Date   

Photo Tek2465 error display.jpg uploaded #photo-notice

TekScopes@groups.io Notification <noreply@...>
 

The following photos have been uploaded to the A5 repair attempt album of the TekScopes@groups.io group.

By: Rogerio O


Re: OT - RIFA caps & 'transformerless' PSU

Brian Cockburn
 


Re: Another A5 board repair attemp - help needed

satbeginner
 

Btw, here's the link to your album:

https://groups.io/g/TekScopes/album?id=256231

Saludos, Leo


Re: Another A5 board repair attemp - help needed

satbeginner
 

Clean the Beamfind switch first, then try again.

Leo


Re: Clean and Lubricate Pots in Tek 475

Ed Breya
 

First try lubing the pot shaft bushings from outside - remove the knobs, and give them a generous drenching with light oil, then rotate them lots of times (put the knobs back on if necessary). This should loosen them up. Also push and pull on the shafts (they will only move maybe a few .001 inches axially) to help get some oil in, and loosen the crust and gum. If the pots then turn freely, rotate them a bunch of more times to clean up the elements. If after all this, the pots are still binding or noisy, then you may need to take them apart for internal cleaning. If you don't get immediate improvement, let them sit overnight and try again before taking more drastic measures.

Ed


Re: Clean and Lubricate Pots in Tek 475

Simon
 

Some have had success dribbling IPA on the pot shafts with a hypodermic syringe and turning the shaft from stop to stop many times. It helps if the scope is positioned vertically to benefit from gravity.
For calibration you can look through the steps in the service manual, and work out how long that would take with the specified test instruments, then factor in a technician’s labor. It would probably work out more than the scope is worth. They can be picked up for about $250 on eBay and maybe twice that for a fully refurbished one. You can adjust the timebase fairly easily with a crystal controlled function generator, but the vertical amplifier calibration requires more sophisticated instrumentation. My function generator has a TTL output and I swapped the 74LSXX output IC for a 74HCXX and could measure a 5 ns rise time on 10 ns/div so I was happy with the frequency response, but I never got both Y amps the same. To calibrate them, page 75 of the service manual gives you the list of instruments required. It is rather daunting.
It seems a nice idea to restore it to its original factory state, but unless you plan to use it in your job it is probably not worth it.
Simon


Clean and Lubricate Pots in Tek 475

 

The vertical position pots and the beam intensity pot on my Tek 475 oscilloscope are stiff and scratchy. The service manual says that they are pre-lubricated and sealed, and that no regular lubrication or cleaning is necessary, but I think that this may not still be true 50 years after the unit was manufactured.

I can see that the pots have four screws on the opposite end from the control shaft, but I'm not sure what I would have to do to clean and lubricate the pots once I had them open. Also, the pots in question (part #s 311-1397-00 and 311-1533-00 seem to actually be two pots connected to together, in the case of the first pot, which is used for the vertical input position adjustment, they are two 5K Ohm pots, and the second pot, which is the bean intensity adjustment is one 5K Ohm and one 2.5MegOhm pot).

I've already searched for replacement parts, and have found some promising leads, but I would rather clean and lube the pots in-place than have to unsolder anything (which would require significantly disassembling the scope in order to get at the backside of the circuit boards).

Does anybody have experience re-lubricating these pots, and could tell me what I'm up against?


Re: Troubleshooting an old Tek 475

 

Ed Breya wrote:
I don't know about the 475 front ends, but in the 7K ones they use what sounds like the same kind of
contacts, operated by the cam. If the 475 is the same, then there are likely contacts on both sides of
the attenuator board. The ones between the attenuator tubs are usually the easy ones, for access -
they select the tub through-connections. The ones on the other side of the board are the bypass
contacts that pass the signal straight through if all are closed.
There are indeed contacts on the underside of the vertical attenuator boards, but it looks like you actually have to unsolder both the BNC connectors and the connection to the main vertical amplifier board in order to remove the attenuator boards, so I'm not going to do that. Instead I was able to slip a narrow strip of bond paper in through the side and clean most of the contacts that way. There were a couple that I just couldn't get to because they were blocked by the socket housings for the attenuator blocks, but I got to more than half of them, and that seems to be have been good enough. The dirty contact problems on channel #2 seem to be gone, so I'll take that as a win.

