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On Fri, 16 Jul 2021, Sergey Kubushyn wrote:

On Thu, 15 Jul 2021, John Miles wrote:

I'm almost 100% sure it is just a snafu that happens all the time and was
quite widespread back then when CAD didn't exist yet but leave 0.00001%
doubt of missing something.

Agreed, that is very weird. Same with those resistors... usually you try
to
minimize the number of BOM line items by consolidating resistors, but they
seem to have done the opposite here.

The LC BPF at the output of the A69 post-VR amp is also funky. On the
schematic, the inductors are 0.652 uH, 0.568 uH, 0.652 uH, 0.94 uH, 1.047
uH, 1.047 uH, and 0.94 uH, but in the parts list they are more
reasonable-looking values. Meanwhile, the capacitors are bog-standard 220
pF and 470 pF parts.

The filter could be explained by the engineering department getting a
little
too carried away with their new computer, or maybe they just measured the
parts they used and transcribed the values to the BOM without rounding.
Likely true for the "1.047 uH" toroids, but it doesn't explain the others,
and nothing explains CR3068 as far as I can tell. I wonder if it's an IP
protection feature. If Hickok or Lavoie or somebody like that were to
clone
the instrument, things would get awkward if they had to explain what that
diode was for in court. Similar to the practice of adding fictitious
towns
to a map to guard against commercial copying.

I doubt that IP protection guess. Back then they didn't have CADs and those
designs were not just computer files. It was a bunch of paper drawings,
mylar tape PCB designs and so on. Not even starting on somebody willing to
make verbatim copies, it was totally impossible even if somebody decided to
do that. There was no way to just COPY something back then. Yes, one could
take the Tektronix schematics (that were not secret and were included in
service manuals) and make a copy of their instrument. You still had to go
through entire cycle of at least re-drawing their schematics, then do
mechanical design, PCB layout (with Mylar tape or something like that) and
much more. There is no way one could do this using just dumb monkeys -- it
would require engineers. And such things like that diode or multiplying BOM
lines is almost impossible to miss -- it would've been noticed and fixed in
the process. That is not even starting on their proprietary chips and other
stuff that should've been somehow re-implemented.

It is not like you can just blindly copy [stolen] design files and do
something with your own label as it is possible today. It was way more labor
intensive back then and it required brains. Brains were an absolute
necessity back then. It is a handicap nowadays but back then things were
totally different...

BTW, I forgot to mention that actual board matches schematic exactly. Don't
know about those inductance values -- have absolutely no interest
desoldering and measuring those -- but actual parts are ALL there. There is
a CR3068 (something like 1N4148) right next to 'LS145 pins, that 2.2K
resistor in ONE place instead of 3.3K everywhere is actually a 2.2K one and
the rest is actually 3.3K and so on...

---
*
* KSI@home KOI8 Net < > The impossible we do immediately. *
* Las Vegas NV, USA < > Miracles require 24-hour notice. *
*

On Thu, 15 Jul 2021, John Miles wrote:

I'm almost 100% sure it is just a snafu that happens all the time and was
quite widespread back then when CAD didn't exist yet but leave 0.00001%
doubt of missing something.

Agreed, that is very weird. Same with those resistors... usually you try to
minimize the number of BOM line items by consolidating resistors, but they
seem to have done the opposite here.

The LC BPF at the output of the A69 post-VR amp is also funky. On the
schematic, the inductors are 0.652 uH, 0.568 uH, 0.652 uH, 0.94 uH, 1.047
uH, 1.047 uH, and 0.94 uH, but in the parts list they are more
reasonable-looking values. Meanwhile, the capacitors are bog-standard 220
pF and 470 pF parts.

The filter could be explained by the engineering department getting a little
too carried away with their new computer, or maybe they just measured the
parts they used and transcribed the values to the BOM without rounding.
Likely true for the "1.047 uH" toroids, but it doesn't explain the others,
and nothing explains CR3068 as far as I can tell. I wonder if it's an IP
protection feature. If Hickok or Lavoie or somebody like that were to clone
the instrument, things would get awkward if they had to explain what that
diode was for in court. Similar to the practice of adding fictitious towns
to a map to guard against commercial copying.

