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Both the voltmeter and the 2430A. There's not much garbage on it but I did hang another cap on it and it made no difference.

Here is a shot of both sides of R873 on the 2430A. At power off, both traces are together. The top one is the at the junction of R873, R876, Q879 E. The lower one is on the C494 side. This was caught just when the sweep was turned to 100ns/div. I quickly hit Save when it happened.



Thanks!
Vince.

--
K8ZW

David,

Hopefully there is an active HP group where you can get more informed assistance on your 1740A.

I will say this: Many years ago,? I purchased a used HP all vacuum tube oscilloscope, which was initially a fine instrument. However, after a week or two, it stopped working. I opened it up and discovered that the deflection amplifier output tubes, which ran quite hot, were in sockets which were attached directly, and only, to a large printed circuit board. Those tubes were literally falling through holes in the PCB which were the result of the heat from the tubes dessicating all of the resin from the board over how many years old (Probably 10 to 12) it was.

Fortunately for me, I had purchased the it from a reputable dealer who, upon return of the HP o'scope, allowed me to apply 100% of its purchase price towards a used Tektronix 561A, along with a variety of plugins. I still have the 561A. It now lives in my closet, along with the plugins, having been supplanted by 46x, 5000 and 7000 series instruments. It still works and I had to dig it out last year to use as my 5000 required repair. The 561A did yeoman work once again, helping me to repair its somewhat newer brethren.

I guess the moral of this story is that HP was capable of, and did, build some excellently performing oscilloscopes, but their idea of quality construction wasn't even in the same league as Tektronix. This is why you see very few classic HP scopes. Worldwide, aerospace and military buyers prized the reliability and longevity of Tek o'scopes so, over the years, they purchased them by the hundreds of thousands. Also, because Tek o'scopes were so long lived, many survived long enough to be retired due to obsolescence, not failure, and surplussed out.

Regarding the 1740A: Just as the much older model of my experience, it is not exceptionally solidly built. Beware the Schadow push button switches. They are commercial grade parts and notorious for having corrosion build up on the contacts. They can be serviced but its not a congenial process, requiring the use of some somewhat nasty solvent based chemicals and a tiny bit of VERY fine abrasive powder which must be completely removed once its done its work.

Thomas Garson

Aural Technology, Ashland, OR

-------------------------------------------------------------------

Lots of vintage stuff pricing is quite high these days. I also collect 8 bit computer junk and for example a digital doorstop like a Commodore 16 is priced in the 400-500$ US range these days.

On the Tektronix side I've noticed far fewer letter series plugins these days. Sampling and spectrum analyzers are rarely seen now IME.

I guess all the ones worth snapping up have been snapped up, certainly by one person (who could it be) who has a closet full of them and never uses them...

On Tue, Sep 1, 2020 at 8:15 PM Vince Vielhaber <vev@...> wrote:

Ok, Q879 collector is solid. When things go sour, it stays. The base
voltage is moving, as is the emitter. So it's being told to compensate
for the change. However, under normal conditions, the collector voltage
is lower by a few hundred mv than the schematic calls for while the base
and emitter are within a few mv.

How are you measuring the collector voltage?
The switching frequency is ~25kHz, and it's going to be ugly as heck if the
capacitor is out, so the instrument you're using to measure this and its
bandwidth are quite important. The average or RMS voltage there just isn't
super important :).
What happens if you tack on extra capacitance from Q879 collector to
ground? You probably want a capacitor that's fairly low ESR, the ripple
current is going to be something wicked if the average current is 3A (see
below).

Under normal conditions there's a
300mv drop across the shunt.

That looks sane according to the voltages annotated on the schematic.
That's a 3A nominal load, though.
U870A/B are the current/voltage controls, respectively, or-ed together
through the diodes. You can tell which one is in control by the voltage out
of pin 1/7.

Going to take a closer look at Q879's feed.

Have fun!

Assuming a VBE drop across the sensing resistor, then you're drawing roughly half an amp.

Harvey

Ok, Q879 collector is solid. When things go sour, it stays. The base voltage is moving, as is the emitter. So it's being told to compensate for the change. However, under normal conditions, the collector voltage is lower by a few hundred mv than the schematic calls for while the base and emitter are within a few mv. Under normal conditions there's a 300mv drop across the shunt.

Going to take a closer look at Q879's feed.

Vince.

--
K8ZW

My mistake: HP1740A.
I get the impression vintage TEK scopes are ten times the price they were ten years ago, and now rare. My HP1740A was from a recycling centre for next to nothing, just needed switch cleaner.
And thanks for the recent information: very useful.
Regards
David Collier

Hi Nick,
It doesn't help you any further, but in a rather tricky way I managed to create a horizontal gap in AVG waveform acquisition. And indeed a (dotted) linear interpolation line between the dots at the ends of the gap was shown. Since the vertical digitizing in your video seemed to miss or add a sign bit during part of the trace it seems that both vertical and horizontal digitizing suffer from DAC errors.
Albert

Raymond: I only need 1 Lemo 4-pin plug. How much would it cost me to have
you send me one? How would I pay for it? Here is my address:

Gary Bosworth
139 E. Shrode Street
Monrovia, CA 91016

Cellphone: 626-803-8336
e-mail: grbosworth@...


