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Yet another 7L5 issue (7L5 / 7854) below 10 kHz

Cliff Carrie
 

The dot frequency displays with the decimal point in the wrong place below 10 kHz (Fine mode on); the displayed number must be multiplied by 10. The 7L5 tunes correctly to 9.750 kHz, for example, but displays 0.975 kHz
Tek documented this in Service TekNotes in November of 1982. Strangely, they never produced or published a fix as far as I can discover. Does anyone have a solution, or ideas for one?

Cliff Carrie.

Re: 577 D1 function won't turn off

Mlynch001
 

Great information. Thanks for the update.
--
Michael Lynch
Dardanelle, AR

Re: 577 D1 function won't turn off

DW
 

I would like to make a correction it is NON storr that I adjusted not SENS COR

It is on the D1 storage board you will notice 4 blue dials grouped closely together, the second one over to the right, NON STORE is what resolved my problem

Re: 577 D1 function won't turn off

DW
 

I have an update

I performed the 370V calibration on TP 2 to ground from the D1 storage board. I was about 365 so i put it right at 370

I took pictures of the adjustments on the D1 board and very carefully moved each one slightly back and forth and noted the display.

I fixed my problem by carefully turning down SENS COR from the 3 o'clock position to near the 12 o'clock position, the ghosting problem disappeared and the D1 storage appears to work correctly and turn off when I don't want it. I turned off the instrument and back on, a brief flash of the screen but the display came on free of storage display artifacts

All the other settings are default except 370V and SENS COR

Hopefully this might help anyone out by trying this, maybe reply with your results to see if this is my particular case or perhaps it is a fix hopefully for some people

Re: 577 AC collector supply not reading zero on display

DW
 

Reading the manual I notice the following for the collector supply

120 Volts is fed to T101 autotransformer (Variable collector)

K125 turns T101 on or off

The wiper of T101 goes to what appears to be a filter L101 R101 and C101, and then it goes to the primary of T102

From T102 it appears this is where I get 6.5 25 100 400 and 1600V from for the collector

For 6.5 to 100V rectifier CR107 is used and above that CR103-106 is used

Since different rectifiers are used at higher volts I decided to test my problem at higher voltages, the problem appears to get much worse

At 1600V 8kOhms 5V Division 0 collector volts the line is 4 divisions across which should be 20V, not good

The collector supply appears somewhat simple if i look at certain sections of it. I feel like I simply have a T101 autotransformer issue. The wiper is making contact to the very edge but yet it acts like i have it turned up partially. Maybe a issue with T101 or maybe K125 or perhaps C101 is bad? I feel this problem is occurring at the beginning of the collector supply stage.

Re: Trying to save a 576

Mlynch001
 

I have a very early and a very late model 576. The CRT in the later one is an -05 at the end of the part number. The early one is a -00 or -01 if Memory serves me. The older one suffers from a bad HV transformer, which I am currently trying to get a replacement for.

--
Michael Lynch
Dardanelle, AR

Re: Trying to save a 576

Eric
 

On Sat, Dec 7, 2019 at 12:37 PM, Ed Breya wrote:


One more thing - it's possible that the intensity and focus pot string
resistors have drifted way out of spec. Depending on the circuit and drift
direction, you may not have enough range for intensity setting all the way up.
You'd have to study the circuit and make some measurements (they're elevated
to near cathode voltage).

Ed
CRT voltages tested at the neck pins.

1) -3815 Vdc
2) -3841 Vdc
3) -3840 Vdc
4) -2667 Vdc
5) NC
6) NC
7) 100 Vdc
8) 100 Vdc
9) 100 Vdc
10) 109 Vdc
11) 52 Vdc
12) NC
13) -3814 Vdc
14) - 3814 Vdc


Heater voltage ping 1-14) 5.9Vac

7L5 dot frequency reset bug - any clues or a fix?

