Hello Gerrit,

Thanks for answering? The "image" is aligned to the scope, and the DOT movess with the alignement.
I understand? the manual, that the DOT is the point, where he named dot frequency is set. That means, that with a display of 000 kHz, the
DOT should be in the same horizontal place as the DC Marker ?!
The 600 Hz offset is present a the 000 kHz as well as with the 500 kHz ( Reference ). The calibrator signal counted shows with a trustable counter about 500,006 kHz.
But it is shown with the same 600 Hz offset ( to the right of the DOT.
By this, I thik, that the internal TCXO of 10MHz should be relative fine !?
What is interesting is, that the offset is nNOT a multiple of the fine displacement of 250 Hz. This means, the the PLL as no "step error" !
The offset is the same with and without digital storage.
Up to now, I did not find any clou who is definiing the position of the DOT in? relation to the frquency saw tooth of the horizontal display ?!
The schematics and the design is for me not very starte forward.

Herbert

Both HOR and VER POS need to be adjusted to mate plugin to the scope.

Suggest use HOR POS control to calibrate the 7L5 to the scope.


Set zero DC peak at left scale line

Jon

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Hi,
Many thanks to all who responded to my post. My mistake, It is a 7B92A ... I missed the 'A' out. Looks like I have resolved the issue. I think it was just a connectivity problem. With the side mainframe side panel removed I left it running this morning, and as expected, it stopped sweeping after about 30 mins. Armed with the knowledge that there are a lot of socketed devices in there, I took a plastic trim-tool and prodded the board. Bingo! the trigger light came back on and it hasn't failed since. If only all faults were that easy!!

I think it was just the Main Sweep that was affected also.

Thanks also for the info regarding the incompatibility issue ... I have replaced the 7B92A with a 7B53A.

Thanks again,

Ian, GM0UHC

Hi.

It might be a calibration issue, between 7L5 and mainframe, or within the 7L5 itself.

What does it look like if you turn off the digital storage?? If there is horizontal or vertical discrepancy between non-store, and with storage on, it needs some adjustment.

Do, read the circuit description first though.? Especially how it accomplishes the tuning and just what the "Dot Marker" relates to.

If you have the manual, try the performance check's and the calibration procedure, but NOT adjusting anything, yet.? You'll need two plug-in extenders of course.

The manual (if you've not got a paper version) can be had from :-


But check it is relevant for the serial number of the instrument you have.

Working on those is "interesting" to say the least.? It's very compact inside, and very easy to damage things if you slip while probing or adjusting something.? In the unlikely event you need to change any component, especially on any of the digital storage/averaging subsystem, be aware, that some of the digital PCB's are (from memory) up to 10 layer types!? (Hold up to the light, and you'll see layer markers in one corner, or along one side.)? And are all too easily damaged.

I used to work at Tek in the UK back then, and lost count of the number of those boards I had to change after a third party attempted to replace a chip.? Sometimes, a repair can be made, but if a via was pulled out with a component leg, and it was connected to more than one layer inside the board, that's likely a write off, unless you like a lot of detective and very fine wire work...

Very nice instruments when working though, if a bit fragile for some users.

Dave B.
Ex Tek UK, when the 7L5 and similar were still new and supported products.

--
Sent from a MicroSoft free zone:

Hello out there,
I am a little bit used to work with SA and I know, that almost every SA ( if not supressed by the display system ) shows a DC-Peak, which means the system is receiving his own LO.
This peak should, as I understand the 7l5, be congruent with the "Dot Marker" on the screen when the Dot Frequency is set to ZERO.
My 7l5 shows this DC- Peak arround 600 Hz above the Dot Marker whne running without input signal.
When I apply a 1KHz signal, this DC Peak is joined by two more peaks, one 1KHz above the DC Peak and one 1kHz below the DC Peak ( Mirror of the normal displa.
So, what went wrong ? The display content is always shown arround 600 Hz to high.

Has anyone an idea what I am awaiting wrong, or how this can be fixed ?

Best regards

Herbert / DD0PC/CT2IJD

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If I remember correctly, the 7B92 uses a tunnel diode for a trigger generator.? I'd take the trigger signal and trace it through.? I'd look to see if the tunnel diode fails to generate a trigger, and if so, I think there's a bias adjustment for the tunnel diode.? It's possible that the pot for the adjustment is failing.? There is a mode, I think, where the tunnel diode is not used, HF sync comes to mind.? Does that work?

