Re: Recreating an old board for the 7854


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 Warner
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. The
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 testing.

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 caps 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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