Cliff Carrie
 

The 7L5 manuals say the Dot Frequency should reset to 0.000 kHz at power on. There have been previous posts about this not happening, but no mention of a fix. I have personally seen two 7L5s, including the one I am currently using in my 7854, that reset to a varying frequency near 3778 kHz. I have forced a reset using a jumper to trigger the power-on reset timer. The Dot Frequency goes to 0.000 kHz during the reset but goes back to 3778.xxx kHz when the reset timer ends. All other modes and indicators reset as expected. I don't think this is unique to the 7854 power on since the mainframe was already powered up before I did my test. I suspect a timing race in U830 as the reset pulse turns off. I know this is a minor annoyance, but the circuitry is there, and I'd like to make it work properly. My 7L5 service manual is 070-2184-01. The reset timer is Q621 on Drawing 5 lower left. U830 is on Drawing 8 (see pins 4 and 17).

1: Has anyone experienced this on the 7L5 in a mainframe other than the 7854?
2: Who else is experiencing this in a 7854?
3: Does anyone have a fix?

Cliff Carrie

Re: Trying to save a 576

Bob Koller
 

Eric,

Too bad the tube is weak, but very typical, I probably at least a dozen bad 576 tubes up in the loft, that I can't quite bring myself to toss.
You have the later HV transformer, so no worries there.
As for the dash number on the CRT, don't worry about that, all are usable, install any CRT that works!

Re: Trying to save a 576

Eric
 

Ryan, I would defiantly be interested in that especially if it has been in a box. The 05 is currently what is in there at the moment.

Re: Trying to save a 576

Eric
 

Bob you hit the behavior exactly square on the head. 0-75% intensity control the trace brightens then dims and brighten again and at full intensity it loses all resemblance of focus. So I think this tube is toast. Also this tube has a weird model number it is a 154-0563-05 I cant seem to find any reference to a tube version higher then 2. The High voltage transformer is the black silicone one.

Re: Trying to save a 576

Dave Voorhis
 

On 7 Dec 2019, at 21:18, Tam Hanna <tamhan@...> wrote:

on the risk of sounding like a broken record: please hang onto the DANAHER 576, 577 and 575 instruments with damaged screens.
Why do you call them _Danaher_ 576, 577, etc.?

I thought Tek wasn’t acquired by Danaher until 2007. Tek was still under independent ownership at the time the 575, 576, and 577 were made, wasn’t it?

If you’re naming it by current ownership, then wouldn’t it be more correct to call it Fortive?

Ownership often doesn’t reflect branding, anyway. E.g., a Vauxhall Corsa or Chevrolet Corvette is a Vauxhall Corsa or Chevrolet Corvette, not a General Motors Company Corsa or General Motors Company Corvette.

Or am I missing something here?

Re: Trying to save a 576

Tam Hanna
 

Hello,

on the risk of sounding like a broken record: please hang onto the DANAHER 576, 577 and 575 instruments with damaged screens.


Tamoggemon Holding k.s. currently is not in a position to make a public announcement re this, but we have something up our sleeve!


Tam

With best regards
Tam HANNA

Enjoy electronics? Join 15k7 other followers by visiting the Crazy Electronics Lab at https://www.instagram.com/tam.hanna/

Re: Trying to save a 576

Ed Breya
 

One more thing - it's possible that the intensity and focus pot string resistors have drifted way out of spec. Depending on the circuit and drift direction, you may not have enough range for intensity setting all the way up. You'd have to study the circuit and make some measurements (they're elevated to near cathode voltage).

Ed

Re: Trying to save a 576

Ed Breya
 

You may want to check that "intensify pulse" thing and circuitry to be sure it's working right. I don't recall if it should be active except in pulse mode. Speaking of which, are you sure you have the controls set up properly? Make sure it's not in pulse mode - there are buttons to select these, but I'm nowhere near a 576 right now, and can't see a panel to refresh my memory, so can't describe the right settings. You'll want it to be set for "normal" or "repetitive" or something like that.

If you figure out all the right operation, and the CRT is indeed very dim, it may be a candidate for rejuvenation, or replacement.

Ed

Re: Trying to save a 576

Ryan Scott
 

Hello, I have a 154-0563-05 CRT which came from the estate of a Tek collector.  I don't have a 576 so it's of no use to me.  You can have it for the cost of shipping from 97229 and take the gamble as it's in unknown condition.  Regards, Ryan Scott

On Saturday, December 7, 2019, 09:49:50 AM PST, Bob Koller via Groups.Io <testtech=yahoo.com@groups.io> wrote:

Dennis, no other instrument used the 154-0563-xx CRT, unfortunately.

