Date   

Re: adjusting DAC REF voltage on 2465A

 

A difference of 9 mV on the 10 V supply won't influence calibration much if at all measurable, as you saw. Accuracy in these 'scopes is about 1 - 3 %.

Raymond


Re: 7A13 Vc readout options

Dave Wise
 

Topic is "Fun Tek IC listed (155-0185-00)". Announcement post by Steve Ditter - thanks, Steve!


Re: adjusting DAC REF voltage on 2465A

Amir Bozorgi
 

I just re-capped (several caps were failing) and replaced a resistor but did't adjust the PSU

Well, the 10V reference (pin 4 of J119) was reading 10.009 on my DMM. I changed it to 10.000 and back to 10.009
but could not detect any bit of difference whether in vertical or horizontal measurements (down to very small time or voltage differences) and I always check my measured results with 2 other digital scopes (a lecroy LC584AL and a siglent SDS1202X-E). So I went back to 10.000V.




thanks


Re: 7A13 Vc readout options

Dave Wise
 

There's already a Tek-made chip. Discussion should be in the archive. I can't check right now.

Dave Wise

On Nov 15, 2017, at 9:55 AM, Chuck Harris cfharris@erols.com<mailto:cfharris@erols.com> [TekScopes] <TekScopes@yahoogroups.com<mailto:TekScopes@yahoogroups.com>> wrote:

Today a little DVM is easy and tiny, but back then, it
was a mess of digital circuitry. The DVMs they made for
the TM500 frames aren't exactly empty shells.

Today I would take a 8 pin DIP/SOIC PIC12F629, and use one
of its 10 bid ADCs to measure the voltage, and send the
info out serially.


-Chuck Harris

edbreya@yahoo.com<mailto:edbreya@yahoo.com> [TekScopes] wrote:
While working on these 7A13s, I often wondered why Tek didn't just put the Vc comparison voltage display right on the CRT readout. There's a whole blank lower readout spot available, but they opted for first the mechanical readout, then later the LED version. I suppose it was maybe too complicated to fit back then, or perhaps to be compatible with non-readout-optioned mainframes.

All of my 7A13s have the LED readout, so no big deal for me, but there seems to have been a lot of lamenting the problems with the mechanical version, and the simple option of just reading the Vc monitor signal on a separate DVM.

If this is a large enough problem, I'd suggest that a cool modern solution is to build a DVM and RO interface circuit to measure the Vc and write it on-screen, where I believe it should have been all along. It seems that the control and signal processing should be trivial for you guys who whip up microcontrollers whenever needed, and the interfacing to the RO is quite simple.

The DVM function could be replicated using the same sort of comparison and counting circuits as in the LED version, but mostly replaced by the uC, or maybe using the built-in A/D functions of certain uCs. The RO interface basically needs simple 4-bit DAC functions to make the right row and column currents, and a little CMOS/diode logic to properly synchronize to the time slots. The DAC and synchronizing circuits can easily do the appropriate level shifting for the 15V RO signal environment, so 5V logic from the uC can control everything.

Just a thought.

Ed


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Posted by: Chuck Harris <cfharris@erols.com<mailto:cfharris@erols.com>>
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Yahoo Groups Links


Re: 500 series fan balancing

ae5i@...
 

In general, when balancing a fan like the ones in the 500 series scopes, also look at the pitch of each blade. The mass of the blade can be fine but if the pitch is significantly different from the others, it can cause vibration issues because the load is asymmetrical and the asymmetrical part of the load is being slung around in a circle!


Hope it goes well!


Tom


Re: adjusting DAC REF voltage on 2465A

 

Changing the PSU caps (which probably were not new during the most recent calibration) may have influenced your 'scope's calibration as well.
I hope you haven't adjusted the PSU after recapping because that would most likely have destroyed calibration.

Raymond


Re: adjusting DAC REF voltage on 2465A

 

adjusting geometry will be a problem
With geometry only slightly out of calibration as you state, I wouldn't mind about the slight influence. In general, it's less of a shift than what you cause by adjusting, i.e. if you straighten by moving part of the line half a minor division (left/right), loss of calibration will at most be the same amount at the same distance from image center.

Whether that's a problem in your situation is up to you to decide.

Raymond


Re: 7A13 Vc readout options

Chuck Harris
 

Today a little DVM is easy and tiny, but back then, it
was a mess of digital circuitry. The DVMs they made for
the TM500 frames aren't exactly empty shells.

Today I would take a 8 pin DIP/SOIC PIC12F629, and use one
of its 10 bid ADCs to measure the voltage, and send the
info out serially.


-Chuck Harris

edbreya@yahoo.com [TekScopes] wrote:

While working on these 7A13s, I often wondered why Tek didn't just put the Vc comparison voltage display right on the CRT readout. There's a whole blank lower readout spot available, but they opted for first the mechanical readout, then later the LED version. I suppose it was maybe too complicated to fit back then, or perhaps to be compatible with non-readout-optioned mainframes.

All of my 7A13s have the LED readout, so no big deal for me, but there seems to have been a lot of lamenting the problems with the mechanical version, and the simple option of just reading the Vc monitor signal on a separate DVM.

