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Test Equipment Anonymous (TEA) group therapy thread

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--- Quote from: factory on December 07, 2023, 07:51:48 pm ---
--- Quote from: PA0PBZ on December 07, 2023, 10:12:30 am ---
--- Quote ---The frequency source used for preliminary experiments was a Fluke 633A-01 Synthesizer. Although any source with good long term and short term frequency stability characteristics could be used, a synthesizer provides the operator with a readily selectable frequency source. The 633A-01 has a range of 0 to 11 mHz with frequency selection at 0. 1 Hz increments. The internal standard has a stability of better than 2 parts per 109 per day.

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So frequency generating after all? But why would a synthesizer have those voltage references?  :-//

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A programmable VCO wouldt need references to compare against?

The pictured from Wireless World March 1969 one might be the 644A, which had two boxes in another picture on the web.


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I think you've found it. Wow, so buried is this model and the related 622A and 644A. From that information, I found a photo of the 644A in a rack (with a smaller box on top of course). So it appears I'm simply missing the other box. Would be cool to have, seems pretty neat. "Search" seems to be basically "sweep", which makes sense. For now, I will just enjoy the voltage reference feature.

Despite the very fine resistors inside it, I am always hesitant to rely on anything with potentiometers inside it. But we will see. My LM399-in-a-can project is coming along and soon I will have some sense of calibration about my lab-shanty. Next, I cal the Fluke 8505A and HP 3490A, and then this 633A.

TERRA Operative:
Just got myself a 'not working' Tek TDS640A scope, yet another one of these things..... :-DD Couldn't say no for 5000yen.

It has a smashed front glass window over the CRT (that saved the CRT through its self sacrifice) so I'll need to find one of those, not sure if I have a spare..
I ripped it apart last night and am now finishing up cleaning it out, it must be from a heavy machinery or vehicle workshop, as it was coated inside and out in a film of diesel oil.... blegh. Not as bad as the nicotine hazmat one I had a while back but still gross..

The PSU is verified working with my tester so far, so I'm wondering if the fault is something deeper, or if the seller just forgot to flick the master power switch on at the back. :D

I'll have it all back together this weekend, so I'll be able to see what's up soon.

Well, I won the TEA lottery again. I fished out from the dumpster a fully functional HP boatanchor impedance meter, along with a Keithley 4 quadrant supply (which I thought was off by 1V, but it turned out that the person before me forgot to connect the sense wires) and two generic lab bench power supplies. I also fished out a 35kV power supply with no current limiting, except for the input mains fuse. That one has a broken panel meter, and I’ll investigate later.

Anyways it’s time for VCA (Vintage Computer Anonymous). I also got an IBM 5155 from the same dumpster which didn’t post. Thanks to the kind people at minuszerodegrees, I was able to identify the problem. The CPU clock was running at 20 MHz, way faster than the 4.77 MHz it was designed for. The 14.31818MHz crystal was running at about 60 MHz. An autopsy revealed that the crystal had cracked. I swapped it with a 16MHz crystal and the computer booted. Unfortunately, the display timing is derived from this crystal, so I need an exact replacement. Without it, a lot of gibberish is displayed.

I'll swap it sometime soon and we'll see if it works.

Just for completeness I also put a few pictures of my TE score. I accidentally dropped the Keithley from dumpster height (never trust old handles), but the only thing that broke was the power switch. My replacement is pretty sacrilegious, so I'll just consider it a temporary solution. The 35kV supply seems to have a dead high voltage resistor.


--- Quote from: tggzzz on November 28, 2023, 11:26:51 am ---
--- Quote from: TERRA Operative on November 28, 2023, 12:49:10 am ---I rebuilt my [THS7xx] batteries with tabbed Ni-MH C cells.
I carefully pulled the ring and strap off the old pack for the side contact after cutting the black heatshrink away.
I then soldered together the 4 C cells and taped them solid with kapton tape. After adding more kapton tape to where the contact ring sits for a gently firm fit, the ring and strap were soldered to the battery too.
After that I just covered in some new black battery pack heat shrink from ebay and then applied a label I made and printed out on printable sticker paper (I used thin packing tape to laminate the sticker to make it shiny and protect it).
I've made like 3 packs this way, they all worked out well with various amounts of swearing. :D

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Neat :) I like the kapton tape idea for holding them before adding the heatshrink.

My current thinking <insert timestamp here> is to leave the original battery untouched, but then make a new battery from stuff in my junkbox treasure chest:

* use my existing sub-C cells (NiCd, 2Ah, tabbed, NOS but expired 4 years ago) which look like being the right diameter but a few mm short
* hopefully just bend the existing three tabs between 4 cells through 180degrees, so the cells are above each other rather than next to each other
* use some sheet phosphor to create the ring contact and "wire" to the top end
* use insulating spacers and/or metal washers to extend the battery to the correct length
* cover the lot in heatshrinkThere are a few details that I'll work out as I go.

It will then be perfectly obvious that this is an, ahem, aftermarket battery, and can be compared with the original.

That's what I've done when remaking Tek1502 batteries, which are a pain by comparison (always leaking, sometimes the battery box is broken).

--- Quote ---tggzzz, if you let me know the capacity of your final battery, chemistry and month/year of construction, I can spit out some labels in a PDF file for you to print your own labels if you like. :)

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Thanks, but I'll just put a handwritten paper label on it.

--- Quote ---For those resistors, if you install all of them, you'll get a THS710A. Not sure why you'd want the downgrade though. :D

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Oh.... pffffft. That's what happens when I don't read things correctly before replying.

I'm not too worried about removing SMD resistors; I had to do that on a Tek 2445A where the electrolytic had wreaked its traditional havoc.

--- Quote ---Also, while you can tell your scope it is a THS730A with the resistors (removing both R204 and R205), you won't get the increased bandwidth without finding some replacement input hybrids and a few other bits, in which case you'll be pulling parts from a THS730A anyway, so the point is moot... :)

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Yeah, that would be a step too far, and I have other scopes with better bandwidth (Tek 485, Philips PM3400).

--- Quote ---I have found the details of the official process for upgrading the firmware that needs no desoldering or adjustment and uploaded to Tekwiki, but it needs an obsolete and practically unobtanium dev board... (a Motorola M68332BCCDI 'DIBUG' debug module) The Tek motherboard for the programming pod is otherwise pretty simple to construct, if it weren't for that apparently rare dev board.
I think maybe it could all be emulated or reverse engineered to a raspberry pi, except I have no experience with such software things, and all my THS scopes are updated anyway... so.... meh?

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Sounds like too much trouble for too little benefit.

It has the 1.14 firmware, and has apparently only been powered up 480 times. Until I find otherwise, that will be sufficient.

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So I finally got around to making a battery pack, pretty much as I described above. Here it is with the original alongside.

The red part is thin heatshrink, and the general diameter is slightly less than the original's. That means any slight bend in the battery is less likely to cause it to jam.
The white part under the transparent heatshrink on the left is simply a plastic spacer; the dimensions aren't critical since the battery contact on the right hand side is the traditional long-travel spring.
The only important dimensions are

* the diameter of the brass ring contact, since the corresponding contact is only short-travel
* the distance of the brass ring contact from the right hand end; not difficult to get right
Can't be bothered to upgrade it by removing SMD resistors, nor to upgrade the firmware.

Don't have the connecting cable, but I'll build one if I ever need it.

Thanks for all your suggestions :)

TERRA Operative:
What cells did you use? They don't look like C size. Sub-C?


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