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My goal is to unlock the secret of how the AM503B works and ultimately to
find the schematic, theory of operation, maintenance manual, etc. so we can
finally fix the plugins.


I am looking into the unusual parts in them at the moment and these 3 parts
are the most puzzling.


1) 160-9569-02. My wild guess is it is a PROM holding a program. For what
processor it might be I have no clue.


2) 165-2456-00. This is a Hypcon package from MAXTEK. I would guess it is
the ASIC running everything that isn't in discrete transistors or TTL glue
logic.


I cannot find any reference to these two entire categories of parts: I have
no parts catalogs that show 160-xxxx-yy or 165-xxxx-yy parts. I don't even
know what a 160 or 165 part could be. Not even a wild guess. I don't even
know if there is a catalog of those kinds of parts. Does anyone know?


3) Finally I have what looks to be a specialized microprocessor (wild ass
guess). This would be an IMP (International Microelectronic Products)
I10412-01. It is a 28 pin SOIC. They are no longer in business as near as I
can tell. That isn't a Tek part. It is not a company I ever heard of. There
is virtually no reference to it anywhere on the internet except it might be
called a "daculator" (that is not a misprint as far as I know) and it might
be related to a Tek 156-6224-00. All Microprocessor, TTL, special function,
etc, etc chips start with 156-xxxx-yy but my Tek IC parts catalog stops
around 156-3000-yy so I have no information on it.

Hey Lol,

Your nice old 485s come equipped with graticule markers specifically for
rise time measurement. See this video <> for
how to use them to get repeatable and comparable measurements between
scopes and signal sources.

Siggi
On Mon, May 21, 2018 at 19:46 lop pol via Groups.Io <the_infinite_penguin=
[email protected]> wrote:

On Mon, May 21, 2018 at 03:57 pm, Raymond Domp Frank wrote:

Hi lop pol,
Thanks for doing the tests. I don't understand the outcome, however.
Just looking at your images:
In the TD (tunneldiode pulser) image, assuming a TD rt of 100ps (<=125ps
specified), I see a 600ps rise time (rt), indicating about 590 MHz bw of

the

485 against a spec. of 350 MHz. Even for that 'scope, it seems very high

bw to

me. 30% faster than spec'ed would be "normal", but 70%? Even with a
theoretical rt of 0ps for the TD, the 485's bw would be about 580 MHz,

about

65% faster than specified for this model! It *could* be caused by a slow

1

ns/div. time base speed.

A second strange thing is the suggested rt of the PG506 (pg). I see a rt

of

1.6 ns. Assuming the specified rt for the 485 @ <= 1 ns (350 MHz), the

pg's rt

would be 1.24 ns, against a spec of < 1 ns. Not so good but possible,

since

the later (towards the top) part of the edge shows a speed reduction

(shoulder

rounding) that is not typical for this instrument. Also, the amplitude

on the

screen is a bit higher than used for the 485's specification, which could
result in it performing a bit slower. Also, using the pg's variable

attenuator

would reduce its rt. BTW, the "slower shoulder" could be a side effect of
using the attenuator pot to reduce the output signal!

So, two things I don't quite understand:
- Exceptionally fast (high bw) 485
- Exceptionally slow PG506.

Unless I'm mistaken in my observations, I don't see how to reconcile

them.

Raymond

I have added another 485 for our assessment.
067-0681-01 /g/TekScopes/photo/50828/2?p=Name,,,20,1,0,0
and pg506 fast rise
/g/TekScopes/photo/50828/3?p=Name,,,20,1,0,0

correction:
"ratios of source and load impedance in the range ten to one to one thoudsand to one are
common" not "ten to one" as I stated earlier.
My attempt to interpolate replies with bold italic text didn't work so I'm trying again with a font
change......
On 21 May 2018 at 15:16, Ted Rook wrote:
My experience in the lab tends to roll-off above 20kHz so there isn't much I can usually
contribute to threads here however I wish to offer some remarks in response to soome fuzzy
information below.
Ted
On 21 May 2018 at 7:56, KeepIt SimpleStupid via Groups.Io wrote:
This