If this is a large enough problem, I'd suggest that a cool modern solution is to build a DVM and RO interface circuit to measure the Vc and write it on-screen, where I believe it should have been all along. It seems that the control and signal processing should be trivial for you guys who whip up microcontrollers whenever needed, and the interfacing to the RO is quite simple.

The DVM function could be replicated using the same sort of comparison and counting circuits as in the LED version, but mostly replaced by the uC, or maybe using the built-in A/D functions of certain uCs. The RO interface basically needs simple 4-bit DAC functions to make the right row and column currents, and a little CMOS/diode logic to properly synchronize to the time slots. The DAC and synchronizing circuits can easily do the appropriate level shifting for the 15V RO signal environment, so 5V logic from the uC can control everything.

Just a thought.

Ed


Re: adjusting DAC REF voltage on 2465A

Chuck Harris
 

adjusting geometry will be a problem as it changes the
relationship between the vertical/horizontal amplifiers
and the divisions on the screen. Its purpose is to warp
the deflection field so that the outer edges of the screen
are straight. In doing that, it affects everything else.

I wouldn't worry about it though, this scope is almost
certainly out of calibration.

-Chuck Harris

hewpatek@gmail.com [TekScopes] wrote:

Adjusting Geometry should not be a problem. Just placing the jumper in the CAL position is no problem but make sure you don't select or even do any of the "fly-by-wire" adjustments. The unsafe ones are the ones that are not done adjusting (capacitive) trimmers. BTW, you may do the geometry adjustment (R1870) without putting the 'scope into CAL mode by applying a signal and settings that will display appropriate vertical lines and adjusting R1870.

Raymond


7A13 Vc readout options

Ed Breya
 

While working on these 7A13s, I often wondered why Tek didn't just put the Vc comparison voltage display right on the CRT readout. There's a whole blank lower readout spot available, but they opted for first the mechanical readout, then later the LED version. I suppose it was maybe too complicated to fit back then, or perhaps to be compatible with non-readout-optioned mainframes.

All of my 7A13s have the LED readout, so no big deal for me, but there seems to have been a lot of lamenting the problems with the mechanical version, and the simple option of just reading the Vc monitor signal on a separate DVM.

If this is a large enough problem, I'd suggest that a cool modern solution is to build a DVM and RO interface circuit to measure the Vc and write it on-screen, where I believe it should have been all along. It seems that the control and signal processing should be trivial for you guys who whip up microcontrollers whenever needed, and the interfacing to the RO is quite simple.

The DVM function could be replicated using the same sort of comparison and counting circuits as in the LED version, but mostly replaced by the uC, or maybe using the built-in A/D functions of certain uCs. The RO interface basically needs simple 4-bit DAC functions to make the right row and column currents, and a little CMOS/diode logic to properly synchronize to the time slots. The DAC and synchronizing circuits can easily do the appropriate level shifting for the 15V RO signal environment, so 5V logic from the uC can control everything.

Just a thought.

Ed


Re: Leo Bodnar TD Pulser

David DiGiacomo
 

On Wed, Nov 15, 2017 at 12:57 AM, Sergey Kubushyn <ksi@koi8.net> wrote:
But for fast rise pulses HP 33002A is more than adequate. Please note that
130pS it generates is _NOT_ a rise time. It is _PULSE WIDTH_ that includes
both rising and falling edges and some sustained state inbetween so rise
time is something like 30-50pS.
Unfortunately, you can't measure or adjust a scope accurately with a
pulse that narrow. This can also be a problem with avalanche pulsers.


Re: adjusting DAC REF voltage on 2465A

 

Adjusting Geometry should not be a problem. Just placing the jumper in the CAL position is no problem but make sure you don't select or even do any of the "fly-by-wire" adjustments. The unsafe ones are the ones that are not done adjusting (capacitive) trimmers. BTW, you may do the geometry adjustment (R1870) without putting the 'scope into CAL mode by applying a signal and settings that will display appropriate vertical lines and adjusting R1870.

Raymond


Re: adjusting DAC REF voltage on 2465A

Amir Bozorgi
 

It's not only the edge focus, there is tiny bit of curvature on the delta_t cursors when I move them close to the left/right sides. So I plan to do to the CAL08 which needs the jumper to be positioned in CAL. Is that OK?


Thanks for valuable information on the DAC. I will not go after that then. The scope is working properly and perhaps needs a little bit of calibration (I am not even sure about that as I will explain in a separate post)
and I dont wanna end up with a scope that really needs calibration. I just brought it back to life after repairing the PSU and I am surprised that it is working near perfectly.


For now CAL08 would be enough.


thanks


regards


Re: adjusting DAC REF voltage on 2465A

 

CRT adjustments like trace rotation, (edge/high drive) focus and grid bias have no influence on calibration status. Still, since you mention only edge focus to be slightly off, I would just touch the relevant points. Grid bias isn't one of them, nor is trace rotation.