I doubt that IP protection guess. Back then they didn't have CADs and those
designs were not just computer files. It was a bunch of paper drawings,
mylar tape PCB designs and so on. Not even starting on somebody willing to
make verbatim copies, it was totally impossible even if somebody decided to
do that. There was no way to just COPY something back then. Yes, one could
take the Tektronix schematics (that were not secret and were included in
service manuals) and make a copy of their instrument. You still had to go
through entire cycle of at least re-drawing their schematics, then do
mechanical design, PCB layout (with Mylar tape or something like that) and
much more. There is no way one could do this using just dumb monkeys -- it
would require engineers. And such things like that diode or multiplying BOM
lines is almost impossible to miss -- it would've been noticed and fixed in
the process. That is not even starting on their proprietary chips and other
stuff that should've been somehow re-implemented.

It is not like you can just blindly copy [stolen] design files and do
something with your own label as it is possible today. It was way more labor
intensive back then and it required brains. Brains were an absolute
necessity back then. It is a handicap nowadays but back then things were
totally different...

---
*
* KSI@home KOI8 Net < > The impossible we do immediately. *
* Las Vegas NV, USA < > Miracles require 24-hour notice. *
*

Or the famous Cadence vs. Avanti EDA code lawsuit.? Very hard for Avanti to explain the exact same misspellings in the comments!? Sure you didn't steal Cadence's IP, Avanti!? Case closed.? ? ? ? ? Jim Ford?Sent from my Verizon, Samsung Galaxy smartphone

On Thu, 15 Jul 2021, Ed Breya via groups.io wrote:

Eh, there is NO logic needed. Wired OR is done without any diodes using
OC/OD outputs. And it is done like that at the very bottom of the schematic.
On the same 'LS145, just different 2 outputs.

There is no different biasing -- 2N2907 emitter is connected to +15V, 10K
from emitter to base, 10K to 'LS145 OPEN COLLECTOR output. When that output
is high, 2N2907 base is connected to its emitter and that 10K to 'LS145 OPEN
COLLECTOR output is just hanging in the air. Transistor is closed, no
collector current. When 'LS145 output is active (low), that 10K is grounded
and there is base current that makes transistor open fully, to saturation.
2N2907A has beta at least a hundred, so that base current is more than
sufficient for full saturation. Emitter is at +15V wrt ground so a diode
drop makes no difference.

The schematic is classical RF diode switch. No level shifting with diodes.
No special biasing -- it is either ~+15V or ~-15V. Plus/minus couple of
volts makes absolutely no difference.

Please, don't play a guessing game with trivial advices. Just look at the
schematic.

I'm 99.9999999% sure it is just a snafu caused by multiple people and even
departments working on that schematic before it reached manufacturing. There
is no sacred knowledge or black magic there, the thing is trivial.

If it is purely a (TTL) logic section, it could be that a little
diode-logic was added to save a gate package or such, and required a
little different biasing to assure proper levels. Often, a Ge or Schottky
diode could be used with a saturated transistor output to get a valid
TTL-low when isolation is needed, or a regular Si diode could work with
some biasing help.

---
*
* KSI@home KOI8 Net < > The impossible we do immediately. *
* Las Vegas NV, USA < > Miracles require 24-hour notice. *
*

I'm almost 100% sure it is just a snafu that happens all the time and was
quite widespread back then when CAD didn't exist yet but leave 0.00001%
doubt of missing something.

Agreed, that is very weird. Same with those resistors... usually you try to
minimize the number of BOM line items by consolidating resistors, but they
seem to have done the opposite here.

The LC BPF at the output of the A69 post-VR amp is also funky. On the
schematic, the inductors are 0.652 uH, 0.568 uH, 0.652 uH, 0.94 uH, 1.047
uH, 1.047 uH, and 0.94 uH, but in the parts list they are more
reasonable-looking values. Meanwhile, the capacitors are bog-standard 220
pF and 470 pF parts.

