so in a nutshell,is my scope triggering iffy?
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Looking at the pictures of the front panel controls on TekWiki, and reading the manual, it sounds like the 453 only supports triggering on Ch 2 in the NORM trigger mode selected by the TRIGGER control between the two vertical input clusters. Reading further into the manual (and looking at the front panel images for some versions of the 453) seems to indicate that internal trigger is only available on Ch 1. There is some talk about the NORM mode triggering from the displayed channel, but I don't see where or how that is implemented, and there is specific language in the circuit description section that indicates that Ch 2 does NOT have trigger pickoff.
You may need to calibrate your understanding and expectations of this scope.
-- Jeff Dutky
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can no one shed any light on this?,it seems odd to need a signal on chan A to be able to trigger on chan B input,or am i missing something?
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Re: Thinking on CRT restorations for double peaking tubes.
it would be good to know with mechanically intact tubes:
a) are there any other problems with tubes other than leaks, being gassy or double peaking?
b) is there any evidence of issues that can be seen from the outside?
If a tube is gassy, isn't it the case that a very small quantity of air comes through the glued joints/points (front / middle / rear)?
If that is true, could it be possible to seal those joints/points with glue (e.g. epoxy resin / superglue / 2-component methyl methacrylate)?
The best glue should gas out as little as possible. (To be determined.)
In the other case, the gases would be emitted internally.
Tube contacts are bend sometimes due to incorrect handling. Maybe you need to straighten them before further use. Can that make a tube gassy?
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Re: Need Help With Tek 453 Weird Problem
I have made progress on one of the issues. The instability on start up, that was due to the wrong transistor being used for Q1189. The transistor that was in there apparently could not handle the voltage it was seeing (the data for it sheet said it was rated for only 75V). Manual says that a 2N5184 is a replacement for Tektronix 151-0250-00 but I don't have any of those lying around but I did have an NTE equivalent (NTE 128) from my donor scope, so I put it in there to see what happened. Now it's stable from the second I turn it on! Interesting because Q1189 is really only there for short circuit protection, but I guess because it's connected to the regulated 75V and unregulated 150V supplies, it must mess with all of the circuits connected to those power supplies until it warms up.
The weird fishbone thing is still going on when in MAG and EXT HORIZ modes though. I tried to get a good video of it but my iphone won't sync well and the video is terrible but here is a 10 second video showing two pictures of it. It travels cyclically from left to right along the waveform. Don't worry, the CRT isn't as bad as it looks, its just my makeshift CRT cover made from a cassette tape that my iphone can't get a good picture of either. I need to get one of those original smoke grey CRT covers but they seem to be non-existent items on ebay. :-(
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Re: Thinking on CRT restorations for double peaking tubes.
I have 3 CRT's in the lab one out of a 577 and 2 out of a 576, I am willing to experiment on the 577 tube as it can readily be replaced. I do not want to risk a 576 tube until things have been tested and proven. Given the power supplies available to me as well as having an SMU in the lab I believe I have enough control over the equipment to do some testing. My current thoughts are drive the heater pins with a power supply and grid the grid with the SMU. There will be no deflection or brightness given that there is no acceleration voltage however I would be able to get a good reading on grid current direct from the SMU as well as gets some plots. That might shed some light on things.
I believe the goal is the burn off the upper layer of cathode coating to allow the tube to begin emission again. On close inspection of a double peaking tube I do not see the other indicators of the envelope being gassy however this was done with an uncalibrated eyeball and no magnification.
Using the 2450 SMU would give me very fine control of the grid currents I could also do a voltage sweep on the grid from - voltage to something + and plot current this might give a clue as to what is causing the double peak.
I was here for the discussion a year ago. But I will also admit I have a soft spot for the 576 and don¡¯t want to see these units die if I can help it.