I probably need to adjust the horizontal timebase, since I replaced a capacitor on the sweep generator board, and because I have suspected that the timebase may have drifted all along (of course, maybe that was due to the bad capacitor, so that might have been fixed), but I don't have any of the equipment needed to do a real calibration, and the timebase isn't off by enough to make gross adjustments worthwhile.

I also wanted to trim up the probe calibration signal, because it seems to run just slightly fast (or the timebase is slightly slow), but it looks like there is no way to adjust the calibrator frequency, only the amplitude; the square wave period seems to be set by soldered in component values, so I'll let that be as it is (until and unless it becomes a real problem).

So I guess that this is a success. I have regained full function on the instrument, and comparing its readings to those from my multimeters and from the 2213 at least give me good bounds on how out-of-cal the 475 actually is.

Does anybody know how much it costs to have a scope this old professionally calibrated?


Re: Another A5 board repair attemp - help needed

Siggi
 

On Thu, Nov 5, 2020 at 6:42 PM Rogerio O <rodd414@gmail.com> wrote:

Would a broken A5 board produce a screen like the one I am seeing?
Is your beamfinder switch perhaps stuck? This looks exactly like my 2467
did before I re-animated the beamfinder switch.


Re: TDS510a Power Supply

Siggi
 

On Thu, Nov 5, 2020 at 5:35 PM Derek Chauran <af7ux@outlook.com> wrote:

Thanks, as I mentioned, I am a novice at all of this, so it is very
helpful to have pointers as to what to look into. I have been reading up
based on your comments. Learning is exactly why I am here, and I have
learned a lot.
The good news is that you have a choice of two cutting-edge scopes as
of early 90s. There were good reasons why each was a Tek product at
the time, and which one is better for your needs will totally depend on you
and your needs. If you're not desperate for the cash, I'd suggest you keep
both scopes for a while, on the same bench, and figure out which one you
prefer.

I'm sure there are others here who're better qualified to speak to these
two scopes than I am, but here's my take.

For most of what I can imagine using the scope for, I will be looking at
repetitive signals. E.g. checking power supplies for ripple, or observing
simple, modulated RF signals (I'm a ham, which is where my interest in
electronics stems from). In other words, I am primarily going to be looking
at analog signals.
Neither scope is going to have any trouble with either of the above, but
depending on the frequency of your RF, the TDS510A may have features such
as high-res that will be helpful.


The 640a manual states that it has averaging, but not peak or high
resolution.
Peak detect (or envelope) is handy when you're looking at a "slow" one-time
signal on a scope with record length that's too short to capture all the
details of the signal. I have a 2430, which has only ~1024 sample record
length, and when I'd use it to e.g. look at a switch mode power supply
startup, I'd use envelope or peak detect to get the envelope of the
startup. Best case you'd want infinite record length so you could capture
forever with full detail. Newer scopes approximate that ideal better and
better.
My TDS784D has a max of 8MS record, which is sometimes marginal. The scope
is also slow as molasses when viewing a record that long, which is also
annoying.


I did a quick read on equivalent time sampling - the 640 has a higher
sample rate (2g/sec) and interpolation, so the net effect is that both
scopes claim an "effective" sampling rate of 100gsamples/sec, but the 640
has a better single shot bandwidth, and 2gs/sec on all 4 channels, whereas
the 510a has 500ms/sec on 2 channels or 250ms/sec on 4.
Yeah, the TDS6XX scopes went all out on realtime sample rates at the cost
of whatever else - record length for one. This was done by capturing the
signal into a CCD storage array at a high rate, then digitizing the signal
out of the CCD at a lower rate. I'm not sure they have equivalent time, as
to do this you need some timing hardware to measure the difference from
sample clock to trigger, and I don't remember seeing that (but I'm often
wrong).
There are tradeoffs to the CCD capture, and the TDS6XX series dials all the
knobs to one side. As a case in point, they're practically blind all the
time - meaning that while they capture a single record in realtime, it
takes a fair amount of time to read the capture out of the CCD, store it in
memory and display it.
You might amuse yourself by hooking the same signal source into each scope,
while using the other scope to look at the trigger output on the back. I
think you'll find that under practically all conditions, the TDS6XX scope
will trigger at a lower rate than the TDS510A.

