Re: Unusual TM5xx(x) MF - its not a TM500 or a TM5000


Hi Bob,
It would be very misleading if these unusual hybrids were referred to as TM502A, TM503A, etc.
There is a TM502A (I have two) and it is nothing but an updated version of a TM502. It is clearly marked at the front as a TM502A. There are no special wirings of either slot that would prevent any TM500 plugin from working properly. There is no additional barrier that would prevent any TM500 plugin from being used in either slot.
I don't have a TM503A (if one exists) so I can't say how that differs from a TM503 but it would have to have three fully functional slots and no additional barriers or a rewired pass transistor dedicated as a regulated power supply for the middle slot.
This unusual three wide mainframe I am describing has NO MARKINGS on it to indicate what it is. Apparently Tek avoided the question entirely of what exactly it is by not saying anything at all. I do have an AM503 that came from an AM503S stand-alone instrument that I described in my previous email. It is just an ordinary AM503 but it has THREE labels on it. The first label, which is in the usual place, is the original serial number it was given: B086364. The next label says IDENTIFICATION and it lists this plugin as AM503S. The last label is another serial number (presumably for the entire stand-alone AM 503S instrument package and it is: B013019.
Dennis Tillman W7PF

-----Original Message-----
From: bobh@...
Sent: Tuesday, April 09, 2019 5:06 AM
Subject: Re: [TekScopes] Unusual TM5xx(x) MF - its not a TM500 or a

Aren't these referred to as TM502A, TM503A, etc? I have a TM503A and
it also does not have a fan of course since it doesn't have the space
in the bottom, as you mentioned, for air flow.


On 4/9/2019 12:08 AM, Dennis Tillman W7PF wrote:
For several years I have been aware that there are some unusual TM
5xx(x) Main Frame power supplies floating around that look, at first
glance like a newer model TM502 or TM503 but they have GPIB
in them which only a TM5003 or TM5006 would have. In addition there
another distinguishing feature to help spot that this is not a
a TM5003 has a 1" high plenum with a grille on the front of the MF
under the three slots. This MF does not have a plenum.

The three wide MF has an additional barrier strip in the center
connector to prevent a common TM500 plugin from being inserted in
The other slot(s) will accept regular TM500 plugins. I have two of
these unusual 3 wide MFs.
An easy way to distinguish them is the unusual adjustable handle
lets you position the MF in many different positions on a desk.

These MFs were introduced by Tek to allow some of their GPIB
TM5000 plugins to be operated as stand-alone instruments. Ones that
am aware of

AFG 5501 (AFG 5101 in a three wide MF)
AM 503S (AM 503 and 016-0362-02 Tool Box in a two wide MF),
also known as AM 5030
DM 5520 (DM 5120 in a three wide MF)
PFG 5505 (PFG 5105 in a three wide MF)
There may be more.

I finally got around to opening one of these 3 wide units up and I
very surprised at what I saw. It is extremely sparse. It appears the
Tek engineers have reduced this design down to a bare minimum number
of parts.
There is a transformer (not an SMPS) and a backplane, a few wires
connectors, 6 pass transistors and little else.

The backplane has a part number on it and I am hoping someone can
supply a schematic for it although I don't think it is too much
different from a TM503. The backplane is marked RA-9804-00 POWER
SUPPLY (C) 1988.

There are three filter capacitors on the backplane 22,000uF/16V,
4,700uF/50V, and 4,700uF/50V. The backplane has three TM503
and three GPIB connectors and two pass transistors for each slot.

I couldn't measure the pass transistors to confirm there is a PNP
an NPN for each slot but that is a safe assumption. One of the pass
transistors for the middle slot appears to be connected to a 9V
Diode which appears to force it to be a simple 10V regulator. That
probably why there is a barrier strip in the middle slot between
positions 27 and 28. I did not see any reason the back plane
be modified to remove the simple regulator and rewire the pass
transistor to be like any other TM503.
Dennis Tillman W7PF
Dennis Tillman W7PF
TekScopes Moderator

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