The filter could be explained by the engineering department getting a little
too carried away with their new computer, or maybe they just measured the
parts they used and transcribed the values to the BOM without rounding.
Likely true for the "1.047 uH" toroids, but it doesn't explain the others,
and nothing explains CR3068 as far as I can tell. I wonder if it's an IP
protection feature. If Hickok or Lavoie or somebody like that were to clone
the instrument, things would get awkward if they had to explain what that
diode was for in court. Similar to the practice of adding fictitious towns
to a map to guard against commercial copying.

-- john, KE5FX

If it is purely a (TTL) logic section, it could be that a little diode-logic was added to save a gate package or such, and required a little different biasing to assure proper levels. Often, a Ge or Schottky diode could be used with a saturated transistor output to get a valid TTL-low when isolation is needed, or a regular Si diode could work with some biasing help.

Ed

I got to answer my own question today, it's the 3rd Thursday of the month and I had the day off so I swung by. I found a sign next to the door that reads:
RAMS Country Store is currently closed due to COVID-19
Please check back September 1, 2021

Very exciting! I'm really looking forward to this bit of normalcy returning.

On Thu, 15 Jul 2021, Ed Breya via groups.io wrote:

It is pure logic, ON/OFF. 'LS145 pin active (low), +15V forward bias, pass
diodes in full conductance, those shorting to ground reverse biased i.e.
OFF. 'LS145 pin inactive, -15V reverse bias, pass diodes OFF, those shorting
to ground forward biased i.e. input (after pass diode) shorted to ground,
output (before pass diode) also shorted. Both sides of switches DC blocked
by 10nF ceramics.

There is nothing fancy there. Those are just switches that are either ON or
OFF connecting one of 5 filters between IN and OUT. No fancy p-i-n diodes,
no active parts besides those switches. All diodes are just dumb rectifiers,
not even fast ones (think 1N4001). All filters are totally passive, either
LC or crystal. 10/100Hz has +15V power for thermal stabilization (oven). 4
out of 5 have a trivial gain control (trimpot as variable divider). The
fifth one doesn't have even that, its output level is used as reference to
set other filters' gain against.

There is a dual stage gain block after that (post-VR amplifier) on a
separate board but there is also nothing fancy there -- fixed gain medium
power output stage with 8th order LC filter after it preceeded by a single
variable gain stage. Both are regular common emitter amplifiers with
variable stage using a trimpot in parallel with emitter degeneration
resistor to set required gain.

There are fancy p-i-n diodes and whole lot of other interesting stuff in
494AP but not on that board.

I'm almost 100% sure it is just a snafu that happens all the time and was
quite widespread back then when CAD didn't exist yet but leave 0.00001%
doubt of missing something.

It is probably like e.g. very good vintage Kenwood KA-9100 amplifier where a
small droplet of ink made its way to one channel 10K resistor on the
schematic and made it 1.0K. This went all the way to production and all
those KA-9100 have 10K resistor on one channel final power amplifier board
and 1K on other channel.

BTW, it is not that I need this as a repair hint; it is just out of
curiosity.

There is another fancy thing -- IN has a ground bias return make of series
connected 64uH inductor and TWO 330 Ohm resistors while OUT has a single 680
Ohm resistor instead of those two 330 Ohm ones. Once again there is no
particular reason for that. There is no high voltage there (-2dBm level AC
signal, DC blocked by a 10nF ceramic capacitor), no high power, no
especially high frequencies (it is 10 MHz IF) and those resistors are crappy
1/4W 5% carbon film ones.

I don't know the circuit here, but you may want to look at the logic and
PIN control circuits and circuit descriptions in more detail. Sometimes a
couple extra dB attenuation or passing, depending on the situation, makes
things work much better. It may boil down to turning on a PIN harder, to
short signals to ground, or to get a little more through signal, in
certain spots. Also note that in many setups, the Q (hence BW) of the
crystal RBW IF filters is set by variable PIN RF resistance (DC control
current), so that aspect has to be handled in the overall biasing scheme.