Zen
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-----Original Message----- From: [email protected] < [email protected]> On Behalf Of Jeff Dutky Sent: Thursday, April 7, 2022 12:08 AM To: [email protected]Subject: Re: [TekScopes] Thinking on CRT restorations for double peaking tubes. Zen, I think the consensus was (last time this was discussed, about a year ago) that double peaking is the result of irreversible damage to the cathode coating. I'm not saying that the consensus is to be taken entirely at face value, as I don't think that complete investigation was done fully verify the claimed failure mode. I suppose, if you had a ready supply of verified double peaking CRTs, and the willingness to destroy them, you could extract their cathodes and compare them under magnification. If I recall correctly, there were other commenters who thought that double peaking was due to the CRT becoming gassy, and I had some hope that that was the correct diagnosis (because I have a 5103N that appears to be double peaking, and, at the time, I had no replacement CRT. Also, the 5103N seems to display less double peaking if you actively use the scope for a few days, which suggests that it might be gassy, and usage is allowing the getter to consume more of the gas). Still other commenters said that the double peaking could be addressed by some kind of rejuvenation process like you are planning, but that the double peaking returned within a few months to a year. My take, based on very little evidence, is that double peaking may actually be several different failure modes, each with slightly different treatments and morbidity. I think that the rejuvenation process may have been performed in-scope, rather than with an external instrument. -- Jeff Dutky
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Hi , I would be interested in a set for my TDS744 -- original version of scope .
Thanks in advance .
Brian (UK)
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On Thursday, 7 April 2022, 06:19:41 BST, mystic96 <clbarber1@...> wrote:
Looking for feet for my new scope, does anyone have suggestion or can print them?
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what is a,744a, not a tektronix number
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Yes i found one there.,never gave that a thought.thanks.
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Hi i have a 453 with triggering issues,This 453 seems to trigger fine with an input on cha (ie the call signal),chb wont trigger unless i have a T piece and feed the call input to both bnc's ch a+b,it wont trigger on ch b unless a has an input also from the call bnc,is that normal,thats with trigg set to internal,also if set to line the waveform moves slowly across the screen,but is ok set to int,any ideas?,i have changed ch a tunnel diodes ans a few resistors and caps as it was suffering from old age and wouldnt trigger on ch a,also cleaned the switches,A is now working b doesent unless cha is fed a signal too.
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Looking for feet for my new scope, does anyone have suggestion or can print them?
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Re: Thinking on CRT restorations for double peaking tubes.
Zen,
I think the consensus was (last time this was discussed, about a year ago) that double peaking is the result of irreversible damage to the cathode coating. I'm not saying that the consensus is to be taken entirely at face value, as I don't think that complete investigation was done fully verify the claimed failure mode. I suppose, if you had a ready supply of verified double peaking CRTs, and the willingness to destroy them, you could extract their cathodes and compare them under magnification.
If I recall correctly, there were other commenters who thought that double peaking was due to the CRT becoming gassy, and I had some hope that that was the correct diagnosis (because I have a 5103N that appears to be double peaking, and, at the time, I had no replacement CRT. Also, the 5103N seems to display less double peaking if you actively use the scope for a few days, which suggests that it might be gassy, and usage is allowing the getter to consume more of the gas). Still other commenters said that the double peaking could be addressed by some kind of rejuvenation process like you are planning, but that the double peaking returned within a few months to a year.
My take, based on very little evidence, is that double peaking may actually be several different failure modes, each with slightly different treatments and morbidity. I think that the rejuvenation process may have been performed in-scope, rather than with an external instrument.
-- Jeff Dutky
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Thinking on CRT restorations for double peaking tubes.
I have a few tubes in the back room that are double peaking now and I was reading a few things on line, which is dangerous I know. but it got me thinking would 2 SMU units be able to do a tube restoration. I know these units are not easy to come by but I have a very stable power supply that can drive the heater pins. I also have access to a Keithly 2450 in the lab. This can supply 100ma up to 200 Vdc as well as be able to exactly time the pulses. It also gives me dial a current control down to 6 decimal places of accuracy. as well as full control of the timing and number of repetitions. From a quick rolling it around in my heat this seems like it might be able to help a tube with cathode poisoning.
2 of the double peaking tubes I have are 576 tubes so if this works it would be very valuable in keeping these units alive and well.
Zen
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Have you taken a look at what's available at tekwiki?
--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070
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On 4/6/2022 17:08, nanovnauser@... wrote: Hi all,i am trying to find a manual to repair my 453,its a later fet model not the A verson,can anyone point me where to download it from?,tia.
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Re: (7854) A Drop-In Replacement for the MCM68766 EPROM
I wonder if any lawsuits over the similarity in names.? MOSTEK? MOS TEK? verses MOS Technology.? I remember Commodore had very fast turnaround when upgrading design on their color chip because they bought a semiconductor company.? I didn't follow the details.? A company I worked for had a threat of lawsuit because of similar names.
