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On Sat, Jan 2, 2021 at 10:08 PM, Steve Goldstein wrote:

Jared,

Your manual lists S3 as 4P6T. Entering that part number in Digikey shows it
as 2P6T. Is there a typo somewhere?

On 1/2/2021 01:14, Jeff Dutky wrote:

Tom,

I measure 2.6 K ohms between the two non-wiper terminals, but the pot is still in circuit, so this is really measuring everything that bridges the +50 V and ground planes in parallel, so is this a meaningful measurement?

It seems like I've eliminated every other possible suspects, and I don't have any other explanation for the measurements I've gotten for the pot resistance (but what the heck do I know? Am I wrong about what I expect to measure on a 25 K ohm pot?).

But I've come this far, and this scope was never meant to be anything other than a parts mule, so taking it down to the studs seems like the logical next step.

-- Jeff Dutky

On Friday, January 1, 2021, 10:31:31 PM PST, Jared Cabot via groups.io <jaredcabot@...> wrote:

On Sat, Jan? 2, 2021 at 06:29 AM, Larry McDavid wrote:

Note that Jared has updated the main PWB Gerber file and the Instruction
Manual file; if you downloaded those earlier, you need to get the new files.

Jared and I are discussing how best to order these sets of PWBs. He is
familiar with the ordering details specifying board material, plating
and edge chamfering so I welcome his support on this. I will order the
board sets and repackage and ship them to those who commit to the
purchase. The produced boards should look like those in his YouTube video.

One small addendum to this, the PCB's will likely not be black as that is a premium option that adds significant cost. They will most likely come in the usual green (more period accurate! :) ) to save as much on cost as possible.
In all other respects they will be identical to what is seen in my video and what is in my hand now. I have also confirmed my design is 100% operational and working correctly on multiple mainframes now.
I'll talk to my contacts at PCBWay to see if I can cut a deal for us, but we'll have to be patient for a few days for them to return from holiday.

If we were to simply order say 20 sets of the 4 boards with no other discounts etc, it looks like a ballpark figure will be around $35 per set of 4 PCB's, plus additional local shipping etc from Larry as an additional cost.
This includes gold plating on the main PCB, and hard gold on the edge connector fingers for added durability with the required chamfering (My PCB just has standard gold all over, so the hard gold is an upgrade).
Obviously, the more we get in on the buy, the cheaper it'll become per set.

As Larry stated, we'll be working together to get this all sorted as smoothly as possible. :)



On Sat, Jan? 2, 2021 at 01:44 PM, Michael W. Lynch wrote:

Jared,

Is there a way to easily bring the EBC of each pass transistor to the front
panel?? These transistors are items that often fail and need to be tested,
especially on these old frames.? Not trying to throw a wrench into the works,
but those pass transistors are a major point of failure and they can cause all
sorts of damage to the plug ins when they are bad.? Even if you could add some
pads near the appropriate connections at the rear to allow those of us who
wanted to add such functionality at our option?

--
Michael Lynch
Dardanelle, AR

It would require a redesign as you would need to install switches to isolate the transistors for testing, and provide connectors on the front panel etc. so It is out of scope for this project.
However, I do have an extender cable project in the works of which it would be trivial to add some test points for the transistors. Stay tuned. :)



On Sat, Jan? 2, 2021 at 09:42 AM, Dave Casey wrote:

I have one of the originals, and it is almost certainly "Tek" built as
opposed to built from the plans. For one thing, it has a Tek serial number
label and silkscreened front panel.

Dave Casey

Well there you go, I stand corrected.
Actually, thinking about it just now, I do remember seeing some photos of these units around that looked a little more professionally made than any DIY unit.



On Sat, Jan? 2, 2021 at 09:39 AM, Dave Casey wrote:

I believe the notch filter could be built in any form factor. IIRC it does
not use power from the mainframe, so there's no reason it has to be in a
TM-style enclosure.

Dave Casey

This is absolutely correct, I think it was built into a TM500 enclosure for user convenience as it was used solely with the SG505 oscillator IIRC.
No reason not to save costs of a TM500 enclosure by sticking it into anything vaguely box shaped available to hand. Tupperware? :D

On 1/2/2021 00:32, Jeff Dutky wrote:

I lifted one end of C1374 and tested it with my DMM916. It acted much more like a capacitor than like a resistor: while measuring resistance I could see it charge up (the resistance increased over several seconds till it became open circuit) then I switch over to voltage measurement and watched it discharge from about 1.1 V down to 0 V over several seconds). Using the capacitance measure shows this is a 0.8 uF capacitor, which is in spec for a the 1 uF electrolytic shown in the schematic.

i checked CR1371 and CR1373 in circuit using the diode check mode of the 916 and they both measured 0.536 V forward voltage drop. They look good.