In the later TDSen this "blindness" - even in the TDS5/7XXen - was deemed
important enough that the DPO feature was implemented. This dials all the
knobs in the direction of minimal blindness to allow capturing and
displaying glitches and other anomalies at the highest possible
probability. I find this occasionally convenient, as by turning on DPO and
infinite persistence, I'm reasonably assured that I'll see glitching
"sooner" than by infinite persistence alone.

The 510a definitely wins in sample buffer size - 50k vs 2k. That said, even
Tek suggests that for most signals 2k is plenty.
Mmmm, yeah, I believe the literature of the time would have said that. I
don't think you'd find many people agreeing with that today. Typically I'd
choose record length over realtime bandwidth - except when I need the
realtime bandwidth :).
On my bench I have a 2467, a HP54622D and a TDS784D, which I use in that
order of preference (mind you, I'm but a hobbyist with a bit of a gear
fetish).
The 2467 is an analog scope that's a total joy to use for repetitive
signals. For slow one-time signals, I prefer the HP, and only when I run
out of bandwidth I turn on the TDS784D to suffer the fans and the UI.

Regarding peak, it looks like the 640a has envelope mode which is fine for
repetitive signals, whereas peak is better for single shot? But that also
means that peak is bandwidth limited on the 510a. Curiously I cannot find
the non-interpolated real-time bandwidth of the 510a, the manual just says
that it will decide when it forces interpolation or equivalent time
sampling.

Yeah, the spec sheets will be shy about their Achilles heels.

I would assume that it's something like 125 mhz?
Ehem, MHz (m is milli :). For sure you don't want to go above 250MHz with
500MS/s.

High res - also a clear winner in the 510a.
I have found this useful on occasion, but again this brings down your
realtime sample rate.


Re: Troubleshooting an old Tek 475

 

I checked with the 2213 and there is basically no discernible ripple on any of the labeled test points (<< 0.1V on all but +50V and +110V, < 0.5V on +50V, and < 1.0V on +110V) except for UNREG +50V which has ~2V trianglar ripple at 60Hz.

The unlabeled test points are a little bit more interesting: +14.64V and -3.776V have no discernible ripple, but -2.411V is actually an asymmetrical square wave with a period of 8ms and a negative pulse of 1.8ms, +34.06V has a 0.2V ripple at ~1.2KHz, and +137.9V has an 8V sawtooth ripple at ~120Hz.

My father took meticulous care of his instruments, and this one spent the majority of the past 40 years in a cool (~65°F) dehumidified basement. I did try to "bake" it dry about 15 years ago in an un-air-conditioned room with a dehumidifier, but I doubt that made any appreciable difference. I'm still surprised that it's has as few problems as it evidently has. I had fully expected all of the electrolytic caps to have gone dry, if not (as with the cap on the sweep board) leaked their guts out.


Added album A5 repair attempt #photo-notice

TekScopes@groups.io Notification <noreply@...>
 

Rogerio O added the album A5 repair attempt: This album contains one photo of the A5 board I am trying to repair and the image on the scree that I get


Another A5 board repair attemp - help needed

Rogerio O
 

Dear all,
I bought a Tek 2465BCT at Ebay.
The scope was damaged during shipping and two control knobs had their shafts broken.
While opening the unit to replace the pots, I used the opportunity to take a look at the A5 board, and as usual, the SMD electrolytic caps had leaked.
Fortunately the corrosion seemed light no damage to the traces and just one pad lost.
I unsoldered the components around the DAC and the 74HCxxx IC's washed the board with water let it dry and soldered the components back.
I had to replace some smd caps and resistors, as well as two 74HC IC's.
I checked the traces for continuity and found no open traces so I was very confident the repair attempt would be successful.
I turned the scope on, heard the "clicks" and the leds flickered as usual but to my surprise, there was jus a "square" four div wide.
The intensity, position and readout controls do not work, but the horizontal seems to work.
So I do not know if there if the problem is on the A5 board or the infamous U800 has also failed.
I have uploaded the photo of the board and the screen I see after the boot in the album A5-repair attempt.
Would a broken A5 board produce a screen like the one I am seeing?

Thank you for any ideas.
Roger


Re: Troubleshooting an old Tek 475

 

John wrote:
It is quick and easy easy to check the power supply outputs with a DMM. In approximately the centre
of the main board, in between the bridge rectifiers and the cluster of 4 large metal can transistors, there
is a group of test points with the voltages marked on the PCB. Page 171 of the pdf shows the board
layout and page 172 the circuit diagram.
Yes, I saw those on my first pass. They are quite well marked with what voltages should be present. There are also five unmarked test points, one next to the INVERT switch, and the other four behind the A TRIG HOLDOFF pot.

