Re: Recreating an old board for the 7854


I got the fix in. Kicad is weird if anything moves you need to hide and reapply the ground planes to get them to reconnect. Also the footprints of some of the IC's power and grounds nets are not baked in to the foot prints so I have to set them manually. The ground planes simplified some things and moving some parts around was able to get the layout complete. I am currently up to REV6.

Thanks again for all the input.

-----Original Message-----
From: <> On Behalf Of Andy Warner
Sent: Monday, September 20, 2021 9:09 AM
Subject: Re: [TekScopes] Recreating an old board for the 7854

Vias are free and reliable for signals at the speeds of this board. Use them, is my advice.

Also, I suspect there is a systemic problem with the connectivity to the ground pour, I used U520 as an example, as best I can tell the same applies to the power grounds of other chips too. I would look for the systemic fix rather thank the kludge (but I'm not the one who has to spend the time finding that systemic fix.)

On Mon, Sep 20, 2021, 07:53 <Zentronics42@...> wrote:

I got the u520 pad to connect. It did not line the tract
running from the bypass cap over to the pin for some reason it is all
ground but it did not want to connect to the ground plane. I am going
to go with weird software quirk. In terms of the routing between smd
parts. I will see what I can do to sharpen the pencil come more. Those
3 traces are continuing to cause me some issues. But I will see what I
come up with. Part of this is I am being stubborn and not wanting to break down and use a via or 2.
Currently the layout doesn’t have any so I am trying to keep it that way.
Might be a bit unrealistic but I am getting closer.


-----Original Message-----
From: <> On Behalf Of Andy
Sent: Monday, September 20, 2021 1:34 AM
Subject: Re: [TekScopes] Recreating an old board for the 7854

Something is not right with the ground pour in the rev 4 drawing you
uploaded. For instance pin 7 of U520 only connects to the ground plane
indirectly. I am not a kicad user, so I cannot begin to suggest a root
cause or remedy, I am afraid.

You are also back to routing between SMT pads with rev 4 (I just
realized that I replied to the file upload message, so you might not
have seen it, repeating here in case you missed it.)

On Sun, Sep 19, 2021 at 22:59 <Zentronics42@...> wrote:

I used a mix for a few reasons. I wanted to keep to a 2 layer board
to keep the cost down. The THT resisters and pins solved some unique
challenges to the layout. I was able to pull the board off with zero
vias. Also this needs to be a double sided board due to the card
edge connectors. An additional point is some of the connections on
to the scope are on the back of the board. The pull up resisters one
the logic lines helped with routing check out the difference between
rev 1 and rev 2 of the PCB's especially in the digital section. The
first run out routing was awful, and I am saying that as the one
that created it. In the triggering section which is the only high
speed signals on the board I stayed with SMD parts to keep the
inductance down and help with the edges The transistors I have pick
can run about
800 Mhz. Not crazy fast but not TTL slow either. These need to be
better than
400 Mhz as that is what the frame is. The card is used to do a
thermal compensation of the vertical amps in the scope when it is up and running.
Everything else on the board is just termination and test points.
2 critical places are the IC's and the pre trigger section. Also due
to needing Tek connections to make the board work it will have to be
hand assembled in the lab I cant get a place to fab it for me. At
least not fully.

I have uploaded what I hope will be a final layout for a new version
of the
67-0912-00 This board has the decoupling caps in place for the IC's
as well as the ground planes and all the test points. I will be
working on a shopping list (BOM) for the parts needed. Then boards
spun and

A huge thanks to Andy, Ke-Fong lin, and Holger for helping me get
this project off the ground and on to a PCB. Your assistance and
input is greatly appreciated and immeasurably helpful in getting the
layout to this point.

As part of my repair and calibration of my 7854 I do have 2
questions . I have a 7854 that has been damaged in shipping the
digital section is very compressed, but I have ruled out the tube
and analog parts of the scope as they display correctly. It is just
the stored wave form and the readout that is weird. I am curious if
any one has seen this before and knows where to look.
Also is there information about upgrading the firmware for the 7854?
My working one is a low serial number 41838 so I know it will suffer
from rom rot sooner or later so I would like to run the best
firmware on some newer chips. I am not sure if it matters but both
units are 2D so they have the expanded memory option.

-----Original Message-----
From: <> On Behalf Of Nico
Sent: Friday, September 17, 2021 10:49 AM
Subject: Re: [TekScopes] Recreating an old board for the 7854

Maybe a silly question that has already been asked before, why did
you use through-hole components and not SMD ? OK, I admit, area is
not an issue here.

From: <> on behalf of
Zentronics42@... <Zentronics42@...>
Sent: Friday, September 17, 2021 15:50
To: <>
Subject: Re: [TekScopes] Recreating an old board for the 7854

That was the plan. If the digital section looked good I am
going to add the decoupling caps and then do a ground pour. Then it
will be off to fab. I am even adding a bit more decoupling then what
was originally called for in the schematic. With a few 47uf bulk
for the board.


-----Original Message-----
From: <> On Behalf Of Andy
Sent: Friday, September 17, 2021 12:59 AM
Subject: Re: [TekScopes] Recreating an old board for the 7854

I did not notice it before, and it apparently was missing from the
original design, but I would consider adding more decoupling caps
close to the logic chips. Plenty of 0.1uF caps sprinkled around is
cheap insurance against glitches.

Apart from that, the layout does look better.

On Wed, Sep 15, 2021 at 20:58 <Zentronics42@...> wrote:

I have uploaded iteration 3 of the test card. I do need to pour
the fill zones on the board but changing the resister to THT parts
helped with the routing immensely. I also bumped up the thickness
of the traces and I also took care with the 90 degree corners. If
the board looks good and there is no gross mistakes I will clean
up the silk screen, get a few boards spun, and move on to testing.



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