That's what I was thinking; that they may have run the heaters off DC to prevent hum and it would be easier to supply 150mA heaters than 300mA in the tube era. Now it would be simple to use a three terminal regulator IC to provide 6.3 volts.

Don Black.

David,

More below:

Because I was unsure of where to take readings on the caps as they
appear to have four pins, I took scope ripple readings from P890
connector on the A10 rectifier board. I hope this was OK. With probe set
on X1 and AC setting, I measured a max ripple of about 0.5 Volts P/P on
P890-1/5/2/ P890-4 was quite flat, I couldn't hardly measure any ripple.

Your ripple measurements sound OK, so your filter caps are most-likely good. Just remember many of the supplies are not up to normal output voltages, so their output currents are lower than normal, and therefore, ripple on the filter caps will be lower than during normal operating conditions (good or bad caps). The outer pins are the - pins and the center-most pin is the + pin.

On pins 6 and 7 of the 130 volt section, I wasn't able to measure the
ripple on the 250uF cap because I couldn't get my scope's two channels
to be in sync.

I should have also said to use Chop mode. I think you must have been using Alt (alternate) mode. Also, I should have said that once the +50V supply is working, you can measure ripple on C806 via single-ended (referenced to ground) using one probe only, like the other caps. You'd want to be using a 10X probe, espescially if your using DC coupling.

I did manage to take some voltage readings from the 130
volt section though. Voltages on Q850, VR851, and Q852 were all minus
about 30volts instead of plus 50 volts.

That's probably OK, since the +50V supply is dead, and you're basically measuring the negative side of the bridge rectifier and cap (C806).

The proper fuse in this line has
been replaced at some time in the past with a different style in-line
type fuse holder and hooked up to the original fuse "prong type
holders", so it looks like there might have been a problem with this
section in the past. Do you think that these minus readings indicate
that the AC hasn't been rectified properly and that there might be a
problem with the diodes?

David.

Back to the +50V supply: It's a little risky, but I'd suggest to remove Q876, monitor the +50V output with your DVM, and power-up the scope. If you're lucky, the +50V supply will come up to normal. Q876 is the current sense differential amp. Its job is to cut back the output voltage if the current through R875 (1 ohm), and thus the +50V supply's output, gets too high. This could happen because of for example a shorted cap somewhere else in the scope. I'm thinking the "B" trasistor has a C-B short, but that's just a guess.

Maybe you want to get someone else's opinion before you do what's suggested above.

You could also remove and check both transistors in Q876 with a diode-check function on a DMM. The scope could remain off.

Also, it might would help if you could mark-up a hard copy of the schematic with all of your voltage readings so far, scan it in, and post it somewhere for us to see. I'd suggest to use a red pen (red for bad). Mainly just the +50V supply section is needed.

Jimmy

¿ªÔÆÌåÓý

?

Tek W Plugin 100-3269, mod kit 040-0447-00: ...improves overdrive recovery characteristics...

?

Just?"found"?this?NIB mod kit dating from 1971, complete with pre-stuffed gold pcb, matched transistors?and other components, even silver solder and hookup wire -?sealed in compartments of a plastic bag.

?

Later?W's incorporated this mod, so I think I'll preserve this kit?as is.

Let me know if anyone would like to see pictures.

Bernd Schroder

?

?

In a message dated 1/24/2012 6:10:23 A.M. Pacific Standard Time, ataylor@... writes:

Low phosphor response or fast decay shouldn't be as much trouble if you can mount some UV LEDs inside the hood so they can be left on continuously during the shot, or right up to it if there's visible interference. If you use a color camera it should be blind to any true UV reflections - but not necessarily the "visible" part of deep blue or near-UV emission. These cameras usually have bandpass filters so the white balance won't be upset by UV or IR illumination. Some experimenting should be able to assess the camera response. If there's a problem it may be possible to cascade another white balance filter (since true color response isn't needed) to sharpen the passband edges, or a filter that will pass mostly the phosphor emission wavelengths but block the rest.

Ed

On 25/01/2012 00:20, Jochens Feldhaar wrote:

to read your messages, I always have to leave my Thunderbird standard
display and call the source text, there your message is OK and readable,
but for some reason it will not appear in the normal message text window.

They get flagged as spam by my server which runs Spam Assassin.

Try sending in plain text rather than html.

Gordon

¿ªÔÆÌåÓý

Hello Heinz-Peter,

to read your messages, I always have to leave my Thunderbird standard display and call the source text, there your message is OK and readable, but for some reason it will not appear in the normal message text window.
Just my 0.02€ cents.....

