TM500 Mainframe Tester construction master thread.


Jared Cabot
 

So, with all the Mainframe Tester PCB's being sent out recently (thanks Larry!), now is the time for a construction thread for all the questions and info and notes etc on putting this together.

As a reminder, here is a link to the current information in the files section:
https://groups.io/g/TekScopes/files/Tek%20TM500%20Power%20Module%20Tester%20067-1201-99%20New%20Ver.
Photos of my completed unit will be added soon, and further info and updates added as required so check back often.

Link to the Digikey shopping cart:
https://www.digikey.com/short/47b1wq

And a couple videos I made on the construction and use of the Mainframe Tester:
Construction: https://youtu.be/Afwqtc6Fxd4
Use: https://youtu.be/vXd10kKFFGw

First up, there was a minor miscommunication with the PCB fab house and a chamfer on the card edge connector was accidentally omitted.
This is easy to create with a few even strokes with a flat file in the direction AWAY from the fingers (don't file towards the board, only away or you run the risk of tearing the fingers) ensure you run the file the entire width of the edge connector from one side to the other for each stroke to keep the chamfer even, don't make small.strokes along the width.
It shouldn't take much more than 5 strokes per side or so, you shouldn't need much more than 0.25mm of chamfer or so.
Some may note that this will leave a tiny sliver of exposed copper along the edge. This was unavoidable even if the PCB fab were to do the chamfer as the machining is done after plating.
To seal the edge if desired, some Deoxit Gold can be applied (also to the areas where the keying slots are milled into the fingers) or placing some masking tape to cover the gold fingers to the exposed edge then spraying a little circuitboard laquer or similar along the end edge of the PCB.

Besides that, it should go together pretty easily.
Feel free to ask questions and suggest additions and corrections to the manual I wrote etc.


Andy Warner
 

So far, I have one observation, and one question:
1. observation - digikey BOM has a typo in the reference designators for the 1N4007 diodes. "CR11" should read "CR101".
2. question - if I insert the stops in S3 where the manual suggests on page 2, the index on the knob does not align with the front panel when using the flat on the shaft with the grub screw.
I plan on buzzing the switch out to see what the correct location is, but I thought I would ping the list about the inconsistency as well.

--
Andy


Dave Seiter
 

I ran across number 2 also, but the knob I decided to use had two set screws, so I tightened the one on the round portion first, then the one on the flat section.  It's not bullet proof, but it will work. 
-Dave

On Saturday, February 20, 2021, 11:13:34 AM PST, Andy Warner <andyw@pobox.com> wrote:

So far, I have one observation, and one question:
1. observation - digikey BOM has a typo in the reference designators for the 1N4007 diodes. "CR11" should read "CR101".
2. question - if I insert the stops in S3 where the manual suggests on page 2, the index on the knob does not align with the front panel when using the flat on the shaft with the grub screw.
              I plan on buzzing the switch out to see what the correct location is, but I thought I would ping the list about the inconsistency as well.

--
Andy


Dave Seiter
 

I finished my unit and then discovered that the +15V didn't work.  Took about 2 minutes of head scratching before I realized I hadn't soldered the connections for that binding post, the scope output and one of the phase LEDs....


Jared Cabot
 

The mistake with the diode designation was fixed in a later revision of the manual. If you download the latest, it'll have all the problems fixed that are found to date.

As for the knob, mine doesn't line up with the flat either, its just a function of the position of the number markings on the front panel that I copied directly from the Tek design. I would have preferred to use a round shaft switch but only flat was available outside of a custom order, so just ignore the flat and align the knob to the numbering.
I might put a note about that in the manual too (It's these small details that slip my mind when I am writing the manual after building the unit, so keep them coming so I can make the manual as accurate and detailed as possible! :) )

As of now with the addition of information about the knob position, the manual is at Version 1.6


Andy Warner
 

I was reporting the diode designator was incorrect in the "customer reference" field of the DigiKey BOM (which gets printed on the component bags), not in the manual.

Minor typos/copy-pasta in manual:
- Step IV - PNP Short/Leakage (Page 7) - The first sentence of the procedure references an NPN transistor instead of a PNP.
-Second sentence: "meter reading drifts down to zero" should read "meter reading drifts up towards zero"