Topics

TM500 Plug-in Extention


Stephen
 

I’ve finally found the time to make an extender using JAMMA connectors to be able to troubleshoot my DC 503 and my SC 502

I’ve removed the bridge connections from 1-2 and 3-4, and wired all the pins from 1-5 and 7-13.
Pretty straight forward process. I didn’t connect anything beyond pin 13. Pins 2-3-4-8-12 use only one wire As both sides are connected.

I’ve tried PS503 and it works fine, except that when inside the TM, I can check the +/- 20VDC AND the +5VDC while my ground lead is connected to either ones on the plugin. But not when connected via the extender.

However, no other plugin (AM502, DC503, FG503) is working besides the PS503...
I’ve checked the voltages, and everything is exactly the same on the extender as on the TM506 connector itself.
There’s also full continuity between both ands of the extender.

I understand that pin 14 to 28 are not used when it comes to just power the plugins...

What am I doing wrong??


Andy Warner
 

A problem I have seen with both home brew and official Tek extenders is
that the pass transistors can oscillate. Since they are most often used for
regulated supplies, it tends to make the entire module under test misbehave
badly. I seem to remember reading somewhere that the linear regulator
circuits these transistors are used in are sometimes near the edge of the
working envelope. Adding 60cm of wire to each transistor lead can just tip
them over the edge.

After seeing this: http://philippe.demerliac.free.fr/Tek.htm,
I am planning to modify one of my jamma-based extenders to add pass
transistors and heatsink mounted right at the module connector, to see if
it improves things.
Will report back when I have some results to share with the list.

Others have mentioned using ferrite beads to tamp down the oscillations, I
think mostly in the context of when you replace the transistors in the
mainframe; but perhaps it would help on the long leads. I doubt it can hurt.

On Mon, Aug 10, 2020 at 06:56 Stephen <stephen.nabet@...> wrote:

I’ve finally found the time to make an extender using JAMMA connectors to
be able to troubleshoot my DC 503 and my SC 502

I’ve removed the bridge connections from 1-2 and 3-4, and wired all the
pins from 1-5 and 7-13.
Pretty straight forward process. I didn’t connect anything beyond pin
13. Pins 2-3-4-8-12 use only one wire As both sides are connected.

I’ve tried PS503 and it works fine, except that when inside the TM, I can
check the +/- 20VDC AND the +5VDC while my ground lead is connected to
either ones on the plugin. But not when connected via the extender.

However, no other plugin (AM502, DC503, FG503) is working besides the
PS503...
I’ve checked the voltages, and everything is exactly the same on the
extender as on the TM506 connector itself.
There’s also full continuity between both ands of the extender.

I understand that pin 14 to 28 are not used when it comes to just power
the plugins...

What am I doing wrong??



--
Andy


Stephen
 

On Mon, Aug 10, 2020 at 02:03 AM, Andy Warner wrote:


A problem I have seen with both home brew and official Tek extenders is
that the pass transistors can oscillate. Since they are most often used for
regulated supplies, it tends to make the entire module under test misbehave
badly. I seem to remember reading somewhere that the linear regulator
circuits these transistors are used in are sometimes near the edge of the
working envelope. Adding 60cm of wire to each transistor lead can just tip
them over the edge.

After seeing this: http://philippe.demerliac.free.fr/Tek.htm,
I am planning to modify one of my jamma-based extenders to add pass
transistors and heatsink mounted right at the module connector, to see if
it improves things.
Will report back when I have some results to share with the list.

Others have mentioned using ferrite beads to tamp down the oscillations, I
think mostly in the context of when you replace the transistors in the
mainframe; but perhaps it would help on the long leads. I doubt it can hurt.
Interesting...
I think I have some larger beads laying around. I’m gonna put one on each end of the connector and see if it helps.
Will report back.

Thank you for the info Andy.


Stephen
 

Putting one small bead didn’t help...


Colin Herbert
 

My TM 500 extenders were supplied as a kit from Dan Meeks (though I doubt he has any left) and the ribbon-cable is ~87 cm long. I can't say that I've seen any problems with oscillation of the pass-transistors in the mainframe, but wouldn't they need to be connected to some circuitry in a plug-in at the other end of the extender? I can't see how an unpowered transistor can oscillate.
Colin.

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Stephen
Sent: 10 August 2020 15:28
To: TekScopes@groups.io
Subject: Re: [TekScopes] TM500 Plug-in Extention

Putting one small bead didn’t help...


Harvey White
 

What was pin 6 connected to?

Harvey

On 8/10/2020 10:43 AM, Colin Herbert via groups.io wrote:
My TM 500 extenders were supplied as a kit from Dan Meeks (though I doubt he has any left) and the ribbon-cable is ~87 cm long. I can't say that I've seen any problems with oscillation of the pass-transistors in the mainframe, but wouldn't they need to be connected to some circuitry in a plug-in at the other end of the extender? I can't see how an unpowered transistor can oscillate.
Colin.

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Stephen
Sent: 10 August 2020 15:28
To: TekScopes@groups.io
Subject: Re: [TekScopes] TM500 Plug-in Extention

Putting one small bead didn’t help...







