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Help diagnosing a Tek 2755 spectrum analyzer

Neil Gruending
 

I'm out of ideas for trying to fix a Tek 2755 (2754/494AP) spectrum analyzer so I thought I would as the group for some ideas...

The symptoms are the all of the front panel LEDs are on and there's some random characters displayed on the CRT. It didn't always turn on so I recapped the AC power supply which fixed the turn on issue. I also found that the backup battery on the address card leaked all over the card making a real mess. I have cleaned and resoldered it a few times and it seems to work now, but I'm not 100% sure.

I have the service documentation for the 2754 and 494AP which describes how to initiate a self hardware test which is what I've been using to try and fix this thing. The self test mode sequence is:

1. Turn on DS1047 on the GPIB card
2. Verify the checksum for the ROM on the address card and turn off DS1047 if the sum passes.
3. Verify the instrument bus, writing "PROCESSOR SYSTEM TEST" on the CRT if it's ok or illuminating DS1050 if the test fails.
4. Continue remaining tests...

My 2755 is getting to step 3 and nothing visible happens, ie no words on the CRT and DS1050 is off. The fact that the ROM is passing the checksum suggests to me that my fixed address card is likely working. The processor is also able to control the LEDs because it's able to control DS1047 (they're on the same memory mapped latch) so it's unlikely DS1050 is faulty.

I'm assuming that something is wrong on the instrument bus so I tried pulling the cards one at a time to see if the fault went away but it didn't. Then I tried the instrument bus test mode while probing the bus but the waveforms do not match the service manual.

Any ideas on what to try next? Thanks,

Neil Gruending


Re: Wondering if there is any out there

Eric
 

The main unit serial number is B108698 the serial number of the 177 is B059769

On 2/14/2020 4:48 PM, Eric via Groups.Io wrote:
Michael,

Mine is defiantly the new style. The cap I am having trouble with is the user adjustable one on the front of the case. It does not have the 2 screws It has the panel mount nut. I will look up the serial number on the fixture when I get home but if memory serves it is a 50xxxx fixture.

Eric

On 2/14/2020 3:48 PM, Mlynch001 wrote:
   Looking at the schematic in my copy of the manual, I see that there is Text Box indicating "LOOPING COMPENSATION" with an arrow pointing above and to the right at C632.  C630 is a smaller trimmer cap used for the Looping calibration procedure Step 4 (Pg 5-6 + See Manual Change pages), it is located below and to the left of that test box in the schematic, not very clear on some scans of the manual. C630 is accessible through a hole in the bottom of the 177 fixture. Bothe C630 and C632 are mounted in the 177 Fixture, and C632 is definitely the operator adjustable front panel looping control cap.  C630 changed a couple of times through out production as well.  Looking at the Mechanical Parts list on my 177 Service Manual, it appears that only the first 215 units used the 4-40 screw mounted Looping Comp Cap.  After S/N B010316 they used a single nut and washer on the threaded neck of the compensation cap to secure it to the chassis.  Always good to have the serial number of your unit(s), especially with the 577/177 combination.  It is possible to mix early and late models of either component on this unit.  It is possible to have a very old 577 with a very new 177, or vice-versa.  This is something that I ran into on my units, since I obtained them from two different sources.


DS1742W-120 replacement adapter?

Tom B
 

Hello All,

Given that the Dallas DS1742W-120 is no longer available (excluding Chinese fakes), does anyone make an adapter board to use a more modern chip like the DS1744?

I noticed that Glitch Works makes a board for the DS1244.

See https://www.glitchwrks.com/2018/03/17/gw-1244-1


Tom Bryan
N3AJA


Re: New member and my story

Tim
 

Yep, I'm still around.
I'll be at rickreall tomorrow for the hamfest.
And I didn't forget that today is Valentine's day so my wife will be ok
with whatever I haul home tomorrow 😁

On Thu, Feb 13, 2020, 07:49 Randy Newman <randy.n.at.home@...> wrote:

Hi Tim:
Rickreall hamfest....wow.....I lived not far from there growing up. Now
live further north in Washington state. I happen to have 4 Tek scopes:
7834, 7633, 7623, and a fine 555 ( with 2 CAs, D, W, and 1A7). Plus various
other items from Fluke, HP, Keithley, Systron Donner, Analogic, etc.
Are you still involved in this forum?
Best wishes in Tek land.




