I love my oscilloscope almost as much as one can love a machine...

My oscilloscope is *both* analog *and* digital.

This ain't no small potatoes...

We're talking: Its "bandwidth" is 20MHz, but I've diagnosed signals up to 128MHz, by adjusting various scaling-factors, in analog-mode.

In digital mode... well, it's pretty limited. 20MS/s means Nyquist would say we can't view anything greater than 10MHz, and then, only *barely*. Allegedly it can view repetitive signals at much higher sample-rates in "EQUIV" mode, which I assume does-so by *beginning* sampling at different delays after the trigger... I've had... sporadic luck with this.

But... at signal-rates lower than 10MHz, the digital-mode it does quite nicely... E.G. being able to "scroll" low-frequency signals is *awesome*... and, as far as I'm aware, completely impossible via analog-only means. Similarly, the ability to "hold" and then, essentially, "dump" a screenshot... well that's quite handy. It also does averaging and various interpolation-methods, but not things like... what I'mma call "windowing" wherein it'd show both the min and max values sampled at each sample-point (limited sample-memory, only seems to handle about one screen).

Now, in this era a 20MS/s 'scope ain't hard to come by... (nevermind RAM)... And, if I understand correctly, most digital 'scopes today that claim e.g. 20MHz sample at 10x that (200MS/s). So, by-far way better than this guy... (Though, there is a bit of debate as to whether cheapo-'scopes that claim such rates actually have the analog-front-ends to support it).

Anyways, I *have* actually diagnosed 128Mb/s signals, of certain forms, on my allegedly 20MHz analog 'scope... aliasing isn't a factor in the analog realm... It Can Be Done... And, so, analog is quite a nice thing at times...

(E.G. say your "20MHz" digital-only 'scope samples at 200MS/s... Nyquist says that you'll never see anything greater than 100MHz on that screen, without its being severely distorted by aliasing... Though, again, there may be ways 'round this, e.g. when you know a signal is repetitive, and your triggering is highly-accurate, and your software-programmer and circuit designer were "extremely" on the side of "clever").

.....

Anyways... It's been a long-running idea to replace the digital circuitry in my 'scope with something a little more capable in today's technology... 

I've yet to come across a service-manual (as opposed to user-manual) for this guy, so I guess we'll have to start with some reverse-engineering...

.........

Oh, BTW, this is a Goldstar OS-3020, which appears to also have been labelled as LG (Lucky Goldstar?) OS-3020, also plausibly EZ-Digital OS-3020, It's of the OS-3000 series (which comes in 20, 40, and 60MHz varieties, along with the OS-3040, OS-3060... And I've seen e.g. OS-3020D, OS-3040D, and OS-3060D part-numbers, as well...

The user-manual shows BASIC listings for how to work with it... I mean, Cool. No?

......

Anyways, lacking schematics, here's some stuff for posterity:

The digital-board is located under the CRT... I guess the CRT's sheilding makes that possible.

The "big" components on the digital-board are:

U2412 HD64180RCP 10X (CPU, 10MHz, ZILOG Z180/Z80180 "fully-compatible", 1MB address-space... kinda funny I've been doing so much with Z80's recently. @Ziggurat29, any interest in disassembling this thing?).

U2402 XILINX XC2018-70 (Gate-Array... ??? Video-controller ???)

U2422 EPROM: TMS27C512-15 (Boot-ROM, 64KB)

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Also:

82C55 - (2x) Programmable Peripheral Interface

82C54 - (2x) Programmable Interval Timer

HM63021 - (2x) 2KByte "serial-access" SRAM

[H]A19211B - (2x) 20MS/s 8-bit A-D converters

KM62256BLG-10 - 32KByte SRAM

MC145406 - RS-232 transceiver

319 JRC A3067A - UNKNOWN (LM319? 14 pins...)

Other chips seem to be regular ol' 7400-series and 4000-series

....

Onboard markings:

511-542-ABC DIGITAL B/D 20 40 60

(Do the 40 and 60MHz units also have only 20MS/s?!)

Ahh... there are a bunch of potentiometers for Gain and Offset... I bet if I adjusted these right, the signals in Analog and Digital modes would both be aligned... They do have a slight offset...

Hah, there's also potentiometers for H/V Gain/Center

Sample/Hold Adjust

EQS Gain/Cent. (maybe for EQUIV mode?)

and Cursor Offset.

(Wow, lotsa Pots on a digital-board!)

Actually, in the grand-scheme of things, it's not too badly-labelled...

Only one of the *NUMEROUS* headers has labels for each pin (Power)

But that's *way* more than most boards I've seen...

P3009: 1: 55V, 2: +12V, 3: -12V, 4: 5V, 5: GND

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(TODO: These photos are shitty... Eventually scan, maybe? Also, there are some others, but aren't yet "internet-friendly" what with my younger-self having decided to write my name on things.)

( !!!! TODO !!!! WHAT THE HE** HAPPENED TO MY PHOTOS?! )

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Various thoughts on improvement/hacks...

X/Y mode doesn't exist (WTF?!) in digital-mode. (WTF?!)

Higher sample-rates, obviously... high-speed ADCs ain't cheap...

Higher sample-memory for e.g. "windowing"... maybe to the level of eye-diagrams?

(How to vector-draw this...?)

Wonder how fast that vector-drawing really is...

And what's responsible for it?! I see ADC's, but no DAC's!

10 headers(!), some with quite a few pins... There's obviously one, with a lot of pins, for the user-interface (buttons, LED), and another for the display... another for sample-data/channel-input... another for power... but that only accounts for, say, 4-5 of the ten.

TODO: Does the "analog" portion still work when the digital board is completely removed? (If not, the analog signals go *through* the digital board, which might make sense what with the time-muxing of the signal and cursors, etc. OTOH, would mean some high-frequency signals are going some long distances, through various boards, before reaching that screen!)

In the digital-realm... there's quite a bit of room for improvement... USB->Computer for screenshots, plausibly saving to SD-Card, or quite a bit more. Plausible tie-in to Sigrok? Onboard spectrum-analysis?

Also many possibilities in the realm of touch-screen and/or quadrature-encoder input... Keyboards are nice... A secondary/fold-out screen...?

With a CRT this thing's a beast... but I'm not sure I'm ready to sacrifice my ability to use analog-mode.

(Interestingly, I think it uses vector-drawing when in digital-mode... vector-drawn CRTs are bad-ass.)

(Also interestingly: It displays some digital-data when in analog-mode... e.g. the cursors... again in vector-mode, and somehow time-division-multiplexed with the analog-display, which *sometimes* causes some interesting artifacts)

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On that note... the digital circuitry does display some data while in analog mode... what sortsa things would I like to view in analog-mode... (as well)?

One thing, for sure: Rail-indicators. When the input-signal causes the internal circuitry (amplifiers, etc.) to hit (or be near) the voltage-"rails." This one I've had taped to the side for quite some time.

Also, maybe some sort of automatic voltage-detection...? The cursors might adjust automatically to a peak (or average-peak) voltage...

(TBC)