Carl Hallberg
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On Wednesday, April 6, 2022, 06:10:19 PM CDT, Michael A. Terrell <terrell.michael.a@...> wrote: Commodore used MOS Technology chips, since they owned the company. On Wed, Apr 6, 2022 at 5:46 PM Carl Hallberg via groups.io <n9ess= [email protected]> wrote: Sorry about an error in the flat pack chip I'm looking for.? I wrote
TA7761P and should be TA7761F.? Off topic.
Carl Hallberg (W9CJH)
On Wednesday, April 6, 2022, 12:02:35 PM CDT, Carl Hallberg via groups.io
<n9ess@...> wrote:
I have a whole tube of mcm68764L eproms.? If these can replace the proms,
I will mail 5 to someone who can and wants to program them.? I cannot find
data sheet on Google, so don't know specs.? One of the eproms of the 5 I
did attempt to program and may or may not have been damaged.? That is why 5
of them.? I also have mcm68766,? but may need them (or some) in the future
for Tek, HP?? Will mail to contiguous United States. You pay postage.? I am
looking for 2 Toshiba TA7761P.? The description on internet is wrong, so
never attempted to purchase.? Used in radio control.
By the way Raymond, the roms in the Commodore 64 were also Mostek.? Maybe
why some of the failures.
Carl Hallberg (W9CJH)
On Wednesday, April 6, 2022, 10:33:35 AM CDT, Dave Wise <
david_wise@...> wrote:
The extra hardware for patching consisted of an FPLA (Field-Programmable
Logic Array) and a PROM.? The FPLA monitored the address bus, and on
certain ranges it rerouted Chip Select from the mask roms to the patch
rom.? From the processor¡¯s point of view, this replaced a couple of
instructions with a jump that led to replacement code in the PROM, which
did its thing then jumped back to the mask ROM.
This scheme was used in 1980 in the 4024/4025/4027 terminals made by the
Information Display Division at the Wilsonville plant.? Later models used
EPROMs, 2732 and up if I recall correctly.
Dave Wise
IDD 1980-1995
From: [email protected] <[email protected]> On Behalf Of Raymond Domp
Frank via groups.io
Sent: Tuesday, April 05, 2022 8:08 PM
To: [email protected]
Subject: Re: [TekScopes] (7854) A Drop-In Replacement for the MCM68766
EPROM
On Wed, Apr 6, 2022 at 04:41 AM, Carl Hallberg wrote:
The MCM68766 can always be replaced by a 2764 using a 28 dip socket to
24 dip
header.? I don't have a 7854 and didn't look up the specs, but need to check
the access time.
Physical space is the problem here, not electrical specs; the four 24-pin
ROMs are mounted end-to-end lengthwise with only 0.2" in between, which
doesn't allow for the longer 28-pin 2764's. on standard converting headers.
The two rows of two each that make up the total of four ROMs are 0.3"
apart. There would be enough space if one built a flat plug-in piggy-back
PCB and mounted the replacement EPROMs without sockets.
Standard MCM68766's (Ta <= 450ns) will do the job. I used them in one
7854. The bad IC's are not EPROMs (as Ram says) but mask ROMs, made by
Mostek. Some 'scopes are equipped with Motorola mask ROMs. Those don't
suffer from "ROM-rot". BTW, the board contains extra hardware that allows
patching of data in address ranges read from the ROMs, probably because it
was considered too slow and expensive to run new masks if a change was made.
Raymond
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Hi all,i am trying to find a manual to repair my 453,its a later fet model not the A verson,can anyone point me where to download it from?,tia.
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That center pin was difficult for the final assembly people too. Later in the 7000 series life, manufacturing engineers identified as many Peltola GND sockets as possible that could be rotated for better visibility of the center conductor. Any time a board was in revision for other reasons, the mfg engineer would press to have the socket reoriented or relocated for better visibility. You can see the center conductor during insertion on many of the later boards by looking through the split in the GND portion of the connector. A keen eye, a flash light and a very flexible neck can help you avoid missing the target.
Another failure is loose braid that touched the center socket. Considering the quantity of connections and unit cost of a few pennies, the margins more than covered the rework expense. A simple looking invention that probably made millions of dollars.
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diyguitarist
Brian
Jean-Paul