You don't generally need impedance matching.? The 'scope input won't load a 50 Ohm source much.? I use a 50 Ohm termination without attenuation and the high impedance of the oscilloscope has negligible effect. If you are handling substantial power you will need an attenuator; the books tell you what the parameters should be.? For 20 dB attenuation you need 45 Ohms in series and 5 Ohms across the 'scope input.? And of course the 45 Ohm resistor has to handle the power. If you are using a 50 Ohm cable, it needs to be in a 50 Ohm circuit, so the attenuator components should be right at the 'scope. Bob --- On Tue, 2/19/13, Cliff White wrote: From: Cliff White Subject: Re: [TekScopes] Re: What use for a 640 Ohm 1x Probe? To: TekScopes@... Date: Tuesday, February 19, 2013, 8:05 PM ? So, I've had the idea of building a 50 ohm fixed 10x attenuator to use inline with a 50 ohm cable. What kind of impedance matching should I use for the 1meg ohm on the scope? On 02/19/2013 07:26 PM, Don Black wrote: It should be 9 Meg ohms. Then 90% of the signal is dropped across the probes 9 Meg and 10% across the scope's 1 Meg input impedance, giving 10:1 ratio. The compensating capacitors across them are adjusted for the same division at high frequencies to maintain the flat response, that's hat you're setting when you adjust for flat square wave with the trimmer. Don Black. On 20-Feb-13 12:18 PM, David wrote: ? On Wed, 20 Feb 2013 00:24:09 -0000, "Philip" ndpmcintosh@...> wrote: >The publication on scope probes mentioned earlier is good and I am working my way through it. I already had it in my document collection and it was on my reading list. > >If I ohm out a 10x 10Mohm probe in the same way, I get about 10 MOhms. I'll keep reading though... I get almost exactly 9.00 MOhms on each of several different x10 probes within reach.

schematics and pictures pls.
I could not find any line receivers that have ecl output, single ended input and trigger on selective voltage.

--- On Wed, 2/20/13, David DiGiacomo <daviddigiacomo@...> wrote:

From: David DiGiacomo <daviddigiacomo@...>
Subject: Re: [TekScopes] Re: tektronix 318 logic analyzer probe
To: TekScopes@...
Date: Wednesday, February 20, 2013, 5:48 AM
















??









On Tue, Feb 19, 2013 at 5:40 PM, cleyson@...> wrote:

Hi David

Fair comment, maybe you could make your own probes but I don't think you could build a 10 channel 1Meg 5pF FET probe for less than the $100 asking price. You need the 25 way micro D connectors, twisted pair cables and a PCB. Been there and done it for a 7D01 and I just ended up with an unreliable and not very usable probe that's at the bottom of the junk box somewhere.

If it ever comes up to the top again, it would be really interesting

to see the board and hear more about the problems you ran into.



It sounds like you were trying to achieve similar performance to the

Tek design. If the goal was just to get a 308 working, it seems like

a much less ambitious design would be OK. I still wouldn't want to do

it, but I think the parts cost would be a lot less than $100.

I'm partial to Advin myself. Alternatively, a decent used Data I/O
programmer.

Happy hunting.


* REPLY SEPARATOR *

On 19-Feb-13 at 10:46 Alexandre Souza - Listas wrote:

Anybody familiar with the Xeltec line of programmers? Good, bad,
indifferent? I see a batch of 'em all the time on Ebay, some going

for

seemingly high prices.

Good programers, but I'd buy Elnec
Ops, I have a beeprog from Elnec :)

If those low profile socket elements are the ones I am thinking of,
they are called Miniserts. I have had at least two incidents now
where a Minisert was open and reseating the lead at least temporarily
fixed the problem.

There is a datasheet for them in the files area:



Q532 (and Q526) are operating as emitter followers. The emitter
voltages for each are low impedance and should be about 0.6 volts
higher than their base voltages at all times. They are just used as
simple voltage buffers.

Trigger B is completely independent from trigger A and is only used if
a sweep mode other than A internal is selected.

From your description I suspect everything is working but that the A
trigger circuit needs to be calibrated:

R534 is used to center the trigger point vertically on the CRT when
R530 is in the middle of its rotation.

R673 adjusts the trigger view vertical positioning on the CRT.

R547 adjusts the trigger level so that it does not change when the
slope is changed.

R565 adjusts the tunnel diode threshold for maximum sensitivity.