---
*
* KSI@home KOI8 Net < > The impossible we do immediately. *
* Las Vegas NV, USA < > Miracles require 24-hour notice. *
*

Thank you Jared, I've sent a pm to arrange shipping details etc..

David

Not a dumb question, but changing the mobo in a Waverunner Xi is apparently somewhat of a challenge.

It also needs to work with XP embedded.

David

I don't know the circuit here, but you may want to look at the logic and PIN control circuits and circuit descriptions in more detail. Sometimes a couple extra dB attenuation or passing, depending on the situation, makes things work much better. It may boil down to turning on a PIN harder, to short signals to ground, or to get a little more through signal, in certain spots. Also note that in many setups, the Q (hence BW) of the crystal RBW IF filters is set by variable PIN RF resistance (DC control current), so that aspect has to be handled in the overall biasing scheme.

Ed

that was supposed to be shifts and xors

This might be a dumb question, but why not get a different motherboard?

On Thu, Jul 15, 2021 at 6:46 PM David C. Partridge
<david.partridge@...> wrote:

I have a scope (not Tektronix or HP/K/A) that uses the BCM MX855 mobo with a
1.3 Celeron.

I'd like to give a late life performance boost and an told a Pentium M765
will do the job and maybe even an M780 (though that may depend on BIOS
levels).

Can anyone help? If you also have stick on PC2700/PC3200 1GB Ram that would
be great too!

Thanks
David

That sounds like a plausible theory, all though, what you described as a crc is really a checksum. A crc is similar but much more stringent. It is a polynomial with a characteristic divisor. In implementation is it is a bunch of shits and xors. None the less, that does not affect your theory, it works somewhat the same but the crc for target image must be calculated and then compared to the one in the last number of bytes depending on whether it is a crc8, crc16, or crc32. On the other hand the life time of those modules is 10 yr. About 30 yr ago I wrote a lot of 8051 code and designed a bunch of circuits to do all that. Back then 10 yr seemed like a lot of time. I think this scope is a mid nineties as its serial number is B4xxxx which is the later variety.

Anyhow I need to find out how up/download a new image. As I said above, I am getting an ieee 488 and I have an image I found posted. After that I can see if the same thing happens when power is removed, if so the module battery is bad. I would have thought running the SPC would have written a new freshly calculated crc. Seems like a flaw in the design. I always incorporated such features into my designs as I had an original IBM AT which used the original Mot chip the Dallas module was based on. The original design had a circuit bug that caused the battery to go dead regularly and so even though Dallas fixed the bug in the module, I always incorporated a convenient work around as sometime actions of users drained them. In the end the module was just a bad idea as can be seen now. Something custom that becomes obsolete changed out for something standard that will live seemingly forever.

Bert, Jeff, and Albert, thank you for the response.

Bert, I am planning on replacing the line caps. Seems to be the No.1 item to address during my research. Definitely not leaving that out! I have also heard that I should check the resistors in the focus string, that is also definitely on my list of things to do.

Jeff, I can appreciate that adage in certain situations, but I know that this scope was used in a university setting which makes me wager that it has a significant amount of hours on it. Not so much it is worn out, the interior is actually fairly clean, but in my (somewhat limited) experience, replacing electrolytics are a good PM measure especially when there is a fair chance they have seen some use (and have reached what many consider a ripe age).

Albert, on the topic of the pot, that is what I am thinking as well. I just want to see what kind of signal the two pots together send to the MUX. In regards to the screen at power up, I was not aware that this a cal screen. When the scope powers on to that screen, no control input gets me past it.. It could be related to my cursor control? Have not gone that far yet. But since the cursor control is essentially useless as it stands, I bet it has something to do with it. The few times I had traces, the cursor was so erratic that it made the scope seem to have a mind of it's own. Hopefully a good cleaning can get it working for the time being.