On Mon, Aug 31, 2020 at 10:09 AM Raymond Domp Frank <hewpatek@...>
wrote:

On Mon, Aug 31, 2020 at 06:04 PM, Gary Robert Bosworth wrote:

If the
connector is the correct one (it is only about 5/16" diameter with a
"D"-shaped 4-pin insulator inside), name your price and I will pay

through

any means you desire. I will contact you in a day or so to remind you of
my needs. Bye for now.

Hi Gary,
I checked. It is indeed the connector that I thought. It is the same Tek
used for the power supply connection of probes like the P6201 and P6202A.
You'll find the same sockets on 'scopes like the 7104, 7854, 7904(A). It is
Tek part no. 131-0778-00. The 1101 PSU has four sockets for them.

I checked and double-checked the Lemo part no: FFA.0S.304.CLAC42. Digikey
(USA) currently has 5 in stock @ a lot of money, something like USD 30.

I have only a few left (as sets with sockets, actually, have a few more
sockets and counter-plugs) and sending from the Netherlands may be costly,
maybe about (half) as much as the Digikey price. That would leave little
left for me if I'd want to "compete".

Have a look and if you still want me to send one (Digikey total cost,
order cost), let me know your ZIP code, I'll check postal costs and we can
go from there.

Raymond

--
Gary Robert Bosworth
grbosworth@...
Tel: 310-317-2247

I was given an old 547 that was set for scrapping. It that had some high
voltage issue. The tubes were partially pulled but it seems intact
otherwise.

I'm located in Austin Tx if anyone wants to come pick it up.

I did a search and somehow this one slipped through the net:



FG502 Teardown and Repair by Paul Rako, mis-titled “...FG503....”

Shaun M.

<>

Look up " james_s <>" on
EEVBLOG. He has a much better solution. i would show you a picture, but I
don't know how in here.

On Sun, Aug 30, 2020 at 12:23 PM maddisassembler <
320041677522-0001@...> wrote:

Hello all,

a TDS3054 (built in year 2001) shows the following symptoms when connected
to power:
- 'A system error has occured', Error Count =11, 'display error', goes
away after short power off/on
- Unrealistic high 'total operation time' (16350105 hours)
- Impossible time setting (e.g. '11:80:21')

Topic #157465 also deals with this issue, the problem is data corruption
inside
U640 DALLAS DS1742W, exhausted lithium battery, date code on the
package is '0029'.

I ordered replacement DS1742W via Amazon in China (the chips I received
seem fully functional when
tested on a programmer), date code on the package is '0945'.

How should I prepare the new DS1742W I am going to install in the scope?

Simply read out the (most probably) rubbish of the old DS1742W and copy
it to the new one?

Is a memory map available somewhere which shows the addresses of the
relevant memory locations and their expected content in a working scope?
(the address locations 0x7F8...0x7FF are described in the DS1742W data
sheet)

I cannot believe that appr. 2k of memory are fully used to store internal
scope
status data.

Thanks for any help!

Best regards
-Roland

On Tue, Sep 1, 2020 at 03:39 PM, teamlarryohio wrote:

BTW, they're right below the RPR directory

Don't know where "right below.." is.
I've taken the liberty to introduce the term "Replaceable Parts Registry" on Tekwiki for those who don't know the term "RPR" (yet).
Both terms give ahit now.

Raymond

On Tue, Sep 1, 2020 at 10:04 AM Siggi via groups.io <siggi=
[email protected]> wrote:

On Mon, Aug 31, 2020 at 8:36 PM Vince Vielhaber <vev@...> wrote:

The 5V jumping around is the 5V regulated that C494 is on. There it
drops a volt or so when I switch below 200ns. According to my Fluke,
when it goes out completely it holds at 3.93v.

Oh, interesting. I assumed you were talking about the 5VD, which is the
main switch-mode regulated supply that feeds all the digital logic.

You're talking about the linear regulated 5V supply. Same deal though, go
back to the first decoupling cap, see whether the supply is jaggy and
whether the raw supply holds up when the regulated supply drops. Most
likely - as others have noted - this is due to geriatric bulk caps in the
secondary, so check that first.
If the raw supply is holding up OK when the regulated supply drops, then
you move downstream and see what's up. This supply is current limited, so
you can infer the current it's using by measuring across the shunt.

Incidentally I'm not finding a power distribution diagram in the service
manual. Looking at schematic <10>, though, you'll see that the peak
detectors and the CCD arrays run on the +-5V linear regulated supplies, so
that'd explain why one or both of those is getting dragged low when the
sampling speed is jacked up.