On Wed, 20 Feb 2013 02:17:18 -0000, "stan_katz" <stan_katz@...>
wrote:

I know I've let this thread go cold, but I assure members it wasn't out of neglect. For one thing, I was advised to read the manual, and I have been doing so. In the meantime, I had been monitoring the trigger diodes by clipping scope probes on their anodes. I intended on recording waveforms with my digital camera. Alas, I found the camera was fried. Nevertheless, I decided to do some more examination of the Trigger A circuits. I took hold of one of the probes attached to a tunnel diode, intending to disengage it. The instrument was powered on. The probe came off the board, WITH THE TUNNEL DIODE STILL ATTACHED to the probe! The diode had no sign of being soldered in. I turned off the instrument, and pulled on the other tunnel diode, and it came out. No solder. Now it sunk in. Those phosphor/bronze stakes weren't hiding solder pads underneath, they were all sockets! I must have missed that in some FAQ or manual addendum. The only semiconductors soldered in my 475 are small signal
diodes. Who knows if my probes were intermittently yanking out the anode ends of the TDs. I certainly wasn't going to waste members' time by trying to diagnose TD damage. I bit my lip, and purchased two NOS tunnel diodes for $OUCH.00. As least this message would start with good tunnel diodes.

Following David's advise to do a modified 5-40 trigger A calibration from just Channel 1 input lead me nowhere. The scope wouldn't trigger on the 12mv p-p 350khz sine wave I was using to obtain a .32 division height on the CRT. Adjusting R565 had no effect. Lowering the attenuator and filling the screen with the signal also had no effect. I then returned the trigger level to full + ( clockwise ), attenuator down to 50mv, and with the waveform filling the screen, I got trigger lock. I did note, that during the modified 5-40 calibration attempt, there was no sign of the trigger signal with TRIG VIEW depressed. However, with the intentional misadjustments reported above, I could just see some light at the top of the screen in TRIG VIEW. Although I was advised not to start messing with anything but R565, I adjusted R534 in the "misadjusted" state using TRIG VIEW. The waveform came into view, and I could center it. With this set of adjustments, I could now trigger on the 12mv waveform
with the attenuator turned up to .1v so that I could meet the .32 divisions performance called out in 5-40. I thought I was on to something regarding the trigger centering. I esr'ed all the electrolytics in the triggering section. All checked out. A separate check with a VOM didn't show shorted electrolytics. I thought there may be a fault with U520, and given both it, and U720 were both socketed, I swapped them. No change. I haven't been able to find any shorted bypass caps..yet. I replaced Q532, and two resistors that were more than 50% out of spec. No go. One thing that bothers me is that, on the schematic, the emitter of Q532, is pulled up through R535 to +8.2v. I only measure +5.0v. I can't find any errata that verifies my measurement. The 8.2v source is functioning as it is available everywhere else noted on partial A8 schematic with trigger circuit. Trigger level at pin 14 of U520 varies from 1.7v (full + level) to 200mv (full - level). Is this OK? TP526 has a copy of the 12mv
waveform as expected. I'm fixated on the centering circuit, but can go no further. With HORIZ DISPLAY on A LOCK, there shouldn't be any interaction with TRIG B? Right? I suppose trimmer 534 could be bad, but checking that out requires flipping A8. Yeesh! I haven't messed with R673 yet, as my troubleshooting has been with AC coupling only. Should I go there?

I can tell you from experience with switching power supplies that even replacing the fuse with the correct rating can cause more collateral damage if the power supply isn't fully repaired. Doubling the rating can lead to irreparable damage. If anything, I like to halve the fuse rating for the first test.

I would check/replace everything on the gate of that FET the blew up, and any other power transistors that have failed. If there are any ICs controlling that part of the power supply, replace them. Improper gate/base drive can cause instant failure. Also, loss of regulation can cause some spectacular failures.

--- In TekScopes@..., "circuitsandcode" <circuitsandcode@> wrote:

I used the fused circuit of the meter (10A) which is a little over 2x max current.

--- In TekScopes@..., larrys@ wrote:

"circuitsandcode" <circuitsandcode@> wrote:

Would prefer to have a variable P/S to ramp up voltage - but went for
broke and shorted across the fuse (using multimeter measuring amps)
and Q5 went out in flames. I've since ordered a handful of 2SK1018
parts to replace.

Might want to make sure the meter didn't take any collateral damage.
-ls-

?

So, I've had the idea of building a 50 ohm fixed 10x attenuator to use inline with a 50 ohm cable. What kind of impedance matching should I use for the 1meg ohm on the scope?

On 02/19/2013 07:26 PM, Don Black wrote:

It should be 9 Meg ohms. Then 90% of the signal is dropped across the probes 9 Meg and 10% across the scope's 1 Meg input impedance, giving 10:1 ratio.
The compensating capacitors across them are adjusted for the same division at high frequencies to maintain the flat response, that's hat you're setting when you adjust for flat square wave with the trimmer.

Don Black.

On 20-Feb-13 12:18 PM, David wrote:

?

On Wed, 20 Feb 2013 00:24:09 -0000, "Philip" ndpmcintosh@...>
wrote:

>The publication on scope probes mentioned earlier is good and I am working my way through it. I already had it in my document collection and it was on my reading list.
>
>If I ohm out a 10x 10Mohm probe in the same way, I get about 10 MOhms. I'll keep reading though...

