Although I did not investigate FR4, I found little difference in performance between 1.58mm FR1 and Rogers RO4003C in the frequency range of interest here.
Also, as Stephen Menasian correctly points out, resistance and reactance should always be summed in quadrature, even in cases where the design result is not impacted (as is the case here) by just adding them. I have updated my original document accordingly.
Good luck with your project!
john
I pulled all the transistors (except for Q958, on the back of the board) from the -15V regulator and measured the voltages at each of their pins. Everything looks good except for the following:
The voltages on the base and emitter of Q958 (the big power transistor) is a bit low, meaning that the -18V rail may be bad. I will need to pull the power supply (I think) in order to check the components of the -18V rectifier path (C811, CR811, and R811).
The voltage at the base of Q943A is about half what it should be (-7.8V rather than -14.9V), but that's driven by the -15V sense, which should be registering maximum feedback in this case (so probably okay?).
I haven't tested the two canned NPN pairs yet (because it's hard to hook them up to the component tester). I have ordered some from an eBay seller, so I should have spares, in case either of these are bad, but I would be interested in modern substitutes for the NS7348. Could I simply pop two discrete NPN transistors (with suitable specs) in the socket and expect that to work?
-- Jeff Dutky
Yes, I can remember 93 ohm coax cables with BNC connectors being thrown out by the hundreds when the Lab went from 3270s to Ethernet connected IBM PCs in the 1980s. I seem to remember that you can mate the 93 ohm plugs with 50 ohm sockets if you are really determined, but it doesn't do the sockets any favours.
Roger
pcb@frankenthalerfoundation.org Notification
The following files have been uploaded to the Files area of the pcb@frankenthalerfoundation.org group.
By: John Bennett <jkbco@...>
Description: Revised to properly sum impedances in analysis section. Analysis results and ultimate design remain the same. Also simplified Eagle hack to print board on Bantam mill.
Greg is correct. I had a reply from Paul on Nextdoor (I have an account) and since the overwhelming nature of this project, he prefers to stay with the FB contact procedure. Definitely no personal email will be divulged. I agree with him. After-all, he is only trying to help the family on his free time. I hope Paul will be successful in his efforts.
On Sun, Feb 14, 2021 at 12:15 PM Charles <charlesmorris800@...> wrote: "?If the original diodes went in clips like the 1S1, you could use my technique. I took a bit of bare FR-4, ground it into a "T" shape with the crossbar fitting the clips, glued the SOT-23 diode in the middle, " Unfortunately they do not. There is a (brittle and now broken) white plastic holder for both the sampling diodes, which slides into a slot in the board. D6 in the manual picture, (D5 is in the same holder on the other side). I want to add as little capacitance and inductance as I can to the SOT package leads, too.
There are good photos of the holder with the diodes in place on the TekWiki page: https://www.frankenthalerfoundation.org The clip would lend itself to SLS printing such as with ShapeWays - I see people printing these clips (https://www.frankenthalerfoundation.org occasionally, and I've never had a complaint that they've failed. It would also be possible to machine a replacement, though it would have to be done in two halves due to the "facial features" on the inside of the clip. How you'd mount your replacement diodes, though, I'm not sure.
"?If the original diodes went in clips like the 1S1, you could use my technique. I took a bit of bare FR-4, ground it into a "T" shape with the crossbar fitting the clips, glued the SOT-23 diode in the middle, "
Unfortunately they do not. There is a (brittle and now broken) white plastic holder for both the sampling diodes, which slides into a slot in the board. D6 in the manual picture, (D5 is in the same holder on the other side).
I want to add as little capacitance and inductance as I can to the SOT package leads, too.
IIRC 93 ohm is the impedance used by IBM 3270 terminals - could be wrong - it's a very long time.