Regards, Jochen DH6FAZ

Am 25.01.2012 01:06, schrieb Heinz-Peter Deutsch:

¿ªÔÆÌåÓý

On 23/01/2012 03:08, jtjewell83 wrote:

?

David,

More for you below. Hope it helps:

> >
> > Could also be C866 is shorted, but that would be extemely rare.
> > To eliminate that, pull one side up temporalialy, and power up and
> > re-measure R860 volts.
> >
> +69V with ref to ground.

I think you measured the "high" side of R860(the 130V supply line). Maybe I should have said measure the collector of Q860; this is the same as the base of Q869 and the low side of R860; or should be if connections are OK. Again, this would be with one end of C866 lifted.

>
> I must thank you for your persistent help so far Jimmy, very explicit
> instructions that are very easy to follow!

Thanks.

>
> re cap ripple testing, do I put scope probes only on the cap pins of
> each individual cap to test each cap?

First, did you see my earlier posting about measuring ripple with an old analog meter that has an "OUTPUT" terminal? Anyway...

Hello Jimmy.
Yes , sorry that I didn't reply to your question. The answer is that I do not now have an analogue meter at all!

Here's how I would check for excessive ripple using another (test) scope. This will work for all of the big filter caps that have one terminal connected to chassis ground. DO NOT use this method for the filter cap (C806) in the 130V supply because neither one of its terminals is connected to chassis ground:

<<<<<>>>

1. Ground a 10X probe hooked to the test scope to chassis of problem scope. Use a good-quality clip lead to extend the probe's ground lead if the length of the ground lead is not enough for easy measurements, AND INSULATE the 2 alligators' connection with some black electrical tape so this won't short something out if it accidentally touches anything.
2. Set test scope channel to 50V/div. (Use 5V/div if you've got a scope that does not auto-sense probe attenuation). Be sure to use a 10X probe.
3. Set test scope channel to AC coupling and vertically center the sweep. (You can initially use DC coupling if you want to see the DC component also.)
4. Set test scope for Line trigger, and about 10mS/div. Adjust trigger for a steady sweep (flat line when probe tip is not connected to anything).
5. Carefully probe the "hot" side of each big filter cap. For most, the "hot" side is the "+" terminal. However, for some like C808 (1800 uF) for the -50V supply, it would be the "-" terminal.

If the cap is good, you should see a sweep that's still nearly flat. I'm thinking no peak-to-peak waveform on a filter cap should be more than about 3V. If necessary, increase vertical sensitivity to 5V/div, or less, so V peak-to-peak can be more accurately measured. You DON'T won't to overdrive the test scope's channel amp by using too much sensitivity (As a general rule, don't let the waveform go vertically too much off the top/bottom of the screen.) It is good to return the test scope's channel to the 50V/div before going on to the next cap!!!!!

To check filter cap C806 in the 130V supply use two 10X probes, two scope channels of the test scope, set one channel for "Invert" and use the "Add" vertical function. Make sure both channels have equal V/div settings, and they are adjusted for equal gain. This is basically a differential measurement. To verify test scope's settings (equal gains, etc.), probe a common signal point with both probes and make sure there's no (or very little) signal/ripple.

It will be good to post your ripple measurements.

Because I was unsure of where to take readings on the caps as they appear to have? four pins, I took scope ripple readings from P890 connector on the A10 rectifier board. I hope this was OK. With probe set on? X1 and AC setting, I measured a max ripple of about 0.5 Volts P/P on P890-1/5/2/???? P890-4 was quite flat, I couldn't hardly measure any ripple.
On pins 6 and 7 of the 130 volt section, I wasn't able to measure the ripple on the 250uF cap because I couldn't get my scope's two channels to be in sync. I did manage to take some voltage readings from the 130 volt section though. Voltages on? Q850, VR851, and Q852 were all minus about 30volts instead of plus 50 volts. The proper fuse in this line has been replaced at some time in the past with a different style in-line type fuse holder? and hooked up to the original fuse "prong type holders", so it looks like there might have been a problem with this section in the past. Do you think that these minus readings indicate that the AC hasn't been rectified properly and that there might be a problem with the diodes?

David.

Regards,
Jimmy

mmh, the second time a text vanished ?

In my own (yahoo) return copy, the text was there.
After i tried to send the text again? - gone ???
strange behavior ...
-------------------------------
Ok, here it come again:

i said, why you don't use empty (blind) panels


Peter

"Dennis Tillman" <dennis@...> wrote:

This doesn't help me with the 577/D1 which has a different phosphor that
doesn't glow much or for very long with the LEDs I have tried so far.

