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The following photos have been updated in the SC504 Trace Problem ( /g/TekScopes/album?id=300558 ) photo album of the [email protected] group.

* IMG_2541.jpeg ( /g/TekScopes/photofromactivity?id=3896193 )

*By:* Barry Breaux <groupsio@...>



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Barry Breaux <groupsio@...> updated the photo album SC504 ( /g/TekScopes/album?id=300558 ) : SC504 photos

I'd like to build Dennis' design also. I do have one of his PCBs. His paper
lists the Eico 665 and 667 as vacuum tube testers that have been tested to
work. I found it odd that the 666 is *not* listed in his paper at all, even
in the "Should Work Just Fine" list.

I would be interested to know if anyone has successfully built the VTCT
using an Eico 666.

DaveD
KC0WJN


On Sat, Mar 15, 2025 at 09:01 ryanhart via groups.io <ryanhart=
[email protected]> wrote:

This is quite an old thread, and I'm unable to find the original, which is
even older.

I'd love to buy one of Dennis's boards. Is anyone selling them? I've read
his Oct. 2019, v1.04 paper on the tube tester-to-curve tracer adapter. It
sounds fascinating.

I have an Eico 666 that I think I could use for this. I have a Tek 577 on
the way that's described as being in perfect working order. It'll need a
once-over, but assuming the seller is an honest Joe, my hopes are high. I
certainly can use the 577 for other things as well, but matching tubes is
very high on my list of things I'd like to do with it.

Any info on where this project stands is much appreciated! Thanks in
advance for any info.

Ryan

Serials starting with a 1 are IIRC from the Guernsey plant

Here is a photo of the HV board showing the trimmer.

/g/TekScopes/photo/300558/3883505?p=Created%2C%2C%2C20%2C2%2C0%2C0

Regards,

Barry

Hi everyone.
I recently got a 2465B scope and replaced all leaky/high ESR CAPs.
The Dallas NVRAM was missing so I hacked in a FRAM and the machine did switch on; have to press A/B TRIG to proceed when the unit self tests (presumably TEST 04 FAIL).
The first thing is that, I had to adjust the GRID BIAS before I could see anything.
After adjusting, I noticed there're dots and weird characters on the screen.
I've read somewhere else that this has something to do with the CAL data.
So I tried to do the CAL procedures. But I cannot finish beyond the first step of CAL 08, the center dots dim with other dots as I adjust the GRID BIAS.
The Intensity trim pot seems to do nothing. Readout Intensity is either on or off.
The problem is very similar to this post on EEVBlog, and there's a video in this post:

Feeding in 10MHz sine wave into all 4 channels and they looks good except the flashing dots and weird characters.

Checked all voltages according to the 5-1 table, and traced down all lines related to the DI, ROI to the U650.
Before R361 and R353, dramatic changes on voltage when turning the pots. But checking the 22 and 23 pin of U650, changes were, however, in 100mV range.
Removing the U950 chip restore the amplitude to reasonable levels.
But this also did nothing the the screen. Everything is still in place - nothing disappeared, nothing changed - weird characters, dots, signals remain the same.

Test signals 22, 23, 65, 66 shown in the SM are way out on amplitude.
Feeding 3Hz 5Vpp signals into the Ext, Z-axis in did absolutely nothing to the screen.

I don't have another U950 on hand to test but the U950 seems to be the culprit?

This is quite an old thread, and I'm unable to find the original, which is even older.

I'd love to buy one of Dennis's boards. Is anyone selling them? I've read his Oct. 2019, v1.04 paper on the tube tester-to-curve tracer adapter. It sounds fascinating.

I have an Eico 666 that I think I could use for this. I have a Tek 577 on the way that's described as being in perfect working order. It'll need a once-over, but assuming the seller is an honest Joe, my hopes are high. I certainly can use the 577 for other things as well, but matching tubes is very high on my list of things I'd like to do with it.

Any info on where this project stands is much appreciated! Thanks in advance for any info.

Ryan

Jon,

The trimmer has “250R” markings and measures 250 ohm.

I have downloaded SC504 manuals from several sources. They are all the same version. I don’t know where else to look.

Thank you!

Barry

Thanks Tom, I looked having got caught by that one in the past, the connections look good. To be certain of a good connection I pulled the lugs off then popped them back on.

Andy.

If that first digit of the serial number is a 7, then it was assembled in Heerenveen. A six-number serial number without a letter and beginning with 7 indicates that it was assembled in Heerenveen, Netherlands.

Are you certain that the first character of the serial number is a 1?

I realize that it is more fun to build something from scraps and spares but have you considered finding an 1101 or 1101A lemo probe power supply?

Your serial number is odd.

All Tektronix scopes serial are form X0nnnnn

X-location of mfg, eg B Beaverton G Gurnsbery....
0 first digit is always 0
Second digit is the age, 1- oldest 5 most 6 latest

Thus a typical US number is B0503334

Jon

Reading further through service manual #1 section on 2ND LO tuning failure - there is an onboard calibration procedure (SHIFT 0 1 (calibration) 4 (2nd LO) - typo in the manual misses the 1 step). This provides prompts to adjust several tuning control potentiometers (4 or 5 total in sequence). In each step a measurement (made after a few seconds) was out of tolerance and prompt was offered as to which potentiometer to adjust. As I don't have the unit open, I just bypassed each of the steps. It appears that calibration of this type is manged through potentiometers rather than DAC outputs and the microcontroller, so the unit will be opened as soon as bench space is cleared for it.

