RLC meters

That worked. Thanks!

Know where I can find a schematic?

Should be in the manual - it is in the one I downloaded for my 2236.

Ed

Thanks for that tip, Ed. I think my 2235 is the same scope sans the digital multimeter. I downloaded the 2236 manual and I now think I know pretty much where the problem must lie. Could be something as simple as a badly-seated connector since a clock signal is generated on one board and used to toggle a 74F74 on another board.

I know it isn't worth the trouble to fix an old scope like this, but I just hate to trash an otherwise good scope if I can fix it without going to heroic measures. I know a guy who wants a scope, doesn't have to be SOA digital or anything. A lot of barter goes on in the oldfart network. I got the scope from a fellow OF who found it for free as surplus. He sent it to me. I help him with some of his projects now and then. The guy I'll give it to (if he still wants it) can help me out with this 'n that at the lake since he lives there. It all comes round one way or another.

If you're lucky, some of the circuitry might be very similar. But the

2236 might be quite different from the 2235. (I can't say I really know. I refurb'ed and sold dozens of 2235 models, but only one 2236. And I didn't even open the case on the 2236. But the 2236 certainly LOOKS very different than the 2235, and is also worth significantly more $, at least if the display in the fold-down panel cover is still working [they were failure-prone, due to the flex cable].)

Jim Yanik (an ex-Tektronix tech) and a couple of other guys in sci.electronics.repair might be able to give you some specifics, and/or some repair ideas.

I'd definitely also go to

and search the message-archive for the make and model (It's truly a goldmine, for ALL kinds of info!). Try searching for both the 2235 and 2236; maybe use a search like "Tek* 2235 OR 2236", or "Tektronix 223*", or "Tek OR Tektronix 2235 OR 2236" (without the quotes, of course; and the "OR" must be uppercase), etc, etc. Oh: You should add " -FS -sale -FA

-auction" to your search string, to filter out most of the "for sale" and "for auction" messages.

Another *great* place, where you can get the real lowdown on anything Tek, is in the TekScopes group, at

. There are some ex-Tek engineers and field-service guys, there, some real legends (e.g. Stan Griffiths, who wrote a book on refurbishing old Tek scopes, and has a collection of them that fills a warehouse, as well as Deane Kidd, who has literally tons of NOS Tek scope parts and manuals. Both are ex-Tek employees.), and a whole bunch of other extremely-knowledgable and helpful guys.

In either case, give as much information as possible, in your initial "help" request.

Good luck!

- Tom Gootee

"He who lives in a glass house" should not invite "he who is without sin".

Got home today at about 1700, found box in mail. Opened box, started assembling the kit. I had it assembled and operational by 1815.

I love it! It ain't perfect, but it is unquestionably worth $99. Thank you for the tip.

Imperfections:

1: it doesn't operate at a fixed or known frequency, does what it wants. Freq on a 300 uH inductor was about 50 KHz.

2: it probably won't do well with R's or C's of high dissipation. The seller says that up front.

3: it could get confused with an inductor or xfmr having a self-resonant freq near the freq it chooses for testing.

I can live with and work around all of those issues. This will be a very welcome addition to my bench.

BTW, for the big bux guys, the seller offers this fully assembled for another 30 bux. But then, the big bux guys can afford really good instrumentation, right? $2K is just a few chargable hours.

My time is free to me and friends now that I'm retired, and I enjoy slinging solder. YMMV.

Glad you like it! I wish the display had a little more contrast. That hasn't bugged me enough to do anything about it, so it is a minor annoyance. (Yes, I adjusted it to max.)

There's another piece of gear you'll probably love if you don't have one - a capacitor ESR tester. Don't buy one - you can build one easily and cheaply that works great:

I put it in a plastic case and glued on a piece of PC board blank with a slot milled in the copper, so I have 2 copper contact plates. That way, I can pick up a loose cap and touch its leads to the plates to get a reading, or use test leads to check caps that are connected in a circuit.

Ed

See also Elektor 2005 September "ESR/C Meter"

Can't beat that for simple! I like your variant.

This design obviously treats the reactance of the cap as neglible -- a reasonable assumption for most filter caps at 100 KHz.

I'd still like to build some sort of R-X meter or vector voltmeter with user-selectable frequency. Why? (Homer will surely ask that...) Well, just for the hell of it perhaps. It's on the list for the "shop season" that's growing ever closer as the days grow shorter. One unknown so far is what to use for I and Q synch demodulators (baseband detectors) at 100 KHz and maybe 500 KHz with <

1 deg phase error. Maybe 4066-type switches or more modern versions would suffice, maybe I'll need to go to Gilbert-cell devices ala MC1496, the more current AD device, or something. Can't be too hard at 100 KHz, just gotta read some datasheets. I don't do DSP and have no intention of learning, nyaahhh. That's too hard for the likes of me. Hell, I can just barely do PIC or AVR.

Another fellow sent me that as well. Thanks!

What the hell, grab a flashlight. Luxeon -based flashlight, of course! I have a flashlight next to my microscope, another at the lathe, and always one in my pocket. Luxeon-based, of course...

BTW, an immediate app for this little LC meter will be to measure the inductance of the four 17-foot 8-gage wires going from the batteries in the stern of my boat to the trolling motor socket in the bow.

I made a dirt-simple 50% dutycycle PWM to reduce 24VDC down to 12VDC (average, no filtering) to drive my 12V boatlift motor off the 24V TM socket. Current drain steadystate is about 43 amps, probably not a lot more starting surge because of the nature of the beast. I used

120-amp MOSFETS.

The box didn't even get warm. The boat went up, the boat went down... but then it wouldn't go up again. Kaputski. KIA. WTF, over?

Then I calculated the inductance of 17 feet of 8 gage wire. Oh my! About 8 uH per wire and there are four wires. There's surely some field cancellation in the parallel wires, but who knows how close together they are in the hull. Mechanical switch on loadside opens, no prob on output side -- but I bet there was one hell of a spike on the supply side. Pfffft! Post mortem shows that the halfbridge FET's are dead, no charring but clearly dead. They could probably handle the avalanch energy but the 24 V supply was there to finish the job once a spike had punched a path. Oopsie!

So now I want to measure that inductance to see just how bad that problem is and what it might take to fix it in terms of capacitance and/or transient suppression. It may take more than I'll want to bother with.

What I'll probably do is fuggedaboudit and continue to run the lift winch off of just one battery and maybe rewire the plug twice a season to distribute the load history between the two batteries. (There are lines from both batteries to the TM socket) Takes 5 minutes to rewire the plug and I can do that when it's too windy to go fishin'.

see here for a free LC meter...

"ehsjr" a écrit dans le message news: dF1Pg.1533$o1.888@trndny04...

Qu'est "Ce montage permet la mesure des capacites et des selfs, de qq pf au micro farad, et de qq nH au mH."

qq?

4066 is fast enough but not the right tool for the job. Diode bridges (mini-circuits etc) and transistor bridges are plenty good enough, just pick any reasonable one. The hard part is the IQ local oscillator. you will have to pick a reasonable part for that too.

--
 JosephKK
 Gegen dummheit kampfen die Gotter Selbst, vergebens.  
  --Schiller