2.5 V as such is not the "ideal" value. The range should be enough and offset should be correct and both should be stable, since those are needed to allow the adjustments during calibration and stability of calibration afterwards. It's perfectly possible to have a 'scope in "perfect" calibration with slightly incorrect DAC voltages, as long as those were set before the other adjustments were made and have remained stable since.

You may check some calibration values by applying known DC voltages and (crystal) oscillator signals but don't be tempted to do just one or two of the "electronic" adjustments i.e. the ones that need the calibration jumper to be (re)moved because these 'scopes don't like being partially recalibrated and you may end up with a 'scope that tells you it needs calibrating!

Raymond


Re: 7a13 observations

Dave Wise
 

Thanks for your contributions, Ed. I will be following your work with interest.

Dave Wise

On Nov 15, 2017, at 8:25 AM, edbreya@yahoo.com<mailto:edbreya@yahoo.com> [TekScopes] <TekScopes@yahoogroups.com<mailto:TekScopes@yahoogroups.com>> wrote:

I'm wrapping up this 7A13 project for now, but wanted to offer some suggestions for those with busted mechanical readout type 7A13s. I will start a fresh thread for this.

Ed





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Posted by: edbreya@yahoo.com<mailto:edbreya@yahoo.com>
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Re: adjusting DAC REF voltage on 2465A

Amir Bozorgi
 

yes, maybe that pin is somehow disconnected although physically the J119 socket seems very fine and pretty much untouched in the past. I just found pin 17 of J511 on A5 thanks to your lead. This is connected to pin 13 of J119.
I will see if that pin can be probed when I go home tonight.


But now that you are saying adjusting the DAC ref will affect the calibration, I will not touch it as I dont have
the means to calibrate the scope. But I will try just to measure the DAC ref and see how close to 2.5 it is.




By the way, adjusting the CRT (CAL08) does not affect the calibration of the scope, does it?
because i need to do this adjustment and it seems pretty simple




thanks


regards


Re: 7854 adding more memory.

 

Hi Cliff,
Thanks for the update.
I would appreciate updates from Nathan on the progress of his replacement
RAM/ROM card.
Dennis Tillman W7PF

-----Original Message-----
Sent: Tuesday, November 14, 2017 9:35 PM
Subject: Re: [TekScopes] 7854 adding more memory.

The thread "7854 RAM card upgrade only - any interest?" is one I started
more than a year ago. The project does include the memory expansion by
default. The objective was to replace the old low density, high standby
current memory with low power RAM and a built-in lithium battery. This was
done by Tek starting with SN B100000, but these are quite rare. The older
7854s needed an external supply of 700 mA at about 6 V (ugh!) to make the
memory non-volatile, which makes it possible to retain programs and
waveforms when the scope is powered off. The project was expanded to combine
low power RAM and a ROM replacement on one card, as Tek did in the late
7854s. The ROM was added to replace failing Mostek ROMs in some scopes.
Tekscopes member Nathan Johnson has developed a prototype of this card and
it may become more widely available in the future. Expanding the RAM beyond
Tek's maximum of 8K was not pursued because of addressing and probable
firmware problems. There was an option (2D) from Tek to max (double to 8K)
the memory, but this became standard on all 7854s starting with SN B085121.


Regards, Cliff Carrie
________________________________
From: TekScopes@yahoogroups.com <TekScopes@yahoogroups.com> on behalf of
Dave Daniel kc0wjn@gmail.com Sent: Monday, November 13, 2017 3:45:09 PM
Subject: Re: [TekScopes] 7854 adding more memory.

IIRC, option 2D added an extra 4 kB to the 'scope.

Look in the archives for the thread entitled "7854 RAM card upgrade only
- any interest?" Starting March 4, 2016. There are over a hundred posts in
that thread on the subject of upgrading the memory in a 7854.

DaveD

On 11/13/2017 1:08 PM, 'Max Vaughan' maxvon@bendcable.com [TekScopes] wrote:
I believe this was discussed before, but I am finding thousands of
hits to wade through.
Some do not seem to be really relevant to the email subject.
Looking to add more memory to my 7854.
Older model, says version 04 on the service tag on the back.
I believe it only has the basic options.
Thanks in advance.
Max

KF7MAX


Re: 7a13 observations

Ed Breya
 

I'm wrapping up this 7A13 project for now, but wanted to offer some suggestions for those with busted mechanical readout type 7A13s. I will start a fresh thread for this.

Ed


Re: adjusting DAC REF voltage on 2465A

Amir Bozorgi
 

as I explained, the voltage on pin 13 of J119 is zero and everything with the scope works! I have checked it many times.


Re: adjusting DAC REF voltage on 2465A

 

Since you're writing that your 2465A operates correctly, incl. cursor movement etc., it seems a simple case of a broken connection to J119 pin 13. Since you need that pin only for calibration, you may probe the voltage anywhere in the 'scope.

Adjusting DAC voltage will influence calibration status.

On dwg 2, "Analog Control" (page 285 in your Service Manual) you'll find several places where you may probe the voltage.

Just be aware that the DAC is a current device, so probing voltages on the DAC IC itself (U2101) is not meaningful.

Raymond

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