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Tektronic 466 - Storage Modes inop


Jim McIntyre
 

This is a new-to-me 466. It seems pretty much OK in non-store modes. When I pop it into variable Persistance, I still see the trace, but no storage. No effect from the View Time Storage Level, or Storage Intensity controls. Pushing Erase, blanks the trace for a second, but no flash of light, as I'd expect.


LV DC supplies all look OK.


Weirdest symptom follows: With the intensity turned all the way down, I see a few dimly lit, stationary 'spots' on the screen and a faint overall green glow.


No experience with tinkering at storage circuits... yet....


Comments, Ideas, admonishments, etc appreciated...


 

On 09 Mar 2016 18:46:03 -0800, you wrote:

This is a new-to-me 466. It seems pretty much OK in non-store modes. When I pop it into variable Persistance, I still see the trace, but no storage. No effect from the View Time Storage Level, or Storage Intensity controls. Pushing Erase, blanks the trace for a second, but no flash of light, as I'd expect.

LV DC supplies all look OK.

Weirdest symptom follows: With the intensity turned all the way down, I see a few dimly lit, stationary 'spots' on the screen and a faint overall green glow.
That is normal. I have noticed faint illuminated shadows and
illuminated dots before on storage CRTs.

No experience with tinkering at storage circuits... yet....

Comments, Ideas, admonishments, etc appreciated...
After checking the general stuff like the low voltage power supply
outputs and doing a detailed visual inspection, I would consider
connectors and socketted parts like transistors and ICs.

If that does not turn up anything, then I would do the z-axis
calibration procedures followed by the storage calibration procedures.


Ed Breya
 

I don't know if this will help, but it may be a good idea to let it cook for a few hours, especially if it hasn't been run in a few years. I have a 577 D1 storage type on which the display looks awful when first turned on, in storage mode, with a big pincushion green background that can't be turned off. After running for about twenty minutes, and a few erase cycles, it blanks out nicely.

If it doesn't settle down, you may want to check and tweak the flood gun circuits. Once the basic operation is confirmed, you can check the screen and storage mesh by filling the display - just set up for a free-running sweep, and work the vertical position up and down until the whole thing is written. Ideally, it should present a uniform filled green screen. You'll see any bad spots or after-images.

Ed


Tim Phillips <tim@...>
 

from Tim P (UK)
Aha !! The manual for the 5111 storage 'scope specifies a turn-on procedure for an instrument that has not been used for a while (2 wks) or from new.
With power OFF, Upper and lower store ON, brightness MAX, power up. This "reduces the ion content in the CRT" (from the manual), wait for the screen to flood. After 5 minutes ,do a couple of Erases, then U/L Store OFF. The full story is on pp1-4 of the 5111 manual, but, of course, I don't know whether this procedure is specific to the 5000 storage scopes or even that CRT.
Tim

----- Original Message -----
From: "edbreya@yahoo.com [TekScopes]" <TekScopes@yahoogroups.com>
To: <TekScopes@yahoogroups.com>
Sent: Thursday, March 10, 2016 3:54 AM
Subject: [TekScopes] Re: Tektronic 466 - Storage Modes inop


I don't know if this will help, but it may be a good idea to let it cook for a few hours, especially if it hasn't been run in a few years. I have a 577 D1 storage type on which the display looks awful when first turned on, in storage mode, with a big pincushion green background that can't be turned off. After running for about twenty minutes, and a few erase cycles, it blanks out nicely.

If it doesn't settle down, you may want to check and tweak the flood gun circuits. Once the basic operation is confirmed, you can check the screen and storage mesh by filling the display - just set up for a free-running sweep, and work the vertical position up and down until the whole thing is written. Ideally, it should present a uniform filled green screen. You'll see any bad spots or after-images.

Ed



 

The 5111 and 577 D1 both use bistable storage only. I've found the operation of (older) bistable storage systems mostly marginal. It is quite sensitive to temperature and periods of non-use but it does recover (mostly) after several hours under power.
The 466 has a different construction; it can benefit from being revived under power but far less so.

I have bistable storage 'scopes and several of the other types. I have always found that the non-bistable systems need far less recovery, like the 464, 466, 7613. I've seen the same differentiated behaviour in 'scopes using both systems, like the 7623A, 7633, 7834.

Bistable-only systems generally are older than the other systems, so with those, age may play a role in itself.

My 577 D1 and 5113 (bistable only, basically identical systems) need at least half an hour after being switched on to provide good storage. Scopes like the 464, 466 and 7834 just need a few minutes.

I think your 466 has a problem. Could just be a matter of voltage adjustments in the storage system.

Raymond


Jim McIntyre
 

First off, please forgive my mis-spelling in the title...

It was a typo, honest, I know how to spell Tektronix...


So, I've found a interesting hint. The 1.4V supply, which I guess is supposed to be regulated to 1.4V by Q2092/Q2094 is sitting at -1.8V all the time - even through an erase cycle. What I haven't figured out yet is what is supposed to source current into the 1.4V rail, as Q2094 appears to be a shunt regulator of sorts...


Jim McIntyre
 

Found 3 shorted transistors so far: Q1942, Q1944, and Q1948. Might be a few others in this area.

Any well-regarded cross reference for some of the Tek transistor p/n's?


Brian Bloom
 


Jim McIntyre
 

Perfect - Thanks!

I buzzed out the rest of the transistors and diodes across the A10 board, and found only one more - CR1947.


 

It would be nice to know what caused the failure. CR1947 is there to
prevent reverse breakdown of the base-emitter junction of Q1948.

I would also check for a shorted capacitor or open resistor.

On 12 Mar 2016 10:34:30 -0800, you wrote:

Perfect - Thanks!

I buzzed out the rest of the transistors and diodes across the A10 board, and found only one more - CR1947.


Jim McIntyre
 

Yes - It'd be nice to know what triggered this. Replacing these 4 parts has restored basic storage functionality. My best guess is there was a previous failed service attempt. There were some signs of this on the A10 Assy. Many of the adjustment pots are at one extreme, there is some flux residue around some of the jumper wires, and several of the TTL logic chips aren't original to the instrument.

There are still some issues, but variable presistence is now sort-of working, and the erase works. So I'm hoping it just needs adjustment now.


One valuable lesson I have learned is these TO-92 transistors do not have their base lead always bent the same way, so it's easy to get the E and C swapped if you're not paying attention...