There's also the possibility that the trigger amplifier is somehow giving up, or drifting.? I assume that the voltages are correct?

Could this be a thermal problem?

I have 7B92A, not 7B92.

These are guesses, and I may be mixing up the A and non-A.

Harvey

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Hi,
I'm new to this group. I have a 7603 Mainframe and the following plug-ins:-

2 x 7A26, 7A11, 7A19, 7A22, 7D13, 7B53A, 7B80, 7B85 and 7B92.

Unfortunately, the 7B92 has developed a trigger fault where after about 30 minutes, the timebase fails to trigger.
Any suggestions would be greatly received before I go digging.

I don't have an extender, so know this might be a tricky fault to chase.

Many thanks in advance,

Ian, GM0UHC

The front panel should be very similar to the 500 series scopes, so the schematic that's available should get you started.

No schematics for the 600 or 700 series was ever released though unfortunately. We keep wishing upon a star that Tek releases it (completely unlikely) or someone leaks it (about the same chance..)



Jared

Thanks, Jon.

Happy New Year

Mike, the very old tube 1A plugins for 1960s 500 series Tek are not a good solution.

Never seen 1A plugins power without a 500 scope.

Depending on your signal source, and BW, RT, noise, and dynamic range,requirements, I can offer better ideas.

The differential probes are either very costly, prone to blowout from over voltage, or junk from China.

? simple solution is a differential amp IC and a DIY box, switch.

See app notes of Linear Technology, National Semiconductor, and Tektronix Circuits Concept book Oscilloscope Probe Circuits

Bon courage

Jon

Hi Jon,
? I was hoping to have a newer version of the old 1A1 preamplifier that has an switchable output for A, B, and A-B. ?I can get an old 1A1 but the power supplies, such as the 127, are very hard to get. ?There was an updated pre-amp, I think 1A7A but again you need the power supply.

? I think I can use a differential probe to do the same measurements so I am looking at taking that path. ?

Regards,
?Mike?

Mike, just checked one of my Tek 2465B, indeed Ch 2 Out is exactly CH2 and is not affected by the invert or CH1 add CH2 buttons.

Only the on screen display is affected by invert or add.

A difference amplifier IS already a subtraction of input 1 - input 2 or input plus - input -.

Your question is unclear as to ref to2465 or plugin of scope or AM 502 etc

Jon

Thanks,

? I wonder if I could extract the A-B output from one of the plug-in difference amplifiers. ?I would like to have the A, B, A-B voltages to send to my wave analyzer.

mike

Bonjour, bravo for the good question.

Depending on he signal levles, desired CMRR and BW, may options are avaialble for a diff amp, CH1-CH2.



But The external VERT output of all 2465/7x TEK are CH 2 SIG OUT and a side chan of the CH2 amp.
CH1-CH2 is derived in the Ch mux hybrid and is NOT sent to the CH 2 SIG out.
Main use of CH 2 SIG is to monitor on ext device eg counter, or to strap to CH 1 in for additional gain.
Even if you obtained an ext CH1-CH2, the accuracy and CMRR will give some error, perhaps 2..5%.

See TEK service and op manual for your model and SN.

We use TEK 7000 MF and plugins designed for diff ue eg 7A22. Also suggest TM500 plugin AM502, excellent diff amps with BW limit controls.
Finally external diff amps are useable, such as our old friend Greg LEYH instruments #29 amp, x1/10/100/500 full diff. see lod.org.

Bon Chance

Jon

I have a 2465A and hoping I can get an output for Ch. 1 - Ch2, much like the old 1A1 preamplifier. If I invert ch.2 and add to ch.1 will the output on the back bnc (ch. 2 output)
give me the ch1 - ch2.? ?

Is there any more modern preamp than the 1A1 that has that function?

Regards,
mike zias / W3JRR

Just found my 7CT1 plugin curve tracer. Used In a large CRT MF like 7603 its great.

Needs a vert PI in the H slot or H PI with X (ext) input.

Only 50V but small and handy compared to the giant 576, 577 and 500 tube tracers.


Finally the TEK test fixtures are rare but very handy, only diff the 577/576 test adapters is they are 5 terminal Kelvin, but still can work on the 7CT1.

Jon


PS: 7CT1 have a pair of axial lytics C30, C32 100 uF that were 25V rated on 30V bus.

A TEK mod later replaced them with 100 uF 50..100V.