I measured the trim pot (R1375) while C1373, C1374, and VR1374 were lifted. The trim cap has a range of travel of about 280 degrees:

0 deg = 0 ohms
45 deg = 3.1 K ohms
90 deg = 4.8 K ohms
135 deg = 7.0 K ohms
180 deg = 6.75 ohms
225 deg = 4.3 K ohms
270 deg = 2.7 K ohms

The specified value of R1375 is 25 K ohms, and I expect that it should range smoothly from 0 ohms to 25 K ohms.

I also verified continuity between R1375 and both the ground and +50 V rails.

I checked C1373 (the cap in parallel with VR1374) and it measured as 96.5 nF (it's specced as 0.1 uF on the schematic), so that looks good.

VR1374 is not shorted (I didn't check that it's breakdown voltage was 82 V, as I sadly have no way to do that).

This really seems to point to the trim pot as the culprit, which means I need to get the main interface board out. Joy.

-- Jeff Dutky

-------- Original message --------From: "Jared Cabot via groups.io" <jaredcabot@...> Date: 1/1/21 10:31 PM (GMT-08:00) To: [email protected] Subject: Re: [TekScopes] I built a TM500 mainframe tester, and updated the design. Someone might find this useful? On Sat, Jan? 2, 2021 at 06:29 AM, Larry McDavid wrote:>> Note that Jared has updated the main PWB Gerber file and the Instruction > Manual file; if you downloaded those earlier, you need to get the new files.> > Jared and I are discussing how best to order these sets of PWBs. He is > familiar with the ordering details specifying board material, plating > and edge chamfering so I welcome his support on this. I will order the > board sets and repackage and ship them to those who commit to the > purchase. The produced boards should look like those in his YouTube video.>One small addendum to this, the PCB's will likely not be black as that is a premium option that adds significant cost. They will most likely come in the usual green (more period accurate! :) ) to save as much on cost as possible.In all other respects they will be identical to what is seen in my video and what is in my hand now. I have also confirmed my design is 100% operational and working correctly on multiple mainframes now.I'll talk to my contacts at PCBWay to see if I can cut a deal for us, but we'll have to be patient for a few days for them to return from holiday.If we were to simply order say 20 sets of the 4 boards with no other discounts etc, it looks like a ballpark figure will be around $35 per set of 4 PCB's, plus additional local shipping etc from Larry as an additional cost.This includes gold plating on the main PCB, and hard gold on the edge connector fingers for added durability with the required chamfering (My PCB just has standard gold all over, so the hard gold is an upgrade).Obviously, the more we get in on the buy, the cheaper it'll become per set.As Larry stated, we'll be working together to get this all sorted as smoothly as possible. :)On Sat, Jan? 2, 2021 at 01:44 PM, Michael W. Lynch wrote:>> Jared,> > Is there a way to easily bring the EBC of each pass transistor to the front> panel?? These transistors are items that often fail and need to be tested,> especially on these old frames.? Not trying to throw a wrench into the works,> but those pass transistors are a major point of failure and they can cause all> sorts of damage to the plug ins when they are bad.? Even if you could add some> pads near the appropriate connections at the rear to allow those of us who> wanted to add such functionality at our option?> > -- > Michael Lynch> Dardanelle, ARIt would require a redesign as you would need to install switches to isolate the transistors for testing, and provide connectors on the front panel etc. so It is out of scope for this project.However, I do have an extender cable project in the works of which it would be trivial to add some test points for the transistors. Stay tuned. :)On Sat, Jan? 2, 2021 at 09:42 AM, Dave Casey wrote:>> I have one of the originals, and it is almost certainly "Tek" built as> opposed to built from the plans. For one thing, it has a Tek serial number> label and silkscreened front panel.> > Dave CaseyWell there you go, I stand corrected.Actually, thinking about it just now, I do remember seeing some photos of these units around that looked a little more professionally made than any DIY unit.On Sat, Jan? 2, 2021 at 09:39 AM, Dave Casey wrote:>> I believe the notch filter could be built in any form factor. IIRC it does> not use power from the mainframe, so there's no reason it has to be in a> TM-style enclosure.> > Dave CaseyThis is absolutely correct, I think it was built into a TM500 enclosure for user convenience as it was used solely with the SG505 oscillator IIRC.No reason not to save costs of a TM500 enclosure by sticking it into anything vaguely box shaped available to hand. Tupperware? :D

On Sat, Jan 2, 2021 at 01:03 PM, Roy Thistle wrote:

On Fri, Jan 1, 2021 at 06:08 PM, Harvey White wrote:

... needs to make sure that the AC windings [on the frame] are
properly phased and connected...

But why? (Surely, frames didn't leave the factory, with miswired phasing [it's
been mentioned plug-in were non-disposable back in the day!] )
And as to all the gremlins, re-arranging the wiring, before the frame hits the
GoodWill... is that a thing?
Hands up if that's happened to you.

On 1/1/2021 11:38 PM, Don Bitters via groups.io wrote:

Does it look like the pic on the Newark Canada website?



Specs are listed and data sheet can be downloaded.

Don Bitters