Re: Wondering if there is any out there

Eric
 

Michael,

Mine is defiantly the new style. The cap I am having trouble with is the user adjustable one on the front of the case. It does not have the 2 screws It has the panel mount nut. I will look up the serial number on the fixture when I get home but if memory serves it is a 50xxxx fixture.

Eric

On 2/14/2020 3:48 PM, Mlynch001 wrote:
Looking at the schematic in my copy of the manual, I see that there is Text Box indicating "LOOPING COMPENSATION" with an arrow pointing above and to the right at C632. C630 is a smaller trimmer cap used for the Looping calibration procedure Step 4 (Pg 5-6 + See Manual Change pages), it is located below and to the left of that test box in the schematic, not very clear on some scans of the manual. C630 is accessible through a hole in the bottom of the 177 fixture. Bothe C630 and C632 are mounted in the 177 Fixture, and C632 is definitely the operator adjustable front panel looping control cap. C630 changed a couple of times through out production as well. Looking at the Mechanical Parts list on my 177 Service Manual, it appears that only the first 215 units used the 4-40 screw mounted Looping Comp Cap. After S/N B010316 they used a single nut and washer on the threaded neck of the compensation cap to secure it to the chassis. Always good to have the serial number of your unit(s), especially with the 577/177 combination. It is possible to mix early and late models of either component on this unit. It is possible to have a very old 577 with a very new 177, or vice-versa. This is something that I ran into on my units, since I obtained them from two different sources.


Re: Wondering if there is any out there

Mlynch001
 

Looking at the schematic in my copy of the manual, I see that there is Text Box indicating "LOOPING COMPENSATION" with an arrow pointing above and to the right at C632. C630 is a smaller trimmer cap used for the Looping calibration procedure Step 4 (Pg 5-6 + See Manual Change pages), it is located below and to the left of that test box in the schematic, not very clear on some scans of the manual. C630 is accessible through a hole in the bottom of the 177 fixture. Bothe C630 and C632 are mounted in the 177 Fixture, and C632 is definitely the operator adjustable front panel looping control cap. C630 changed a couple of times through out production as well. Looking at the Mechanical Parts list on my 177 Service Manual, it appears that only the first 215 units used the 4-40 screw mounted Looping Comp Cap. After S/N B010316 they used a single nut and washer on the threaded neck of the compensation cap to secure it to the chassis. Always good to have the serial number of your unit(s), especially with the 577/177 combination. It is possible to mix early and late models of either component on this unit. It is possible to have a very old 577 with a very new 177, or vice-versa. This is something that I ran into on my units, since I obtained them from two different sources.

--
Michael Lynch
Dardanelle, AR


Re: Wondering if there is any out there

Eric
 

Now I am honestly not sure. This is the looping cap that is actually in the test fixture 177 the curve tracer is a 577. From looking at the older documentation there are at least 2 versions of this. The early one needs a 3 hole mount the new one needs a one hole mount. I have the one hole version. The 577 has chips datacoded 91 so this is one of the very late model units.


Eric

On 2/14/2020 7:16 AM, Carl Hallberg via Groups.Io wrote:
Hi,
I'm not sure you have the right number.  Not 261.  The looping cap is C632 and number is 281-0197-01 made by E. F. Johnson.
Carl Hallberg (W9CJH)




On Thursday, February 13, 2020, 10:35:42 PM CST, Eric <ericsp@...> wrote:





I need Tek part number 261-0197-01 this is the variable high voltage loping Capacitor in a fixture 177. Or if anyone know of an equivalent replacement for it? It is C630 In the fixture




Re: 5116+5D10 intensity problem

Harvey White
 

Have you (and can you) safely measure the high voltage when this wandering happens?  First, though, I'd check ripple and voltage on the supplies.  That you have no stable trigger tends to make me think (in general terms) that there's ripple on the power supply somewhere.