might help you understand where the 600 ohms came from.
It's unlikely that a consumer grade piece of audio equipment would be able to drive a 600
ohm input.
In the commercial sense, connections are usually balanced XLR's using 600 ohm
transmission line.? You do have long cable to deal with.
In audio transmission lines are not used. Rather the system operates
with low source impedances and high load impedances, ratios of ten
to one to one are chousand to oneommon. This is true for balanced
and unbalanced operations.
The only real object is to have x volts p-p at the end of the cable, so you drive with the lowest
impeadance into something reasonable like 10K.? Tubes were an entirely different animal.
With a power amp, you have say an 8 ohm speaker and 100 W/ch, both channels driven.? If I
had an 8 ohm output Z at my amplifier that would not be very good.? So, I really need the
lowest output Z.? This is actually expressed as Damping factor.? A damping factor of 100,
means the output Z of the amp is 8 ohms/100.
Speaker impeadance is actually measured at 1 kHz and is usually about 6 ohms for an "8
ohm speaker".
It is the minimum value of the impedance that matters from the point
of view of power amplifier loading. Speaker impedances vary
substantially over the audio frequency range usually being a minimum
at the frequency at which the driver low frequency resonance occurs,
often in the range 20-100Hz. A value of 6 ohms means the minimum
impedance is 6 ohms, this is not the impedance at 1kHz, which is
probably much higher, and irrelevant.
We also have losses in the wires going to the speaker.? We don't have sense leads in our
audio amplifiers.
Professional audio is usually more precise.? So, the output is assumed to be driving a 600
ohm balanced load.? That's not the case in consumer audio.
Balanced operation is common in professional audio but loads are 10k
or higher. 600 ohm loads were encountered mostly in telephony in the
days when it was analogue, but not in audio where they were rare,
and are now non existent.
==
A comment about scope impeadance.? Two standards exist of 1 M and 50 ohms.? They may
have different parallel capacitances.? 1M || 22 pF is common.
Why the capacitance?? We try to create the perfect voltage divider.? So of the scope has 1 M
|| 22 pF and the probe has 1 M || with x-22 pF, then it's possible to create a near perfect
divider at "all" frequencies.
? By doing probe compensation (vary the capacitor on the probe with a square wave input
such that the waveform is square) does just that.? In return, we get a probe that sees 10 meg
ohms resistive and attenuates the signal by 10x usually. ?? The scope probe cable has
capacitance too.
==
You also need to remember a couple of things:
Twisting helps eliminate EMI because the EMI radiates into both conductors "equally" and the
differential receiver removes the common mode signal as well as the act of twisting.
Shielding reduces EMI.? Shields should be connected at one end only and this is typically the
signal source.
Thus, twisted-pair shielded cable is very common for process control and professional audio
too.
Ground loops are really our enemy.
A square wave by Fourier analysis requires infinate bandwidth to re-produce.
It's made up of the sum of the odd harmonics of sine waves.
Bandwith is usually measured at the -3db frequency or when the signal is down by ~0.707.
there is a rule of thumb that relates rise time and bandwidth.? See:

-The-bandwidth-of-a-signal-from-its-rise-time
Worry about stuff when it's important.
Is three resistances in series e.g. 3K equivalent to three 1K resistors in series??? I can argue
no and be right.
Does a moving wire in free space on earth develop a current???? The answer is yes.? The
practical answer is no.? It is a wire that's rotating in the Earth's magnetic field, so it generates
a current based on physics.? Have I measured such a current - Yes.
In a college glass we had a test and I successfully argued that my answer was correct. ? His
answer was, "Your not supposed to know that yet."
On Friday, February 16, 2018, 6:00:25 PM EST, nielsentelecom@...
<nielsentelecom@...> wrote:
In telephony, bridging is a common concept. The impedance could be
anything. on repeater equipment, there is a switch setting if the unit
was at the end of the trunk, or in the middle somewhere. The settings
are; 150 ohm, 600 ohm, or 1200 ohm. The 600 is the usual setting. The
1200 ohm is considered a compromise setting. You have to be careful with
the settings. Setting 1200 ohm can cause overdriving an amplifier or
repeater with the usual accompanied distortion or 'ringing'. When
sending test tones to check level, or realigning a circuit, the
transmission test set had to be set properly to either 'terminated' or
'bridged' to measure the tone correctly. Otherwise a bad reading will
result.
I've always thought the term came from the schematic drawing of a
bridged circuit, 2 parallel lines and 2 perpendicular lines crossing the
parallel lines. It looks like a bridge at the crossing points.
I use the term 'bridged' to describe any paralleled devices. Such as
duplex wall outlets.
NielsenTelecom