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Re: 1S1 sampling unit; (also 7B53AN & 7A18 plugins)
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... |
Re: Strange Tek2440 issue
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 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 aThat 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! |
Re: Strange Tek2440 issue
Assuming a VBE drop across the sensing resistor, then you're drawing roughly half an amp.
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Harvey On 9/1/2020 8:15 PM, Vince Vielhaber 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.? Under normal conditions there's a 300mv drop across the shunt. |
Re: Strange Tek2440 issue
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.
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Going to take a closer look at Q879's feed. Vince. On 09/01/2020 10:03 AM, Siggi 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 itOh, interesting. I assumed you were talking about the 5VD, which is the --
K8ZW |
Re: 1S1 sampling unit; (also 7B53AN & 7A18 plugins)
David Collier
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 |
Re: Tek 7854 intermittent issues
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 |
Re: 4-pin Lemo connector used on end of cable for 4041 PD keyboard
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:--through Gary Robert Bosworth grbosworth@... Tel: 310-317-2247 |
Re: TDS3054 Replacement of DALLAS DS1742W (U640), data content in NV-RAM
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, |
Re: Reverse part lockups
On Tue, Sep 1, 2020 at 03:39 PM, teamlarryohio wrote:
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 |
Re: Strange Tek2440 issue
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:Incidentally I'm not finding a power distribution diagram in the serviceThe 5V jumping around is the 5V regulated that C494 is on. There itOh, interesting. I assumed you were talking about the 5VD, which is the 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. |
Re: Strange Tek2440 issue
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 itOh, 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. |
Re: Reverse part lockups
Per Dave Brown:
That's the purpose of the common parts catalogs of which we also got >arelease 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- |
Re: 1S1 sampling unit; (also 7B53AN & 7A18 plugins)
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 |
Re: Tek 7854 intermittent issues
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 thoughVery nice video. Indeed seems to show interpolation afterwards. .... when I tapped on the transistors in theYou might "jiggle" circuit boards and connectors as well, who knows... |
Re: Tek 7854 intermittent issues
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. |
Re: Strange Tek2440 issue
Hi,
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I would first check the power supply. I'm not a big fan of "the universal internet method of fixing everything", that is indiscriminately recapping stuff, but in the case of the 24xx family DSOs, I had 3 of those and all had practically every cap failed in the PSU. So a complete replacement of capacitors at the secondary side is one thing I would do first at the slightest suspicion of power problems. Szabolcs Vince Vielhaber <vev@...> ezt ¨ªrta (id?pont: 2020. aug. 31., H, 20:04): Acquisition stopped, doesn't happen. I can go all the way to 2ns/div. |
Re: Reverse part lockups
That's true when looking for Tek part numbers. The added value of OCR here would be *reverse* use: "What's the Tek no. of a 2N4275?"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. Dave |
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