On Mon, Aug 31, 2020 at 8:36 PM Vince Vielhaber <vev@...> wrote:

The 5V jumping around is the 5V regulated that C494 is on. There it
drops a volt or so when I switch below 200ns. According to my Fluke,
when it goes out completely it holds at 3.93v.

Oh, interesting. I assumed you were talking about the 5VD, which is the
main switch-mode regulated supply that feeds all the digital logic.

You're talking about the linear regulated 5V supply. Same deal though, go
back to the first decoupling cap, see whether the supply is jaggy and
whether the raw supply holds up when the regulated supply drops. Most
likely - as others have noted - this is due to geriatric bulk caps in the
secondary, so check that first.
If the raw supply is holding up OK when the regulated supply drops, then
you move downstream and see what's up. This supply is current limited, so
you can infer the current it's using by measuring across the shunt.

Per Dave Brown:

That's the purpose of the common parts catalogs of which we also got >a

release and are posted on TekWiki. I don't know if they all are there >but
they can be scanned and uploaded.

They've served me well for around 40 years. There are more of them up on
the wiki than we had in the service center.

BTW, they're right below the RPR directory.

-ls-

I wouldn't even think of interfacing the 1S1 with anything other than a 530,540.550 series Tek scope. It's a complex interface, involving not just the connector but several different power supplies ranging from 6.3 volts up to 500 volts. The plugin also has to sink 150 mA at 75 volts from the mainframe. The differential output of the plugin has a 67 volt common mode component that matches the input requirement of the 500 series Tek vertical amplifiers. Some of the 540/550 series also had a sync interface. The only thing you can do is keep your eyes peeled for a suitable mainframe. The most desirable one IMHO is the 547 although it is prone to the HV transformer thermal runaway problem. The 535A which does not have that problem would be the next best.

Good Luck!

Morris

Still refuses to do any AQS's at all.

You probably tried AQS because I pointed to that. Something very strange is going on with AQS in my 7854 (or with my brains?) AQS worked at 0.5 ms/div but not at 0.2 ms/div and faster. OK. Later on I thought to remember a trick to mislead the scope: set trigger level for not triggering, then do AQS (the scope waits...), then switch to faster sweep rate, then turn trigger level produce a sweep. Somehow it didn't work, error all the time. I switched off the scope and read the operators guide. AQS: works ONLY with 7B87! But I used a 7B80 (no 7B87 at all in the scope). And AQS just worked fine at 0.5 ms/div.
Back to the 7854 to do it once more. And this time AQS gave an error beep all the time!??
I have a 7B87 but didn't succeed to AQS a waveform with gaps. The manual says that "empty" horizontal locations are filled with the last valid data at the left side, so not by interpolation between two valid data points.

I did notice though
that during an AVG acquisition (when the issue was active) if I already have
it in digital mode. I could actually see it missing chunks as it gets data and
then just filling it in with weird stuff at the end, making those slopes and
spikes (badly trying to interpolate the missing sections of the wave?) *see
first video for alright example.
[this one: Broken video: ]

Very nice video. Indeed seems to show interpolation afterwards.

.... when I tapped on the transistors in the
horizontal section, suddenly it worked just fine!

You might "jiggle" circuit boards and connectors as well, who knows...

No pictures this time but, (YET AGAIN) it's changed behavior, now its getting AVG acquisitions (mostly) fine (As in not erroring out but still occasionally having some weird defects to the wave but now everything is the right size and, mostly intact). Still refuses to do any AQS's at all. I did notice though that during an AVG acquisition (when the issue was active) if I already have it in digital mode. I could actually see it missing chunks as it gets data and then just filling it in with weird stuff at the end, making those slopes and spikes (badly trying to interpolate the missing sections of the wave?) *see first video for alright example.


Never mind, in the middle of writing this I turned on the scope to check ( sat for a few hours powered off ) and it was doing it again, but I've discovered something very strange that may have solved (at least a small part of and temporarily) the mystery of this thing when I tapped on the transistors in the horizontal section, suddenly it worked just fine! This thing is weird, doesn't make much sense to me as they aren't even the metal potted ones but the ones in the heat sink clamps. Luckily I took some video this time, first before the miraculous (and likely temporary) fix and again when it started making proper acquisitions. Still won't do AQS under any settings though.

Broken video:
Working video: (flashing on analog side is from a dirty pot I'm fairly sure)

Also Dave, you are definitely right about which transistor that is, thank you for finding it for me. According to my service manual A17Q141 to be exact . Although Q141 (and it's paired Q41) are PNPs ( tek part no.151-0220-00 ) but I can't really find any other specs than some incomplete ones I scraped together, having some difficulty locating an equivalent replacement if case I need it, but I may just be bad at looking (don't know if you can fudge the numbers a bit like some caps)

Tomorrow, if I have time after work, I'll finally check the power supply and see if it's correct or not. Sorry if this was a little rambly, I should have called it a night hours ago.