Re: 577 D1 function won't turn off

Dave Voorhis
 

Thanks for the tips, and I will try the storage calibration when I get a moment.

Incidentally, I also have some analog storage Tek scopes — a 549, a 7623, and a 564.

The 549 is in excellent condition and works well including most of the storage capability. I say “most” because the enhanced mode has stopped enhancing. I’ll have to look at that when I get a moment. The CRT seems a tad dim but entirely usable. I haven’t investigated whether the dimness is due to a worn CRT, a bias or Z-axis issue, inherent in the design, or some/all of these together.

The 7623 is usable but in need of general cleaning and fettling, though the storage facility works. Storage mode is rather low-contrast — apparently a characteristic of its design — but works well and the variable persistence is very useful.

The 564 is unrestored and has various issues, and the storage facility clearly needs adjustment but works (-ish) once it’s warmed up.

None appear to have the storage target burn-in that’s apparently characteristic of all of these, so I guess I’m fortunate in that respect.

I also have two digital storage ’scopes — a 7D20 in a 7603 mainframe that’s currently down due to power supply issues, and a 222 portable that works and looks like new though the original lead-acid battery is kaput.

So much to work on, when time permits. :-)

On 7 Dec 2019, at 18:51, Dennis Tillman W7PF <@Dennis_Tillman_W7PF> wrote:

Hi Dave,
I have probably used at least fifty Tek scopes in my lifetime but fewer than five storage scopes or curve tracers. The first time I tried using storage was on an almost new 549 in 1968. I remember thinking to myself that storage was better than nothing at all but it wasn't all I hoped for. Two things contributed to that impression: The stored traces would bloom, and the storage was hard to control. In the years since then I have learned to settle for what I get on Tek storage scopes instead of being pleased with the results.

I use my 577-D1 a lot and I frequently need to store the results. At one point I got annoyed with the results and decided that calibrating the storage circuitry according to the manual could only improve things. Since this was the first time I ever adjusted a storage scope I cannot say whether the directions were confusing to follow or whether I found them confusing. I was also surprised that many of the adjustment steps seemed to interact with each other or seemed to do nothing at all. After doing the best I could to follow the written directions it was hard to tell that I had made much difference at all. At that point I just ignored the directions as I tried adjusting the pots for what I thought was the best result.

Looking back there are several possible explanations for why I wasn't able to improve my 577-D1 as much as I had hoped.
1) I have limited experience with storage technology.
2) I don't understand the limitations of storage technology.
3) My expectations for storage are unrealistic.
4) I did not understand the calibration procedure.
5) I have a problem following directions (a recurring issue in my life).
6) The particular CRT I was trying to adjust was getting old or worn out.

I do know enough about storage that it is important to go through the cal procedure when you change the CRT. The cal procedure shouldn't take you as much time as it took to change the CRT. It may provide answers to at least some of the things I listed above. I'm starting to think that if I can find the time it would be worth recalibrating my 577-D1 storage again.

Dennis Tillman W7PF

-----Original Message-----
From: Dave Voorhis
Sent: Saturday, December 07, 2019 9:45 AM
Subject: Re: [TekScopes] 577 D1 function won't turn off

It is a used CRT that the previous owner was told was extracted from a working unit, though “working” may or may not have included storage. The previous owner of my 577 didn’t know.

And that’s the reason for my question — before I (eventually) launch into storage calibration, I want to know whether or not it’s reasonable for the storage calibration settings that work for one CRT not to work for another. If it's typical for D1 CRTs to be interchangeable and the storage to essentially work — though perhaps not optimally — I’ll keep my eye out for another replacement.

Instead, if it’s typical (or at least reasonable) for changing the CRT to result in non-storage condition then I'll only look for a replacement CRT once I confirm it’s defective, if it is. ‘Erase’ does appropriately “green" the screen so I presume at least the flood guns are working.