David
-----Original Message----- From: pcb@frankenthalerfoundation.org <pcb@frankenthalerfoundation.org> On Behalf Of walter shawlee Sent: 14 February 2021 16:40 To: pcb@frankenthalerfoundation.org Subject: [TekScopes] 93 Ohm feed-thru terminators - Unobtanium? No, as it turns out. Following this thread, I remembered that I had some odd BNC terminators in my accessory drawer. I just fished them out, and they are ELCOM FT-90, BNC (m-f) terminators and measure between 91.2 and 93 ohms each.
walter shawlee
Following this thread, I remembered that I had some odd BNC terminators in my accessory drawer. I just fished them out, and they are ELCOM FT-90, BNC (m-f) terminators and measure between 91.2 and 93 ohms each. I have 5 of them, and no use for them. They are unused, and look good,, seem to be silver plated with gold BNC p[ins. is $5 each reasonable/? please contact me off list if you want them. I think they are too heavy to go in a padded bag, so that means a small packet, which is around $20. in any case, I have them if they will help anybody. all the best, walter (walter2 -at- sphere.bc.ca) sphere research corp. -- Walter Shawlee 2 Sphere Research Corp. 3394 Sunnyside Rd. West Kelowna, BC, V1Z 2V4 CANADA Phone: +1 (250-769-1834 -:- https://www.frankenthalerfoundation.org +We're all in one boat, no matter how it looks to you. (WS2) +All you need is love. (John Lennon) +But, that doesn't mean other things don't come in handy. (WS2) +Nature is trying very hard to make us succeed, but nature does not depend on us. We are not the only experiment. (R. Buckminster Fuller)
I don't understand this thread, one person is using Rogers, the other is saying 250MHz, these two things are incongruous.
Chuck as always a prefect information. Most of my scopes had the later SMD boards, and the recap and cleanup not difficult. The NVRAM batt is another issue. I have noticed the subtle improvements in the later SN revs, also that a later SN over 050 or even B060 will be a newer machine with perhaps less use. So my preference is the later models.
Jon
?If the original diodes went in clips like the 1S1, you could use my technique. I took a bit of bare FR-4, ground it into a "T" shape with the crossbar fitting the clips, glued the SOT-23 diode in the middle, wrapped each end with a few turns of fine wire?, and soldered to the diode. Why a "T"? To give you something to grip while working on it. It was pretty easy to make four of these.
HTH,
Dave Wise
________________________________ From: pcb@frankenthalerfoundation.org <pcb@frankenthalerfoundation.org> on behalf of Charles via groups.io <charlesmorris800@...> Sent: Saturday, February 13, 2021 5:56 PM To: pcb@frankenthalerfoundation.org Subject: Re: [TekScopes] Checking sampling diodes Thanks for the recommendations. Dan has raised his postage rate to $8.00... and Brad's email address bounced (at least the one on the website you linked, which was updated last in 2008. Anyhow, I ordered from Digi-Key: https://www.frankenthalerfoundation.org (which is their recommended substitute for the HSMS-2812), five at $1.53 each (won't break the bank); and ten of the Rohm RB886CS single diodes I asked about earlier, at only 34.8 cents apiece. Since I ordered multiple spares, that guarantees I'll never blow another one (kind of like carrying an umbrella prevents rain) ;) Any advice on mounting issues? If I have to extend leads I assume a short wide piece of brass or copper foil is the lowest inductance. I think the SOT package will be just a hair short of spanning the gap in the board.
If a "like" vote is considered a thank you, I wish I could vote a few more times.
Thank you!!! larry
Life is surely different dow nun'dah.
Mark
On 2/13/21 8:19 PM, Harvey White wrote: > if you use z axis modulation anywhere, you need a harness, suspension, and a shop crane. > Harvey > > > On 2/13/2021 5:46 PM, Jeff Dutky wrote: > > > > Tom, > > So do I need to replace my bench stool with a cot, or can I just turn the scope 90 degrees? > > > > > > Also, which side, left or right? > > > > > > -- Jeff Dutky
And most importantly, the toilets.