Stephen
 

On Mon, Aug 10, 2020 at 03:43 AM, Colin Herbert wrote:


My TM 500 extenders were supplied as a kit from Dan Meeks (though I doubt he
has any left) and the ribbon-cable is ~87 cm long. I can't say that I've seen
any problems with oscillation of the pass-transistors in the mainframe, but
wouldn't they need to be connected to some circuitry in a plug-in at the other
end of the extender? I can't see how an unpowered transistor can oscillate.
Colin.
My cable measures ~57cm. Probably I didn’t understand you correctly, but the extender is connected
to the circuit of the plugin itself??


Colin Herbert
 

I assume you mean connector 6B on the backplane. It doesn't connect to anything, but there is a plug-in equivalent board which takes a header to a 60-way ribbon cable. I haven't investigated which wires go to which backplane connectors, as I don't really need to know, so long as the thing works. I have checked that 6A connects to 6A (base of the NPN series pass transistor)and 6B connects to 6B (even though there is no connection on the backplane). Since the ribbon cable is 60-way but there are only 56 connectors on the backplane, there must be four redundant wires in the ribbon cable. I have no idea which ones they are, nor do I need to know, I think. It is maybe a pity that I can't show a photo of the extender, which might make the arrangements clearer.
Colin

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Harvey White
Sent: 10 August 2020 17:16
To: TekScopes@groups.io
Subject: Re: [TekScopes] TM500 Plug-in Extention

What was pin 6 connected to?

Harvey


On 8/10/2020 10:43 AM, Colin Herbert via groups.io wrote:
My TM 500 extenders were supplied as a kit from Dan Meeks (though I doubt he has any left) and the ribbon-cable is ~87 cm long. I can't say that I've seen any problems with oscillation of the pass-transistors in the mainframe, but wouldn't they need to be connected to some circuitry in a plug-in at the other end of the extender? I can't see how an unpowered transistor can oscillate.
Colin.

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Stephen
Sent: 10 August 2020 15:28
To: TekScopes@groups.io
Subject: Re: [TekScopes] TM500 Plug-in Extention

Putting one small bead didn’t help...








Stephen
 

On Mon, Aug 10, 2020 at 05:16 AM, Harvey White wrote:


What was pin 6 connected to?

Harvey
Nothing. I left it blank


Stephen
 

I followed this instructions that I found here:

https://www.eserviceinfo.com/download.php?downloadstart=1&fileid=76289


Colin Herbert
 

I can either connect the appropriate end of the Dan Meeks extender to a plug-in or not. The extender has a number of leds to indicate the status of some of the power-lines. It doesn't need to be connected to a plug-in any more than the backplane needs to have any plug-ins plugged in. If there is nothing connected to the pass-transistors (i.e. there is no plug-in present, no extender present, nor are they otherwise electrically connected to anything, then surely they cannot oscillate?)
Colin.

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Stephen
Sent: 10 August 2020 17:28
To: TekScopes@groups.io
Subject: Re: [TekScopes] TM500 Plug-in Extention

On Mon, Aug 10, 2020 at 03:43 AM, Colin Herbert wrote:


My TM 500 extenders were supplied as a kit from Dan Meeks (though I doubt he
has any left) and the ribbon-cable is ~87 cm long. I can't say that I've seen
any problems with oscillation of the pass-transistors in the mainframe, but
wouldn't they need to be connected to some circuitry in a plug-in at the other
end of the extender? I can't see how an unpowered transistor can oscillate.
Colin.
My cable measures ~57cm. Probably I didn’t understand you correctly, but the extender is connected
to the circuit of the plugin itself??


Stephen
 

On Mon, Aug 10, 2020 at 05:56 AM, Colin Herbert wrote:


I can either connect the appropriate end of the Dan Meeks extender to a
plug-in or not. The extender has a number of leds to indicate the status of
some of the power-lines. It doesn't need to be connected to a plug-in any more
than the backplane needs to have any plug-ins plugged in. If there is nothing
connected to the pass-transistors (i.e. there is no plug-in present, no
extender present, nor are they otherwise electrically connected to anything,
then surely they cannot oscillate?)
Colin.
Yes, of course. You’re right. I misunderstood you the first time.


Stephen
 

On Mon, Aug 10, 2020 at 05:45 AM, Colin Herbert wrote:

It is maybe a pity that I can't show a photo of the extender, which might make the arrangements clearer.
Colin
I don’t know if I can explain it correctly, but what I did is pretty straight forward.
I have a wire on both sides of the male connector (the one that plugs into the chassis) connected to each side of the other end. As if they were the same unit, if you will. Only pin 2,3,4,8 and 12 are bridged together. Exactly as the instructions above suggest. 6A and 6B, as well as everything from 14 up are left blank.


Göran Krusell
 

Hi, if you have oscillations caused by very long leads to the power transistor, you mentioned 60 cm which
would have an inductance of 600nH approximately, then you can most likely solve this by soldering a
47 ohm resistor to the base pin, 1 to 3 cm off.
Also if possible the collector should be decoupled to ground with a 100nF capacitor (here I am not familiar
with your circuit diagram).