On 7 Dec 2019, at 17:34, Dennis Tillman W7PF <@Dennis_Tillman_W7PF> wrote:

Hi Dave,
Was the replacement CRT a new CRT? If not new how do you know it was any good in the first place?
Dennis Tillman W7PF

<SNIP>
-----Original Message-----
From: Dave Voorhis
Sent: Saturday, December 07, 2019 4:47 AM
Subject: Re: [TekScopes] 577 D1 function won't turn off

I have a 577 D1 that came with the original but weak CRT installed and a replacement CRT in a box. Storage mode on the original weak CRT worked well, but the primary trace was almost too dim to see.



--
Dennis Tillman W7PF
TekScopes Moderator


Re: 577 D1 function won't turn off

Siggi
 

On Sat, Dec 7, 2019 at 1:16 AM Dennis Tillman W7PF <@Dennis_Tillman_W7PF>
wrote:

The other one is the storage Brightness knob doesn't seem to do anything.
On my new-to-me 577 the storage brightness knob only works when the
collector supply is turned down as near zero as makes no difference.

Re: 577 D1 function won't turn off

 

Hi Dave,
I have probably used at least fifty Tek scopes in my lifetime but fewer than five storage scopes or curve tracers. The first time I tried using storage was on an almost new 549 in 1968. I remember thinking to myself that storage was better than nothing at all but it wasn't all I hoped for. Two things contributed to that impression: The stored traces would bloom, and the storage was hard to control. In the years since then I have learned to settle for what I get on Tek storage scopes instead of being pleased with the results.

I use my 577-D1 a lot and I frequently need to store the results. At one point I got annoyed with the results and decided that calibrating the storage circuitry according to the manual could only improve things. Since this was the first time I ever adjusted a storage scope I cannot say whether the directions were confusing to follow or whether I found them confusing. I was also surprised that many of the adjustment steps seemed to interact with each other or seemed to do nothing at all. After doing the best I could to follow the written directions it was hard to tell that I had made much difference at all. At that point I just ignored the directions as I tried adjusting the pots for what I thought was the best result.

Looking back there are several possible explanations for why I wasn't able to improve my 577-D1 as much as I had hoped.
1) I have limited experience with storage technology.
2) I don't understand the limitations of storage technology.
3) My expectations for storage are unrealistic.
4) I did not understand the calibration procedure.
5) I have a problem following directions (a recurring issue in my life).
6) The particular CRT I was trying to adjust was getting old or worn out.

I do know enough about storage that it is important to go through the cal procedure when you change the CRT. The cal procedure shouldn't take you as much time as it took to change the CRT. It may provide answers to at least some of the things I listed above. I'm starting to think that if I can find the time it would be worth recalibrating my 577-D1 storage again.

Dennis Tillman W7PF

-----Original Message-----
From: Dave Voorhis
Sent: Saturday, December 07, 2019 9:45 AM
Subject: Re: [TekScopes] 577 D1 function won't turn off

It is a used CRT that the previous owner was told was extracted from a working unit, though “working” may or may not have included storage. The previous owner of my 577 didn’t know.

And that’s the reason for my question — before I (eventually) launch into storage calibration, I want to know whether or not it’s reasonable for the storage calibration settings that work for one CRT not to work for another. If it's typical for D1 CRTs to be interchangeable and the storage to essentially work — though perhaps not optimally — I’ll keep my eye out for another replacement.

Instead, if it’s typical (or at least reasonable) for changing the CRT to result in non-storage condition then I'll only look for a replacement CRT once I confirm it’s defective, if it is. ‘Erase’ does appropriately “green" the screen so I presume at least the flood guns are working.

On 7 Dec 2019, at 17:34, Dennis Tillman W7PF <@Dennis_Tillman_W7PF> wrote:

Hi Dave,
Was the replacement CRT a new CRT? If not new how do you know it was any good in the first place?
Dennis Tillman W7PF

<SNIP>
-----Original Message-----
From: Dave Voorhis
Sent: Saturday, December 07, 2019 4:47 AM
Subject: Re: [TekScopes] 577 D1 function won't turn off

I have a 577 D1 that came with the original but weak CRT installed and a replacement CRT in a box. Storage mode on the original weak CRT worked well, but the primary trace was almost too dim to see.



--
Dennis Tillman W7PF
TekScopes Moderator

Re: Trying to save a 576

Bob Koller
 

Dennis, no other instrument used the 154-0563-xx CRT, unfortunately.