I measured all the test points against the test points marked GND (which I had previously tested for continuity). The only standout was the UREG +50V point which read +68.5V, but I figure that's what "UNREG" means. Everything else was within 1% of it's marked value (the regulated +50V was well within 0.5%).

The five unmarked test points read as follows:

next to INVERT switch: +34.06V
immediately behind A TRIG HOLDOFF: +14.64V
2nd back from A TRIG HOLDOFF: -2.411V
3rd back from A TRIG HOLDOFF: -3.776V
4th back, next to UNREG +50V: +137.9V

Until I find these in the service manual I have no way to know what they should read.

I did NOT check the -2450V point. I do not have a high voltage probe handy (though I probably have one somewhere). I figure that the CRT appears to be working correctly, so I can just assume that the high voltage power supply is working correctly (until I have a high voltage probe).

I have not checked ripple, but I plan to do that with my 2213 later today.


Re: TDS510a Power Supply

Derek Chauran
 

Thanks, as I mentioned, I am a novice at all of this, so it is very helpful to have pointers as to what to look into. I have been reading up based on your comments. Learning is exactly why I am here, and I have learned a lot.

For most of what I can imagine using the scope for, I will be looking at repetitive signals. E.g. checking power supplies for ripple, or observing simple, modulated RF signals (I'm a ham, which is where my interest in electronics stems from). In other words, I am primarily going to be looking at analog signals.

The 640a manual states that it has averaging, but not peak or high resolution.

I did a quick read on equivalent time sampling - the 640 has a higher sample rate (2g/sec) and interpolation, so the net effect is that both scopes claim an "effective" sampling rate of 100gsamples/sec, but the 640 has a better single shot bandwidth, and 2gs/sec on all 4 channels, whereas the 510a has 500ms/sec on 2 channels or 250ms/sec on 4.

The 510a definitely wins in sample buffer size - 50k vs 2k. That said, even Tek suggests that for most signals 2k is plenty.

Regarding peak, it looks like the 640a has envelope mode which is fine for repetitive signals, whereas peak is better for single shot? But that also means that peak is bandwidth limited on the 510a. Curiously I cannot find the non-interpolated real-time bandwidth of the 510a, the manual just says that it will decide when it forces interpolation or equivalent time sampling. I would assume that it's something like 125 mhz?

High res - also a clear winner in the 510a.

Thanks,
Derek
________________________________
From: TekScopes@groups.io <TekScopes@groups.io> on behalf of Siggi <siggi@undo.com>
Sent: Thursday, November 5, 2020 11:36 AM
To: TekScopes@groups.io <TekScopes@groups.io>
Subject: Re: [TekScopes] TDS510a Power Supply

On Thu, Nov 5, 2020 at 2:16 PM Derek Chauran <af7ux@outlook.com> wrote:

I am probably going to sell this scope, the 510 seems to sell for more
than the 640, even though the 640 looks like the better scope on-paper.
There are a couple of specs you should probably compare before you decide
which to keep and which to sell.

The sample buffer size might be a killer - you should compare the two,
especially as the TDS6XX don't have peak detect until the B-series (if
memory serves). Between a short record length and no peak detect, they can
be quite useless for slow captures.

I also don't think the TDS600s have averaging, nor hi-res, nor equivalent
time sampling.


Re: TDS510a Power Supply

Siggi
 

On Thu, Nov 5, 2020 at 2:16 PM Derek Chauran <af7ux@outlook.com> wrote:

I am probably going to sell this scope, the 510 seems to sell for more
than the 640, even though the 640 looks like the better scope on-paper.
There are a couple of specs you should probably compare before you decide
which to keep and which to sell.

The sample buffer size might be a killer - you should compare the two,
especially as the TDS6XX don't have peak detect until the B-series (if
memory serves). Between a short record length and no peak detect, they can
be quite useless for slow captures.

I also don't think the TDS600s have averaging, nor hi-res, nor equivalent
time sampling.


