Tektronix 556 Fan Motor Repair Part 1
I was recently fortunate enough to acquire a Tektronix 556 Dual Beam Oscilloscope with many accessories and in good condition. Unfortunately, the cooling fan on the scope was very loud and more concerning, it emitted an alarming metal on metal contact sound. After verifying basic operation of the oscilloscope, I decided to repair the cooling fan. This process is documented in the images and commentary that follow.
Part 1: Removing the Noisy Fan Motor
556 Cooling Module with filter and mesh screen removed. The fan is connected to the chassis wiring at the ceramic terminal which is circled:
Fan to chassis wiring connection terminal.
Inside of cooling module and bottom side of motor (fan blade removed):
Back side of motor (fan blade removed). This is a 4 pole 1725 rpm (loaded) motor. It moves a very large volume of air.
An … Read More »
Tektronix Scope-Mobile Cart Repair Part 2
This post continues my repair of the Tektronix Scope-Mobile Cart and trunnion mounts. Here is Part 1, which details the problem and my proposed solution.
The original design used 5/16″ button head bolts which screwed into the bosses and attached the aluminum box frame member to the polymer trunnion mount:
It is obvious that overtightening these bolts put the bosses into tension which caused them to fail. The gap between the member and the boss “spring loads” the system and puts additional tensile stress on the boss. While an aluminum casting could easily handle these stresses, the polymer obviously could not.
What I did was to glue the fractured bosses into place using a low surface energy epoxy and use them as a drilling guide (see Part 1). Then I drilled completely through the trunnion mounts with a drill press, using … Read More »
Tektronix Scope-Mobile Cart Repair Part 1
I was lucky enough to obtain a Tektronix 202-2 Scope-Mobile Cart.
Upon examining it, I found that the scope tray was loose and the tilt mechanism did not function properly. The cause for this was broken trunnion mounts on both sides of the cart as follows:
Three of the four bosses were fractured with the fracture surface indicating tensile overload. I suspect that the bolts were overtightened and the bosses fractured. Overtightening loaded the bosses in tension by trying to compress the box frame member. Unfortunately this type of polymer (some type of hard thermoplastic) is not good in tension.
Other mobile carts I have seen use cast aluminum for these trunnion mounts, which is a better choice for strength and durability. The cart I have for my 556, a 205-2 (triple wide), uses cast aluminum trunnion mounts.
I … Read More »
Tektronix 556 Dual Beam Oscilloscope Images
What follows is a series of images of my Tektronix 556 Dual Beam Oscilloscope displaying various waveforms. I am learning about this scope and how to use it.
A brief description of the unit can be found here: Tektronix 556
Thanks for reading.
Tektronix 556 Dual Beam Oscilloscope
I had recently the unique opportunity to acquire a complete Tektronix 556 Oscilloscope setup. This comprised the oscilloscope itself, the matching scope cart, original manual, probes and 12 plug-in units. This in itself is rare enough, but in addition, this particular scope has the optically desirable blue phosphor CRT and Tektronix C-27 Camera Bezel. This 50 MHz bandwidth oscilloscope was the state of the art when it was introduced in the mid 1960’s: Tekwiki Tek 556
This will be the first of many posts and updates as I work my way through checking and restoring this beautiful scope.
And now some images:
Tektronix Oscilloscopes 7904, 2467B, 2465B at 1GHz
The images to follow show a 1 GHz sine wave (amplitude not changed during the testing) on the following Tektronix oscilloscopes:
Tektronix 7904 with 7A24 vertical (400 MHz) and 7B92A horizontal
Tektronix 2467B (400 MHz scope)
Tektronix 2465B (400 MHz scope)
I have checked the bandwidth of the both the 2465B and 2467B used here, and they meet the 400MHz requirement at -3db (using a Tektronix SG504 with leveling head). The bandwidth of the 7904 mainframe + 7A24 vertical plug-in used in this test is about 450 MHz (-3db), but it remains at almost that level out to > 600 MHz. At 1 GHz I can still easily get 175 mV of signal on the screen of the 7904 + 7A24 where the two newer scopes can only manage 25 mV or less.
Tektronix 7904 Oscilloscope
Here are some images of one 7904 mainframe with a 7A24 vertical module and a 7B92A horizontal module. The scope screen shows the pulse from an S52 pulse head; the rise time is about 850ps which translates into a bandwidth of about 412 MHz. Since the 7A24 plug-in is specified at 400 MHz, this is about right.
This is the same pulse from an S52 pulse head but using an S4 sampling head instead of the 7A24 vertical amplifier
Tektronix 7000 Series Equipment
I am doing some testing on recently acquired Tektronix 7000 series equipment. Involved in these images is a Tektronix 7904A mainframe using a 7S12 TDR/Sampler plug in with an S52 pulse generator and S4 sampling head.
The rise time on of the pulse is about 32ps which translates to a bandwidth of about 11 GHz; all this for a few hundred dollars.