I will update once I've completed (with success or failure) the calibration steps noted.

Wondering if anyonewho has a "spares" 465, 475, or 485 would be willing to pull a couple of the LEMO power jacks from the back (the four pin jackused to power Tek probes that use +/-15VDC) for me. I want to build a stand alone power supply so I can use some of my power-required probes on my 2465B, which aren't equipped with them.

email is K7WXWatqrpdxdotnet or message me here.

Thanks!
Bill

Re-ran the 2ND LO diagonstic at 100, 200, 500, 1000, 2000, 5000 and 10000 Hz/div span, the following was recorded

TUNING FAILURE - 2ND LO - VERY FREQUENT
Hz/div span TV Nominal DAC set 2ND LO Desired Counted
100 -0.04V -0.59V 2.181 993GHz 2.181 995GHz
Offset Desired Counted Off Set'g Acc'y
18.006 714MHz 18.004 660MHz 5Hz

TUNING FAILURE - 2ND LO - VERY FREQUENT
Hz/div span TV Nominal DAC set 2ND LO Desired Counted
200 0.08V -0.50V 2.182 008GHz 2.182 008GHz
Offset Desired Counted Off Set'g Acc'y
17.991 683MHz 17.991656MHz 5Hz

TUNING FAILURE - 2ND LO - INFREQUENT
Hz/div span TV Nominal DAC set 2ND LO Desired Counted
500 0.08V -0.50V 2.182 008GHz 2.182 009GHz
Offset Desired Counted Off Set'g Acc'y
17.991 683MHz 17.991 17MHz 12Hz

TUNING FAILURE - 2ND LO - NOT SEEN
Hz/div span TV Nominal DAC set 2ND LO Desired Counted
1000 0.08V -0.51V 2.182 008GHz 2.182 008GHz
Offset Desired Counted Off Set'g Acc'y
17.991 683MHz 17.991 68MHz 40Hz

TUNING FAILURE - 2ND LO - NOT SEEN
Hz/div span TV Nominal DAC set 2ND LO Desired Counted
2000 0.08V -0.51V 2.182 008GHz 2.182 009GHz
Offset Desired Counted Off Set'g Acc'y
17.991 683MHz 17.991 3MHz 80Hz

TUNING FAILURE - 2ND LO - NOT SEEN
Hz/div span TV Nominal DAC set 2ND LO Desired Counted
5000 0.08V -0.52V 2.182 008GHz 2.182 009GHz
Offset Desired Counted Off Set'g Acc'y
17.991 683MHz 17.991 4MHz 200Hz

TUNING FAILURE - 2ND LO - NOT SEEN
Hz/div span TV Nominal DAC set 2ND LO Desired Counted
10000 0.08V -0.52V 2.182 008GHz 2.182 009GHz
Offset Desired Counted Off Set'g Acc'y
17.991 683MHz 17.990 8MHz 320Hz

Suggest you get the exact service manual for the model and serial number of the scope

Most HV trim pots and control are megohms not 250 Ohm

Jon

I am looking for the VMT control software (and/or any other software) for the vintage 1996-1999 VM-700T NTSC/PAL video test set. Since this unit has been made "obsolete" by the sunset of the old analog TV transmission protocols, they are no longer supported by whomever took over the Tek video division. My unit has the audio option enabled, among others, and it would be nice to be able to more easily build some automated functions for it. Also are there any CLIP files available anywhere since this unit falls into the "board level exchange" era of servicing.

The test (previous post) was conducted at default power-up settings (1.8 GHz band, full span).

I'll repeat the test with narrow spans reflecting the sweep I wanted to run, and post the results.

Have had this 2755AP for 10+ years; for the first time in recollection I've needed to use very narrow span width (to inspect output of a HP synthesizer). Frequency being inspected is 1000 MHz. When span is set to 500 Hz/div, I get occasional "Tuning failure 2nd LO". When span is set to 200 Hz or 100 Hz/div, the error messages are more frequent but not continuous. The error message does not appear at power-up self-test.

I used Shift 0 3 to access "2ND LO DIAGNOSTIC AID".

Doesn't appear I can post the photo here, but this is the displayed info:

TUNE VOLTS NOMINAL=0.01V DAC SET = 0.19V
2ND LO FREQ DESIRED = 2.182.000GHZ COUNTED = 2.182.099GHZ
OFFSET FREQ DESIRED = 18.000 000MHZ COUNTED = 17.900MHZ
OFFSET SETTING ACCURACY 294.912KHZ

The verbiage in the service manual (volume 1, page 6-12, section titled "TUNING FAILURE - 2ND LO" includes the text

"The offset setting accuracy is the maximum permitted difference between the actual and desired offset frequencies. The setting process ends when the difference becomes less than or equal to this value. The tolerance depends on frequency span and band."

I'm puzzling over what this is trying to tell me.

Also I believe the analyzer has a built-in back-up battery which has not been touched in at least the 10 years I've had the unit here. Does the back-up battery store some calibration coefficients that could have been lost? There has been no error message related to back-up battery specifically.

Thanks!

Dave

Just a guess, but after some digging I suspect there is a different HV board layout/configuration for the 2 different CRT's available... anyone has any insight?

Regards,

Barry

I can't even tell what is the latest circuit configuration. Anyone have an idea?