Re: Troubleshooting an old Tek 475

John
 

I wouldn't worry too much about all the Tantalum caps in the scope. There are rather a lot of them. You are unlikely to see them burned up. They just short internally. There are a handful in the power supply circuit between the various power rails and ground which is why I mentioned them and these can drag a line down if they are shorted. They are easily checked them with a multi-meter and can be replaced equivalent or nearest value electrolytic.

It is quick and easy easy to check the power supply outputs with a DMM. In approximately the centre of the main board, in between the bridge rectifiers and the cluster of 4 large metal can transistors, there is a group of test points with the voltages marked on the PCB. Page 171 of the pdf shows the board layout and page 172 the circuit diagram.


Making TDS 5xx/6xx elastomer buttons

Derek Chauran
 

Hello - I have a TDS 510A and a 640A, with only one set of buttons between them. I looked into buying set, but they are around $100 shipped, which is hardly worth the expense.

So I decided to use this as an opportunity to work on my CAD skills, and designed a set of buttons, and a mold for them. The plan was to 3d print the mold, and use RTV to cast the buttons with copper tape placed in the mold for the contact surfaces. This plan seems to be viable, except that my printer is having some issues and I cannot get it to print correctly right now. Is there anyone else who would be interested in collaborating on this effort? There's no money in it, and I plan to "open source" the files once I have finished.

Thanks,
Derek


Re: TDS510a Power Supply

Derek Chauran
 

Thanks Siggi! That cap is supposed to be less than 0.3 ohm, and I ordered a low ESR cap to replace it. I have ordered all of the parts to fix this, and I went ahead and ordered the caps to re-cap the whole thing. It costs me $8 to get stuff shipped from mouser, which is a good chunk of the cost for a full re-cap, and you can never have too many caps if I decide not to do it 😄. That said, the caps in the rest of the scope look really good. All of the solder joints are still nice and shiny, so I probably won't do the whole scope just yet.

I am probably going to sell this scope, the 510 seems to sell for more than the 640, even though the 640 looks like the better scope on-paper.

Thanks,
Derek

________________________________
From: TekScopes@groups.io <TekScopes@groups.io> on behalf of Siggi <siggi@undo.com>
Sent: Thursday, November 5, 2020 5:19 AM
To: TekScopes@groups.io <TekScopes@groups.io>
Subject: Re: [TekScopes] TDS510a Power Supply

On Wed, Nov 4, 2020 at 10:15 PM Derek Chauran <af7ux@outlook.com> wrote:

Oh, my, well, I think 7.2 ohm is a bit high for the ESR on that cap.

Yeah, this cap sees a fair bit of ripple current, so wants to be low ESR.
As this is in the standby supply, unless you turn off the hard switch at
the back, it'll be under stress 24/7.


The one next to it is around 1.6 too. i was going to re-cap the thing if I
got it working, but now am thinking I should just replace all of the caps
now. The big 450v cap looks maybe a tiny bit bulged.
So did mine, but it was perfectly fine. I don't think the DC bus bulk cap
is under a great deal of stress.


I also have a bu508a and my little tester says it's a resistor between the
collector and emitter, rather than a transistor, so that's bad as well.

That'd take down your standby supply for sure :).


Re: TDS784C ROMs

Steve Hendrix
 

Google turned up nothing related, so I look forward to hearing at least a few commands that will work. Thanks for the password, that's a start.

Steve Hendrix

At 2020-11-05 12:10 PM, Monty Montgomery via groups.io wrote:
The instructions in various places found by google searches work; any
working GPIB interface (I use a Prologix USB) works fine. No need for
a vintage model. Password 'rambo' and off to the races...
Let me search through my bookmarks for verbatim command lines in the
event Google doesn't help you, but I warn you, I'm on Unix...

Monty

On Thu, Nov 5, 2020 at 10:24 AM Steve Hendrix <SteveHx@hxengineering.com> wrote:

I've been lurking here for quite a while, and have seen lots of
discussions about saving the contents of the firmware ROMs in case
they degrade. I have programmers that go back to the early 80's, so
can probably burn a new set if I need to. Finding an old PC that can
run them might be problematic, but I still have an original IBM PC
with a full complement of interfaces, and it still works. However, I
can't find any instructions in the SCPI command set for this
instrument that will dump the images. Such a command is usually a
hidden function, not advertised to the world. Can anyone here tell me
how to dump the ROM images via GPIB?

Steve Hendrix






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