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TM500 extender redux.


Andy Warner
 

I've uploaded an album showing a TM500 extender with self-contained pass
transistors that I just built.

It is based on the ~$10 JAMMA extenders that you can buy on ebay or amazon,
plus a handful of parts from Digikey. I bought a new EDAC edge connector,
but you could just as easily re-use the JAMMA edge connector, if you wished.

I know the hFE of the pass transistors is low (>= 20), but I have seen them
oscillate using a JAMMA extender. Maybe this is because of the thin wires
used by the JAMMA extenders, maybe it is because a module is marginal
(which may be why I have it on an extender in the first place), perhaps it
only happens when both conditions apply.

The idea of using pass transistors mounted at the edge connector is based
on Phillipe's work here : http://philippe.demerliac.free.fr/Tek.htm

The heatsink gets warm to hot (35-40C) in normal module usage, not
dangerous - you could certainly use a larger heatsink, if you wished. I
probably would not run a PS503A @ 1A on all outputs for very long, using
this extender.

Photo album, with part numbers and construction guidance in the comments
here: https://groups.io/g/TekScopes/album?id=252147

I did not replace all the JAMMA wires with heavier gauge, it seems to work
well enough for my immediate needs without this.

Hope others might find this useful,
--
Andy


Stephen
 

Very nice job Andy.
Thank you for sharing.

I read the description on his site too. That guy did a very, very nice job!!! Impressive!!
I wished I had the proper tools and the space to make enclosure from scratch like this.


Ke-Fong Lin
 

Hi Andy,

What pass transistors did you use?
I've used TIP35C and TIP36C, along with 22 AWG wires.
Never had an "oscillation" problem, even with all the wires "bundled" together with cable ties.

https://groups.io/g/TekScopes/album?id=243643
https://github.com/anotherlin/tek_tm_ext


Best regards,


Andy Warner
 

I used MJF2955 and MJF3055 transistors.

On Sun, Aug 16, 2020 at 2:38 PM Ke-Fong Lin <anotherlin@...> wrote:

Hi Andy,

What pass transistors did you use?
I've used TIP35C and TIP36C, along with 22 AWG wires.
Never had an "oscillation" problem, even with all the wires "bundled"
together with cable ties.

https://groups.io/g/TekScopes/album?id=243643
https://github.com/anotherlin/tek_tm_ext


Best regards,



--
Andy


Stephen
 

Excuse me for asking, but does that mean that there are now 4 pass transistors when this is hooked up??


Andy Warner
 

No, that would make no sense.

The transistors in the chassis are not used.

The only ones connected to the module under test are the two on the
heatsink right next to the module.

On Sun, Aug 16, 2020 at 3:01 PM Stephen <stephen.nabet@...> wrote:

Excuse me for asking, but does that mean that there are now 4 pass
transistors when this is hooked up??



--
Andy


Stephen
 

On Sun, Aug 16, 2020 at 09:10 AM, Andy Warner wrote:


No, that would make no sense.

The transistors in the chassis are not used.

The only ones connected to the module under test are the two on the
heatsink right next to the module.
That’s what I thought. But how do you manage to bypass them?