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Hi Everybody,

This one is for 7000 series readout experts, hope you're out there
somewhere. I have a properly working late model 7854 that I'd like to use
with my 7L5 (early serial with old digital board, successfully converted
for use in 7854, will post full instructions on this modification later as
officially these do not exist for the old 7L5). Everything works fine
except the damn level readout that I really, really need because I heavily
use the 7854 averaging and math functions. The problem can be split in two
points:
1. Incorrect level readout in LIN mode - turning the attenuator should
produce the expected 200mV-100mV-50mV-20mV... sequence, but instead 7854
displays 2mV-1mV-5mV-2mV... and so on in circle (zeroes are omitted, units
and first digit are fine).
2. 7L5 readout driving circuitry can be slightly modified to fix the
mentioned problem, but although that fixes the display perfectly (and is
fully compatible with other mainframes using "classic" readout boards), it
breaks the ability of the 7854 storage to correctly obtain a scale factor
for acquired waveforms. So to summarize:
- If readout is broken in 2mV-1mV-5mV-2mV... way, 7854 acquire command (at
least) captures the same scale factor (2mV-1mV-5mV-2mV...)
- If readout is fixed to show 200mV-100mV-50mV-20mV..., 7854 acquire
command displays a warning and sets 1 as the default scale factor

I believe the problem is fully on the 7854 side, now for some gritty
technical details if you're still with me. 7L5 uses a non-standard (but
still technically perfectly correct) mode to display readout, using all 10
time slots (TS1-TS10). For example the word "200mV" in LIN mode would be
encoded in the following way:
ROW address: 3221115545
COL address: 0003110012
where digit position denotes a time slot (from left to right TS1-TS10). For
comparison word "-123dBV" in LOG mode would be:
ROW address: 2221115545
COL address: 0062346702
Quick reference to the address table:

Column address 0 in TS1 denotes a SKIP operation, it's obvious that the two
zeroes in 200mV are coded in TS5 and TS6 (non-standard format) as opposed
to standard format that uses TS1 to specify "add one zero" or "add two
zeroes" operational addresses. So if 7L5 does a SKIP in TS1, ROW address
should make no difference (as long as it's in 1-9 range). On mainframes
with classic readout boards (tested on 7633 and 7104) it indeed makes no
difference, but on 7854 it painfully breaks stuff:
- if ROW=2 in TS1, readout correctly displays 200mV-100mV-50mV-20mV... but
storage acquire fails to obtain the scale factor
- if ROW=3 in TS1 (7L5 factory default), readout breaks and displays
2mV-1mV-5mV-2mV... storage acquires the (broken) scale factor
- if ROW=4,5..9 in TS1, readout correctly displays 200mV-100mV-50mV-20mV...
but storage acquire fails to obtain the scale factor
7000/7854 readout specification makes no mention of such nonsense. To add
to the confusion, 7L5 service manual mentions Q2325 (page 2-19) that sets
ROW=3 in TS1 in LIN mode (although TS1 COL=0 which denotes SKIP), but with
no explanation. In LOG mode Q2325 is off and ROW=2.

I wonder if all 7L5s (including ones with new digital boards) suffer from
this problem in 7854. I already lost weeks trying to fix this and I'm quite
disappointed. Conversion to make 7854 capture 7L5 spectrums was piece of
cake, but this "tiny" readout bug is a nightmare if you make a lot of
average level measurements.

If anybody has any hints or extra documentation on 7854 readout, I'd
appreciate any help...

Best Regards,
Nenad Filipovic

On Mon, Jul 2, 2018 at 01:03 pm, Nenad Filipovic wrote:

I wonder if all 7L5s (including ones with new digital boards) suffer from
this problem in 7854. I already lost weeks trying to fix this and I'm quite
disappointed. Conversion to make 7854 capture 7L5 spectrums was piece of
cake, but this "tiny" readout bug is a nightmare if you make a lot of
average level measurements.

If anybody has any hints or extra documentation on 7854 readout, I'd
appreciate any help...

This problem was addressed In a WW (Wizards Workshop) article from 2-85 which
said it was fixed by Mod 50646. It is only a change of one resistor value in the 7L5:
Change R2340 on the Vertical Board (A200A2) from 150k to 49.9k.
/H?kan

H?kan,

Do you have scans of the Wizards Workshop articles. They sound like an incredibly useful reference.

Dave

From: [email protected] [mailto:[email protected]] On Behalf Of
zenith5106

This problem was addressed In a WW (Wizards Workshop) article from 2-85

which

said it was fixed by Mod 50646. It is only a change of one resistor value

in the 7L5:

Change R2340 on the Vertical Board (A200A2) from 150k to 49.9k.
/H?kan

Hi H?kan,

Thanks for your response, I already tried all reasonable values of R2340.
In effect this means that I tested all TS1 ROW addresses from 2 to 9 (the
suggested value of 49.9k equals ROW=5). And although readout display
becomes perfectly correct for ROW values of 2, 4, 5, 6, 7, 8 and 9, in all
of these cases the 7854 Acquire command fails to obtain/set the scale
factor.

I'm sure this problem is fully on the 7854 side. Do by any chance these WW
articles have any info on 7854 readout mods? Any hint where I could
find/download them?

Best Regards,
Nenad Filipovic


On Tue, Jul 3, 2018 at 1:21 AM, David C. Partridge <
david.partridge@...> wrote:

H?kan,

Do you have scans of the Wizards Workshop articles. They sound like an
incredibly useful reference.

Dave
-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of
zenith5106
Sent: 02 July 2018 23:02
To: [email protected]
Subject: Re: [TekScopes] 7854 readout does not conform to specification?
(7L5 problem)

This problem was addressed In a WW (Wizards Workshop) article from 2-85

which

said it was fixed by Mod 50646. It is only a change of one resistor value

in the 7L5:

Change R2340 on the Vertical Board (A200A2) from 150k to 49.9k.
/H?kan

On Mon, Jul 2, 2018 at 04:21 pm, David C. Partridge wrote:

H?kan,

Do you have scans of the Wizards Workshop articles. They sound like an
incredibly useful reference.

Wizards Workshop was an internal Service magazine distributed to all Field Offices.
It contained service tips and mod info on pretty much any supported Tek product.
I don't recall how often it came, possibly on a monthly basis. Articles for each instrument
were then saved together on microfiche and added to the collection of the instrument.

So the answer to your question is no but I have pretty much all on microfiche.

Nedad, I'l check on 7854 tomorrow.
/H?kan

I'm sure this problem is fully on the 7854 side. Do by any chance these WW
articles have any info on 7854 readout mods? Any hint where I could
find/download them?

Best Regards,
Nenad Filipovic

The same article (as 7L5) was also in the 7854 archive. There were no other specifically for this problem
There was another about readout issues which may, or more likely, may not fix your problem.
You can find it here:

/H?kan

On Wed, Jul 4, 2018 at 1:20 PM, zenith5106 <hahi@...> wrote:

The same article (as 7L5) was also in the 7854 archive. There were no

other specifically for this problem

There was another about readout issues which may, or more likely, may not

fix your problem.

You can find it here:

/H?kan

I just checked and my 7854 already has this mod, so I'm out of luck. Thanks
for sharing the mod anyway.
I suppose this problem is in the firmware (ROM), since it's the CPU that
decodes the readout and sets the scale factor. Unless there's documentation
or anybody familiar with 7854 ROM content, I doubt there's anything that
can be done about it.

Best Regards,
Nenad Filipovic