Well, I have a day job.
I received my SD-24, but it doesn't work right. It has a nasty whoopie-doo in the step response of both channels. Looks like the blowby settings are seriously wrong, but they can't be set from any scope I have.
John
Hi John,
I know, I was just getting worried that you were getting super busy or something and might not have time to look at my SD-24 and that it would be better to wait or something before dropping them in the mail. I do very much appreciate your service here!
:-( That sucks... Hopefully that guy will refund or replace them for you promptly.
---Joel
Send it along. It only takes a couple of minutes to check it out.
He's agreed to swap it for another one, so maybe everything will be OK.
One common failure mode of these things is a dead eeprom chip inside. That's where all the cal factors, including the blowby compensation, are stored.
TEK never published schematics on this series. The service manual says keep it clean and send it back if it's broke. Most of the active parts are on one giant ceramic-substrate hybrid.
Here's the guts of an SD20:
ftp://66.117.156.8/SD20.zip
John
That's almost sad, to see a $0.79 part take down a multi-thousand dollar head. I suppose that, if one has the facilities, making a backup copy of it is prudent.
It's amazing to me how fast those things operate (40GHz!) given the time in which they were designed; I expect they figured keeping the schematics private was a big leg up on the competition.
Of course, since they don't even build them anymore and the folks at, e.g., Pulse Labs have built 100GHz samplers, at this point releasing the schematics would be a great gesture on Tek's part that wouldn't put them at a competitive disadvantage. I'll cross my fingers...
Cool... great pics!
This guy:
So I'm still waiting for more to show up...
---Joel
I have a couple of dead heads that may well have bad eeproms. I suppose I could buy new chips and copy the contents from a known-good head. Might work.
I must have 25 or so heads by now, theoretically worth about $350K according to Tek's last pricing. I think an SD24 was $14K or so. And maybe 10 frames, another $300K or so.
It was Picosecond Pulse Labs. I never figured out why they went to all that trouble, and who they expected to buy the heads. I offered to collaborate on a scope design, but they ignored me. I've heard that they have recently shut down the operation in Oregon that made the 100 GHz sampling heads.
There's not a lot of use for a 100G head. Signals that fast really don't travel through coax or connectors very well. Agilent and Tek could certainly go well past 100 GHz, but have apparently called a truce at 70.
Keep looking. Good deals come up fairly often. And I know a trick which I can convey privately.
John
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