On 2/13/21 7:23 PM, Jeff Dutky wrote: > The water spirals the wrong way out the sink
4 sets of boards made it to Chesapeake Va. on Saturday. Despite our mail carriers effort to break them by forcing them into the mail box, he failed the boards look great!
> Both normal input and trigger path are using same +15V, +5V, -8V in their > pre-amp so power supply could still be a problem.
I missed +8V, all four supplies are used in both Channel and Trigger pre-amps. It is best to look at their ripple again.
Another question I forgot to ask is when you push "TRIG VIEW" what is the amplitude of the noise/coupling compared to Ch1 noise/coupling?
Ozan
> I had found excessive ripple on the +5V and -8V rails, 4mv instead of 2mv, but > after changing the -8V filter cap, the ripple stayed the same on that rail, > and the cap checked good... I didn’t bother changing the 5V volt one yet. > May I didn’t check the ripple right....?
My personal opinion is 4mV instead of 2mV out of a >5V supply is not going to cause what you are seeing. How about +15V supply? Also as Chuck commented it is not easy to make these low mV measurements, you need a very short ground lead connected to a nearby test point ground.
> > 3) If the signal is on both channels and you can trigger: Trigger on Ch1 and > > observe Ch2 as you "invert" Ch2, does Ch2 noise invert? > They both can trigger, but if and only if the trigger source is Line. > Yes, on Channel 2 the noise inverts.
This says the noise/coupling is getting into Ch2 pretty early on, polarity switch happens in the first hybrid. However, see my comments about "TRIG VIEW". The supplies at this stage are +15V, -8V, and +5V. How clean was +15V? Coupling at this stage could be something else than supplies, there is a lot of gain to amplify any coupling at the input.
> > 4) If you look at Ch1 output on the back with another scope do you see the > > ripple at Ch1 output? > Yes, I do: https://groups.io/g/TekScopes/photo/260052/0?p=Created,,,50,2,0,0
This again points to coupling early in the chain like the test #3. Did you make the connection with a BNC cable between two scopes, set to 50-ohm?
> > 5) If you switch to trigger source to Ext or Ext/10 and push the "TRIG VIEW" > > do you still see the ripple? > Yep, I can.
This is unexpected. #3 and #4 points to coupling early but when trigger source is Ext and "TRIG VIEW" is pushed all of the stages in #3 and #4 are bypassed. Only external source is shown, Ch1 and Ch2 are not shown. This is the behavior I am seeing on an 485, someone with 465B should try the "TRIG VIEW" button to confirm.
Unless there is a problem with "TRIG VIEW" this means two different coupling paths. You can confirm if TRIG view is working by applying a signal e.g. at 1KHz at External Trigger, applying a 2kHz signal at Ch1/Ch2 and pushing the "TRIG VIEW". You should see only the 1kHz (or whatever is applied to External trigger), this is what happens on a 485.
Note that on w140 site service manual is missing one of the schematic sheets. That page is a separate file: https://w140.com/465b_trig2.pdf
> Diagnosis? Vertical amp has an issue?
I am puzzled by the "TRIG VIEW" still showing the noise/coupling and Ch2 invert button inverting the noise/coupling. One says coupling is early in the chain, the other says coupling is at the later stages. Could you confirm "TRIG VIEW" is working? It makes a big difference in where to look at. BTW, "TRIG VIEW"only works if trigger source is Ext or Ext/10.
Both normal input and trigger path are using same +15V, +5V, -8V in their pre-amp so power supply could still be a problem.
Well, I think I might have crossed the streams while trying to measure the voltages in the -15V regulator.
First, I pulled Q952 and Q956 and tested them on my component tester. They seemed to test okay:
Q952 = PNP, hFE 187, Vf 676 mV
Q956 = NPN, hFE 143, Vf 653 mV
I put them back in their sockets, powered up the scope, and proceeded to measure voltages at each pin of each transistor,