It's possible that the supplies start good, and then something changes in the supply goes bad and the ripple goes up.

Harvey

On 2/14/2020 10:57 AM, Yeun-Jung Wu wrote:
I just digged out the A3 HV board and checked all the transistors, diodes except CR247, CR298, which is a 10kV, 5mA silicon diode and a 800V, 25mA silicon diode, respectively. I forgot to check the thick film hybrid resistor R272, which had multiple wire juction at A, B, C, D, E, F.

I also checked two aluminum electrolytic capacitors, 10uF/100V, and 10uF/50V. Their capacitance were 12uF with serial resistor about 2Ohms at 100Hz.

Putting everything back all the symptoms remain the same. I wondered if there was leakage of CR247 or CR298?

Now the horizontal and vertical expansion was about 1.5 graticules and varing slowly. Read out was still way outside the limit of screen. "Possible under-sampling" red LED warning lit all the time, stable trigger was not possible.



Re: 5116+5D10 intensity problem

Yeun-Jung Wu
 

I just digged out the A3 HV board and checked all the transistors, diodes except CR247, CR298, which is a 10kV, 5mA silicon diode and a 800V, 25mA silicon diode, respectively. I forgot to check the thick film hybrid resistor R272, which had multiple wire juction at A, B, C, D, E, F.

I also checked two aluminum electrolytic capacitors, 10uF/100V, and 10uF/50V. Their capacitance were 12uF with serial resistor about 2Ohms at 100Hz.

Putting everything back all the symptoms remain the same. I wondered if there was leakage of CR247 or CR298?

Now the horizontal and vertical expansion was about 1.5 graticules and varing slowly. Read out was still way outside the limit of screen. "Possible under-sampling" red LED warning lit all the time, stable trigger was not possible.


Re: 2465B Option 05 + 06 (TV/CTT)

@app41
 

Actually every panel owns all the necessary LEDs, you can even see them blinking through the panel at power on :)
The difference is that for the TV panel there is more labelling ("Line" trigger...), and there is transparency for theses 3 additional trigger LEDs.

So the TV option is still usable with standard panel, even if it would be nice to have the proper labels.

The wise solution would be to find the complete TV/CTT board (A26 671-0982-xx) and a used TV panel. I'm not in a hurry :)


Re: 2465B Option 05 + 06 (TV/CTT)

Siggi
 

IIRC there are also front panel differences that go with the TV trigger
option, there's an extra button and some labelling differences.

On Fri, Feb 14, 2020 at 8:16 AM Chuck Harris <cfharris@...> wrote:

Anyone who has that ASIC has, or at least had, the board
it was robbed from... I truly doubt there are any NOS
CTT ASICs anywhere in the world.

And, $250 buys you a couple weeks of lunches and Starbucks
at most... Just sayin' ...

-Chuck Harris

@app41 wrote:
Hello Chuck,

You're right, there is one ASIC but I can find it on ebay.
Actually the main problem is the crystal, its frequency is 13.10669MHz,
I can't find one.

I'd love to buy another 2465B but they are difficult to find in Europe,
and if I buy an oscilloscope from the USA I need to add about 250 USD for
shipping and tax...
That's why I'm looking for cheaper (and lighter !) boards :)


Guillaume



Re: 2465B Option 05 + 06 (TV/CTT)

Chuck Harris
 

Anyone who has that ASIC has, or at least had, the board
it was robbed from... I truly doubt there are any NOS
CTT ASICs anywhere in the world.

And, $250 buys you a couple weeks of lunches and Starbucks
at most... Just sayin' ...

-Chuck Harris

@app41 wrote:

Hello Chuck,

You're right, there is one ASIC but I can find it on ebay.
Actually the main problem is the crystal, its frequency is 13.10669MHz, I can't find one.