I get almost exactly 9.00 MOhms on each of several different x10
probes within reach.

Hi all,
I have a 7L13 Spectrum Analyzer out in the field, it's not in front of me right now but I will pick it up later this week. I've seen the unit and the 'Center Frequency' LED read-out is stuck, and reads '0000', also the same value is being sent to the CRT display. The analyzer is sitting in a 7000 series mainframe and the mainframe works fine in every other way. In fact, the spectrum analyzer works fine, just the 'Center Frequency' display stays on zeros. The 'Tuning' works and adjusts correctly. It is used with a TR-502 and that combination also works, you just don't know where you are frequency wise. You can place a frequency counter on the AUX out of the TR-502 and manually scan the bandwidth and read the frequency on the counter. It appears everything is fine, just the readout is non-functional, or at least stuck on zeros. I thought it was curious the display in the 7000 is also reading zeros too. I will have it in front of me next week but I thought I would see if
anyone had any thoughts before I open it up.


Thanks in advance,
~Michael - AF7U

From: David DiGiacomo
Subject: Re: [TekScopes] Re: tektronix 318 logic analyzer probe
To: TekScopes@...
Date: Wednesday, February 20, 2013, 5:48 AM

?

On Tue, Feb 19, 2013 at 5:40 PM, cleyson@...> wrote:
> Hi David
>
> Fair comment, maybe you could make your own probes but I don't think you could build a 10 channel 1Meg 5pF FET probe for less than the $100 asking price. You need the 25 way micro D connectors, twisted pair cables and a PCB. Been there and done it for a 7D01 and I just ended up with an unreliable and not very usable probe that's at the bottom of the junk box somewhere.

If it ever comes up to the top again, it would be really interesting
to see the board and hear more about the problems you ran into.

It sounds like you were trying to achieve similar performance to the
Tek design. If the goal was just to get a 308 working, it seems like
a much less ambitious design would be OK. I still wouldn't want to do
it, but I think the parts cost would be a lot less than $100.

From: cleyson@...
Subject: [TekScopes] Re: tektronix 318 logic analyzer probe
To: TekScopes@...
Date: Wednesday, February 20, 2013, 12:12 AM

?

Hi



Unused new old stock and comes with a full set of leads.
Price might be more than you want to pay, but you can't make your
own probes for the same money.

Best regards
Chris

--- In TekScopes@..., Gala Dragos wrote:
>
> Hi,
> I've just acquired a Tektronix 318 logic?analyzer, but it came without the pods.
> It's a nice unit, and by the looks of it, it works, well it displays random logic levels on screen as no pods are plugged in.
> Can I make those pods myself ?
> If not, what pods do I need and where do I find them ?
>

From: Cliff White
Subject: Re: [TekScopes] Re: What use for a 640 Ohm 1x Probe?
To: TekScopes@...
Date: Tuesday, February 19, 2013, 8:05 PM

?

So, I've had the idea of building a 50 ohm fixed 10x attenuator to use inline with a 50 ohm cable. What kind of impedance matching should I use for the 1meg ohm on the scope?

On 02/19/2013 07:26 PM, Don Black wrote:

It should be 9 Meg ohms. Then 90% of the signal is dropped across the probes 9 Meg and 10% across the scope's 1 Meg input impedance, giving 10:1 ratio.
The compensating capacitors across them are adjusted for the same division at high frequencies to maintain the flat response, that's hat you're setting when you adjust for flat square wave with the trimmer.

Don Black.

On 20-Feb-13 12:18 PM, David wrote:

?

On Wed, 20 Feb 2013 00:24:09 -0000, "Philip" ndpmcintosh@...>
wrote:

>The publication on scope probes mentioned earlier is good and I am working my way through it. I already had it in my document collection and it was on my reading list.
>
>If I ohm out a 10x 10Mohm probe in the same way, I get about 10 MOhms. I'll keep reading though...

I get almost exactly 9.00 MOhms on each of several different x10
probes within reach.

It should be 9 Meg ohms. Then 90% of the signal is dropped across the probes 9 Meg and 10% across the scope's 1 Meg input impedance, giving 10:1 ratio.
The compensating capacitors across them are adjusted for the same division at high frequencies to maintain the flat response, that's hat you're setting when you adjust for flat square wave with the trimmer.

Don Black.

On 20-Feb-13 12:18 PM, David wrote:

?

On Wed, 20 Feb 2013 00:24:09 -0000, "Philip" ndpmcintosh@...>
wrote:

>The publication on scope probes mentioned earlier is good and I am working my way through it. I already had it in my document collection and it was on my reading list.
>
>If I ohm out a 10x 10Mohm probe in the same way, I get about 10 MOhms. I'll keep reading though...

I get almost exactly 9.00 MOhms on each of several different x10
probes within reach.