Again, thank you everybody for the help. I really appreciate the time you are willing to share with me.

On Thu, Jul 15, 2021 at 01:10 PM, sweetbeats wrote:

The rear interface output of the SG 502 will be connected to the rear
interface input of an AA 501A located adjacent to each other in the TM 504
frame. Is it necessary to use coaxial cable for this interconnect, or is it
acceptable to use standard stranded cable?

I used coax but even so the environment back there is so electrically noisy that the THD measured via the backplane is significantly higher than when connected around the front with BNC cables.

Beware that using pins on the righthand module can foul the module when inserted. I connected my SG505 on the left to an AA501 in the middle and an SC504 on the right of a TM515, and everything worked except the SYNC connection, which was shorting on the scope. Removed the pins and soldered the connection straight in and problem solved.

EJP

Can somebody come out with any reason for the CR3068 diode on VR 2nd Filter
Select board (left bottom corner on the schematic on page 185 of 494A/AP
Vol.2 Service Manual)?

There are 5 filters there, each having same exact switch on input and output
made from couple of diodes and a 2N2907 switch applying either +15V for ON
or -15V for OFF via 64uH inductor thus forward/reverse biasing those diodes.
Two switches per filter, on input and output so all inactive filters are
disconnected from both ends.

The switches are driven from an open collector 74LS145. Same filter is
inserted for 1MHz and 3MHz (it is a pass-through with only gain adjustment
potentiometer -- it is SECOND stage filters so actual filter is implemented
in the first stage). To make it happen they tied 'LS145 pins 2 and 9
together so either one would pull the 2N2907 switch bases low thus inserting
that bypass "filter" for corresponding BCD code.

The 100kHz/10kHz/1kHz filters are all separate so 'LS145 3/4/5 pins each
control their own pair of switches.

Then, 10Hz/100Hz share the same filter, exactly like 1MHz/3MHz, but this
time it is an actual filter. That means 'LS145 pins 6 and 7 should be tied
together to implement wired OR exactly like it is done with pins 2 and 9 for
the 1MHz/3MHz one.

Tying OC outputs into wired OR is perfectly fine when active level is LOW,
it is done all the time and this is what 1MHz/3MHz have. However for
10Hz/100Hz they put a DIODE between corresponding pins that is equivalent to
a short pulling the Q2020 and Q8035 bases to ground when either pin 6 or 7
is low.

But that is not all -- all switches are identical with 3.3K resistor to -15V
EXCEPT the one implemented with Q2020 that has 2.2K instead of 3.3K with
everything else EXACTLY identical. That also doesn't change anything as all
those switches are DC-blocked by 10nF capacitors on both sides of each
diodes/transistor switches. Diodes are also identical so there is absolutely
no reason for 10Hz/100Hz part to be any different from 1MHz/3MHz one.

Am I missing something?

---
*
* KSI@home KOI8 Net < > The impossible we do immediately. *
* Las Vegas NV, USA < > Miracles require 24-hour notice. *
*

I have the following CPU's spare if any of these will be of use:

1x SL6F9 - M705
1x SL7EG - M725
1x SL7SA - M740
2x SL7EN - M745
1x SL7V3 - M765
1x SL7VB - M780

I'm sure I could send one or two vaguely in your direction for the cost of shipping etc. :) (I'm in Japan, but it shouldn't cost too much for such a small parcel if you can't find anything locally)

David, here is the chip data. Lots of info to be found using a search. I have several Dell desktops and HP laptops from that era but you need to state if it is a desktop board or a converted laptop. The Dell desktops did use an M series processor even tho it was meant for mobile.?

Hi David I have 8 Pentium, 4 Pentium 3 and 2 Pentium 4. But none
have a M in their markings like M765 or M780.
Have a couple 1 gb 2700 and 1 3200, several 512mb of this speed.
Have 5 AMD processors also.
But I am across the pond from you it seems.
Gary G