Göran


Colin Herbert
 

I will use the Tektronix nomenclature, since this is more concerned with Tektronix than with JAMMA. The numbers of the connectors go from 1 at the bottom to 28 at the top. Looking at the backplane connector from its front (the side that things plug into, rather than that where thing are soldered onto), the connectors on the left are the "A" connectors and those on the right are the "B" connectors.

A2 and B2 are both connected to +11.5 filtered DC
A3, B3, A4 and B4 are all connected to +11.5 V Common Return
8A and 8B are both connected to -33.5 v filtered DC
12A and 12B are both connected to +33.5 V filtered DC
6A is the base lead of the NPN series-pass transistor and should be included in the extender wiring.
6B has no connection
All connectors, both A and B sides from 14 upwards are not assigned, but might have connections to some plug-ins in order to interconnect them. The Manual for the plug-in will indicate anything like this.

I think that any Power Module will give pin assignments to the backplane.
Colin.

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Stephen
Sent: 10 August 2020 18:06
To: TekScopes@groups.io
Subject: Re: [TekScopes] TM500 Plug-in Extention

On Mon, Aug 10, 2020 at 05:45 AM, Colin Herbert wrote:

It is maybe a pity that I can't show a photo of the extender, which might make the arrangements clearer.
Colin
I don’t know if I can explain it correctly, but what I did is pretty straight forward.
I have a wire on both sides of the male connector (the one that plugs into the chassis) connected to each side of the other end. As if they were the same unit, if you will. Only pin 2,3,4,8 and 12 are bridged together. Exactly as the instructions above suggest. 6A and 6B, as well as everything from 14 up are left blank.


Stephen
 

I don’t know if I do have oscillation.
But if there were any, wouldn’t the PS503 not be working as well?

Where should I check for oscillation? Pin 7 and 12? Respectively “collector lead to NPN and PNP pass transistors”?


Stephen
 

Thank you Colin.

Yes, it’s better to use the Tektronix nomenclature. And after reading your post I realized that I left both the A an B sides of pin 6 disconnected whereas 6A should be.
Thank you for pointing that out.


Andy Warner
 

I was the one that raised the spectre of external pass transistors
oscillating when used by a module via an extender.

I have seen it myself on an FG504, and remember rumblings on the list about
it.

Was simply suggesting to the list in response to Stephen that in my
experience some modules can provoke this behaviour, while others do not.
I do not have a large enough sample set to determine if the issues are
per-module-design, per-physical-module, per-enclosure, or a mix of all.
However, I am planning to test a modified extender which seeks to address
this particular backwater.

I don't know where the idea of unused transistors oscillating came from,
it's not an issue.

On Mon, Aug 10, 2020 at 1:04 PM Stephen <stephen.nabet@...> wrote:

I don’t know if I do have oscillation.
But if there were any, wouldn’t the PS503 not be working as well?

Where should I check for oscillation? Pin 7 and 12? Respectively
“collector lead to NPN and PNP pass transistors”?



--
Andy


Dave Daniel
 

There’s also a TM500 interface reference manual for all of this. There’s probably a copy on TekWiki.

DaveD

On Aug 10, 2020, at 14:03, Colin Herbert via groups.io <colingherbert=blueyonder.co.uk@groups.io> wrote:

I will use the Tektronix nomenclature, since this is more concerned with Tektronix than with JAMMA. The numbers of the connectors go from 1 at the bottom to 28 at the top. Looking at the backplane connector from its front (the side that things plug into, rather than that where thing are soldered onto), the connectors on the left are the "A" connectors and those on the right are the "B" connectors.

A2 and B2 are both connected to +11.5 filtered DC
A3, B3, A4 and B4 are all connected to +11.5 V Common Return
8A and 8B are both connected to -33.5 v filtered DC
12A and 12B are both connected to +33.5 V filtered DC
6A is the base lead of the NPN series-pass transistor and should be included in the extender wiring.
6B has no connection
All connectors, both A and B sides from 14 upwards are not assigned, but might have connections to some plug-ins in order to interconnect them. The Manual for the plug-in will indicate anything like this.

I think that any Power Module will give pin assignments to the backplane.
Colin.

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Stephen
Sent: 10 August 2020 18:06
To: TekScopes@groups.io
Subject: Re: [TekScopes] TM500 Plug-in Extention

On Mon, Aug 10, 2020 at 05:45 AM, Colin Herbert wrote:

It is maybe a pity that I can't show a photo of the extender, which might make the arrangements clearer.
Colin
I don’t know if I can explain it correctly, but what I did is pretty straight forward.
I have a wire on both sides of the male connector (the one that plugs into the chassis) connected to each side of the other end. As if they were the same unit, if you will. Only pin 2,3,4,8 and 12 are bridged together. Exactly as the instructions above suggest. 6A and 6B, as well as everything from 14 up are left blank.







Stephen
 

Yes Andy, you were the one who raised that issue.

And also thank you Harvey for asking about pin 6. I should’ve understood the hint.