I just tried banging on mine (with the filter off) using
a big old Honeywell Strobonar that used to hang on a press camera.
I've no doubt I fed it a bunch of UV. Looks like the bistables
don't do so well. P31 & P7 both hang in there beautifully.
-ls-

You might want to purchase this:

?

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Ed, Brad

I didn't think about the plastic in front of the CRT. Removing it makes the
7934 storage CRT glow nicely. Removing it from the 577/D1 makes the phosphor
glow faintly in PURPLE! I didn't expect that. The characteristic curves show
up in green on this curve tracer so is this CRT coated with two or more
phosphors?

This is getting complicated. There are short persistence phosphors and long
persistence phosphors responding on some of these CRTs.

It would be good to hear from a Tek Phosphor expert about all this.

But maybe others will give it a try with other color LEDs on whatever scope
they have since it is so easy to do.

Dennis

Hi Brad,

Correction to my original post where I said:
"The other LED I tried was a 485nM one I just got."
I meant so say:
"The other LED I tried was a 385nM one I just got."

385nM is considered purple/UV by the LED folks. It isn't that far into the
UV so it still has some visible light coming out of it. It looked a not so
bright white to my eye. The first LED was 394nM which is only 10nM apart on
the spectrum but it was listed as very bright. It looked to be bright blue
to my eye. The brightness might have had more effect on the CRTs than the
difference in wavelength.

I also tried an IR LED. It was unimpressive. I did not try red, green,
orange or yellow LEDs. There are just too many combinations of LEDs, CRTs,
phosphors, and who knows what else, affecting the results.

Based on my seat-of-the-pants experiment this is a promising idea. In the
end, I doubt that there will be a single LED that works for all CRTs. I
encountered far too many variables to reach a definitive conclusion. More
experimentation with different LEDs and different CRTs is needed. I think
the least of the problems will be where to place the LEDs.

Dennis

Jerry,
why you don't use empty (blind) panels ?

Peter
=============
Hi,

--- In TekScopes@..., "Nick" <nick@...> wrote:

My AFG5101 has started saying "battery low" when powered on - is that an easy thing to change?

Ordered a service manual, however it looks like a Lithium module on one of the end boards - made by Renata and marked 3V and "125-1". I can't find a data sheet for this thing, but I think its actually an encapsulated CR2032 with a couple of 1N4148 diodes - Renata make a similar module called a "175-0", but the "-0" means no internal diodes - they don't make a "175-1" - the suffix "-1" indicates internal diodes - they make a "1000-1" but its too big, however I'm pretty sure its functionally identical, so I can use its layout - I'll check the existing module once I've de-soldered it...

I think its going to be easier to make a carrier with a coin cell holder for the 2032 and the two diodes - easier to change the cell in the future too...

Also, the LCD contrast is very poor, as is the viewing angle - is there anything I can do about that?

Still hoping for an answer on this...

Nick

Yes, UV LEDs are the way to go. The old school cameras we discussed had plenty of UV from actual UV lamps, or the high UV content from a xenon flash. The other variable is the UV loss in the plastic layers in front of the CRT. UV LEDs should be readily available. I bought some in the form of small keychain flashlights from a surplus store years ago - there should be even better and cheaper ones around now.

The intense blue LED wavelengths work fine for the modern "white" LED phosphors, but apparently not so much for CRT ones.

Ed

To be honest I didn't think of that possibility. Anyway, there was a lot to learn from such a silly bad contact.
Albert

On 1/24/2012 12:38 PM, Dennis Tillman wrote:

During the discussion of the 576 vs 577 curve tracer I mentioned the 577
graticule was not illuminated which I find annoying every time I want to
take a picture of device characteristics on the CRT.

Later I realized I might be able to take advantage of the storage CRT
flood gun on my 577 D1 to light the screen from inside the CRT. It is
not the solution I was looking for but it does work (with drawbacks).

A more intriguing solution came from Ed Breya, with an explanation of
how it works from David. If you ???flash??? the phosphor it will glow and
illuminate the graticule from inside the CRT. I tried this with two
different LEDs I had handy and the results were quite promising.

<snip>

Hello, Dennis--

Have you tried using ultraviolet-emitting LEDs? IIRC,
one of the --HP-- oscilloscope cameras used a UV emitting
lamp to light up the screen's phosphor and show the graticule.

73--

Brad AA1IP

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Take care when you test power supply.I had repared 4 Tek475.
But with the last something wrong occured the K tube filament burned!!!Something I d never explained as I have more than 40 years experience!