrinking of square waves at some positions of screen, there could be linearity problems in sweep area, or some limiting due to a failing component in one half of the horizontal amplifier section.

My two cents to share, hoping you can get some ideas to explore.

Shailendra

A fairly robust way of buffering would use a fast PNP transistor and a fast NPN transistor with the bases connected together and the emitters connected together; PNP collector goes to the Vcc supply; NPN collector goes to ground. Input to the (connected) bases and output taken from the (connected) emitters.
Shoot-through is impossible and current drive (both positive and negative) can be quite large. Voltage gain is unity, reduced by the EB drops. Efficiency is quite high. As long as you don't need voltage gain, this should work quite well. BTW, this also works very well for driving power mosfets.

SCM

On Sun, Sep 20, 2020 at 08:03 PM, Raymond Domp Frank wrote:

A simple pin-converter is needed: A 24-pin socket for the DS1742W is placed
above a 32-pin socket + header with pins 7 - 28 of the DS1250W corresponding
with pins 1 - 24 of the DS1742W.
Pin 29 of the DS1250W is re-routed to pin 21 of the DS1742W and pin 32 of the
DS1250W is re- routed to pin 24 of the DS1742W. The original straight-through
connections of these two sets are removed, the remaining 22 connections go
straight-through.
I haven't yet looked at possible WE/OE/CE (timing) discrepancies in the
programmer but I'm confident things will be OK. Only the first 2K of the
"DS1250W" will be written.

I'll report back (or possibly, continue this monologue) with results.

In my ecstasy about the successful revival of my TDS3014B's Ethernet interface using the procedure described above, I forgot to thank those who helped me.

Thanks!

Raymond

Hi Gary:
See,

to download Tektronix's superb and easy to follow (compared to the stuff we get today.)
There is a lot of info on the Web about this very popular scope... just Google.
I suggest, read the 465B user manual to make sure you understand what the unit can, is supposed, to do. (Based on that understanding, you might have a better understanding of what issues (if any) the unit has.
A search on messages in this forum will also yield plenty of info/tips on these scopes.
Yes, post a link to your photos/video on Google Photos, Imgur... and video to YouTube... and people on the forum will take a look.
There are many very knowledgeable people on this forum, who generously share their time. Let us make best use of that.
Regards.
Roy

John,

A bipolar or JFET buffer is quite feasible but the collector (drain) load resistor has to be quite a small value. With the semiconductor turned off the resistor has to charge up 4 gate input capacitance plus stray capacitance in around 5nsec ( 1/4 period at 50MHz), 20pF total capacitance requires around 220R load resistance.

Roger

Its probably a bit academic since I have ordered replacement parts, but funnily enough I was just wondering whether a transistor (or JFET) could be used to buffer the output and reduce stress on the crystal. Just needs one that can comfortably handle the switching speed I guess. Perhaps worth a quick test....

If you don't want to wait that long, you can temporarily add a NPN switching transistor as a simple pulse inverter.

Input via 1k to the base, 10k between base and emitter, emitter to ground.
Pull up resistor of 1k from +5V to collector, collector as output to the 112's

This way you ignore the lower output level of the oscillator.

Quick and dirty, I agree...

Leo

satbeginner, that is a good point, thank you, but yes, just to confirm 5V and GND were present at the oscillator and the 74S112 chips when I ran the tests.

Just another update on the crystal saga (the last one for now!), I ran the crystal test for about 10 mins yesterday but decided to do a further soak test this morning. Must have ran it for about an hour. Results initially were the same as yesterday: The top peak hit about 4.2V without load, about 3.5V when loaded down with a 470Ω resistor. However after an hour, the top peak was at just +2.6V. Not sure exactly how long it took to drop to that level, but wouldn't that be rather borderline for TTL?

In any case, replacement crystal ordered so will be able to compare when it arrives.

I have a 465B/DM44 that is new to me that I think has issues. I am a relative newby to scopes, but this one does not seem right. There is "compression" of the horizontal trace, but it varies. Sometimes the trace just shrinks to a width of about 1-1.2 major graticule (1/2" in the same spot), other times it only shrinks a bit, covering about 7.3 graticules, with the best it ever gets being about 9.6 (full screen = 10). This significant compression happens randomly, both when scope is relatively "cold' and after it is fully warmed up. It affects both channels. I've used different probes - no difference. I can impact this, by moving the sweep left to right with the horizontal position control. This sometimes moving the horiz position "fixes" it, other times not. If it is temporarily working OK, I can get it to shrink if I aggressively manipulate the horiz position knob. In addition the "timing" may not be correct - not sure I am saying this correctly, but the calibration square wave gets "smaller" horizontally as the trace moves from left to right. I would expect the length of the square wave to be the same all across the screen. I suspect this is related to the compression, but not sure - seems relevant to mention. The only thing I have done is removed the cover and made sure the connections to the deflection plates on the CRT were secure (they appeared to be). Everything looks clean and untouched inside, and overall the unit is clean and does not look abused. I have not cleaned any switches or controls, but that seems like a good place to start. If it matters, serial number is above 60xxx, which I believe makes it the later series. I have downloaded the manual from the TEK site, but they only have the low S/N version. If it would help I have photos and even short video of the bad behavior.
I come here seeking help, on how to proceed, possible causes, how to troubleshoot. Thanks in advance Gary.

I'm after the external keyboard for my 7854; I found one at a good price on ebay and bought it, but ebay's GSP managed to lose the package. All the other units are either stupidly priced or the seller wants more for shipping than the item itself is priced at. I have only found these in the US, and shipping to the UK is prohibitively expensive in most cases. Does anyone have one they want to part with, preferably in Europe or willing to ship for a realistic cost from outside of Europe?

"I hooked it back up to the board using jump leads, powered up the 5V rail but there was no output. I hooked up the sig gen again and got output from both 74S112s. "

Do you have the onboard 5V checked at the oscillator as well??
And the ground to the oscillator?

5V onboard does not mean it is 5V everywhere.

Just my 2cts

Leo