I'd love to buy another 2465B but they are difficult to find in Europe, and if I buy an oscilloscope from the USA I need to add about 250 USD for shipping and tax...
That's why I'm looking for cheaper (and lighter !) boards :)


Guillaume


Re: Wondering if there is any out there

Carl Hallberg
 

Hi,
I'm not sure you have the right number.  Not 261.  The looping cap is C632 and number is 281-0197-01 made by E. F. Johnson.
Carl Hallberg (W9CJH)

On Thursday, February 13, 2020, 10:35:42 PM CST, Eric <ericsp@...> wrote:





I need Tek part number 261-0197-01 this is the variable high voltage loping Capacitor in a fixture 177. Or if anyone know of an equivalent replacement for it? It is C630 In the fixture


Re: 5116+5D10 intensity problem

Yeun-Jung Wu
 

BTW I did not see neon, DS274, (DS271+DS272+DS273 in series) lit.


Re: 5116+5D10 intensity problem

Yeun-Jung Wu
 

Hello David:

Thank you for your prompt reply. I will wait overnight and try again tomorrow. It looked like e-beam was pushed twice as much in each direction. This could happen if electrons move slower, i.e. insufficient electron acceleration. Slower electron impact creates dimmer fluorescent light. It would all fit together as a reasonable explanation.

Best Regards,

Yeun-Jung Wu


Re: 5116+5D10 intensity problem

 

If you switch it off and allow it to cool down for (say) a few hours or overnight, does it work again for a while?

I'm thinking this might be one of the problematic epoxy potted HT transformers

David

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Yeun-Jung Wu
Sent: 14 February 2020 10:43
To: TekScopes@groups.io
Subject: [TekScopes] 5116+5D10 intensity problem

Hello:

:

After operation about one and a half hour the intensity gradually decay. It was accompanied by the expansion of horizontal and vertical graticutes. Now one dotted horizontal and vertical division expanded to include four real inner CRT divisions. Read out information was pushed outside of screen. Pushing the "Beam finder" button display a image filled out the entire screen (save + Power on), instead of a scaled down version of display. The intensity of the pattern was barely visible. Weak wave forms were still displayed on the screen; mostly with a red LED warning: possible under-sampling.


Re: 5116+5D10 intensity problem

Yeun-Jung Wu
 

BTW +-30V. 200V and 5V all were within spec. Haven't checked their ripple content yet.


5116+5D10 intensity problem

Yeun-Jung Wu
 

Hello:

Today I dig out my 5116+5D10 to display signal from FG501 and FG501A. I used "channal addition" to display added signal from two oscillators tuned to nearly 7kHz sine wave. At equal amplitude the expected envelope was beautifully displayed on the screen. Switch to X-Y mode display a dotted Lissajous pattern. Read out and cursor all function as expected.

After operation about one and a half hour the intensity gradually decay. It was accompanied by the expansion of horizontal and vertical graticutes. Now one dotted horizontal and vertical division expanded to include four real inner CRT divisions. Read out information was pushed outside of screen. Pushing the "Beam finder" button display a image filled out the entire screen (save + Power on), instead of a scaled down version of display. The intensity of the pattern was barely visible. Weak wave forms were still displayed on the screen; mostly with a red LED warning: possible under-sampling.

I had tried to adjust intensity range R245 on A3 board with little effect.

Should I go further to poke the wave forms at 21 and 26A/B? Was the problem in Z-axis amp or HV (pin 2 of CRT socket)?
Q222, Q234, Q226 all located in a hard to reached region so I had not checked their status yet.

Any suggestions? Thank you in advance.

Yeun-Jung Wu


Re: 2465B Option 05 + 06 (TV/CTT)

@app41
 

Hello Chuck,

You're right, there is one ASIC but I can find it on ebay.
Actually the main problem is the crystal, its frequency is 13.10669MHz, I can't find one.

I'd love to buy another 2465B but they are difficult to find in Europe, and if I buy an oscilloscope from the USA I need to add about 250 USD for shipping and tax...
That's why I'm looking for cheaper (and lighter !) boards :)


Guillaume


Wondering if there is any out there

Eric
 

I need Tek part number 261-0197-01 this is the variable high voltage loping Capacitor in a fixture 177. Or if anyone know of an equivalent replacement for it? It is C630 In the fixture