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Loopback board resistance ?


remowilliams

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  • 12 years later...

I can probably do that later today with my 4-port board. And yes I'm pretty sure it provides a static reading to adjust the pokey. However, like many things, I think Atari used 5 - 10% tolerant resistors so they are close in value but not like Mil spec or anything. BTW...if you remove the top cover, you can still use a 4-port loop board on a 2 port unit. You just end up getting mirrored readings off ports 2 and 4 I think because I believe port 3 is what shows the actual values for port on the 2 port unit.

 

There are also red LEDs on the board so you can verify voltage on each port although on mine, port 1's LED is dimmer than the rest but I don't think that is any fault of the consoles I've tested it on and likely just an old and slightly worn out LED?

 

My main issue with the loopback boards is the fact they are a bare PCB board and especially on a 4-port, when plugged in, it can be a right bastard to remove from the system.

 

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I provided full detailed pics of the loopback along with the measured values for the resistors. Mine doesn't have any diodes on it however unless we are counting the LEDs themselves? The pics are quite large so PM for details if interested. @cbelcher already has this information.

 

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1 hour ago, cbelcher said:

Thanks - yes 249k seems to be the calibrating resistance

No problem, and when we say 249k we mean it. The resistors on mine are color banded for 249k +- 1%. The rest of the resistors are 5%. So they are pretty tight on the tolerances for these loopback boards. 

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Decided to shrink the original pics down a bit since again they were on the large size and provide these here for archiving. I'm happy to provide the higher resolution pics to anyone. Just send me a PM to request them. Again on mine I don't have any diodes installed and it is only comprised of quite a few resistors, a single 10nf ceramic cap, a 4050 IC and some LEDs to indicate the +5 power on each port is present. This also means that there isn't any ESD protection when using this so make sure if you make something similar on your own that you use proper ESD procedures to prevent damage to the controller ports. Would be nice if there was a housing for this too or a handle as pulling this thing off an actual 4 port unit is a right bear and I usually have to use another tool to slowly work it and wedge the loopback board free on a system.

 

5200_Loopbk_topSM.thumb.jpg.d02b8a9253a2284057622a0d75c1ee43.jpg

 

 

5200_Loopbk_backSM.thumb.jpg.7c8c53f1627bee5440ab874cd034c112.jpg

 

 

5200_Loopbk_component_valuesSM.thumb.jpg.549dbcb340b04f48cab80a6679d0f2cc.jpg

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Have you considered buying a set of 15-pin controller extension cables from Console 5 to make it easier to use? A few feet of cable will change resistance a little bit but not enough to affect controller calibration all that much - the POKEY Resistor inside the 5200 already has enough tolerance to affect things a lot more, especially after 38 years’ worth of surface corrosion, plus variability in the timer capacitors inside the POKEY itself.

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21 minutes ago, DrVenkman said:

Have you considered buying a set of 15-pin controller extension cables from Console 5 to make it easier to use? A few feet of cable will change resistance a little bit but not enough to affect controller calibration all that much - the POKEY Resistor inside the 5200 already has enough tolerance to affect things a lot more, especially after 38 years’ worth of surface corrosion, plus variability in the timer capacitors inside the POKEY itself.

No I actually hadn't. But are't those 10ft extension cables? But it is a good idea. Heck, I could even just cut the extensions to 1ft each and splice them back together for that matter. I do know that the 4050 causes the controller functions to cycle rapidly as I've seen it using Petes test cart where you can see the characters going crazy and it will cause the screen to switch back and forth between tests on its own. I need to get the actual 1.1 diag rom burnt to a cart so I can test it in automatic mode where you plug in the board and then power on the 5200. Currently I only use it for pokey adjustment since all other functions are more easily tested with an actual controller plugged in.

 

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The cables we (me and @MakerMatrix) bought from Console5 to re-sell with our controllers last winter were 6’. They also sell cables with the controller-ends bare to solder to custom controllers or interfaces. You could desolder the ports on your test board and solder bare ends to the cables. 

 

Anyway, if you do, I’d be curious to see it in action. :) 

Edited by DrVenkman
typos
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Nah, I would just shorten the length of the extension cables if I were to do that since I'd rather not alter this loopback board hehe. Far as I know, Best is sold out of them now or at least that is what Bradley told me when I wanted to get a spare last year to have on hand. 

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  • 8 months later...

I thought I would take a stab at drawing out a schematic based off the pictures posted by @-^CrossBow^-, as I have never seen any such schematics like I have for the 2600 and 7800 loopback plugs.  If it does exist and I couldn't find it, I just wasted 2 hours of my life.  Oh well.  There are a number of traces on the top of the PCB you can't really make out because they run under the ports.  I'm not great at drawing out schematics or using KiCad, but this seemed fairly straightforward (with the exception of the traces I can't see).

 

I've attached a first stab at this.  But it could have errors due to trying to flip back and forth, and envision pin numbers upside down.  If anyone has one of these boards and could either check out using continuity what I have (and what I don't have) listed or is brave enough to remove the ports to see what traces under them, I'd appreciate it.

5200 Loopback Sch v0.1.pdf

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Thanks to @-^CrossBow^- above I did work on a test board for the 5200 but went a different direction.

I wanted to be able to use the keypad and fire buttons - so included those.

Also included a couple of potentiometers but can switch to 249k resistors for POKEY calibration.

These would work well with the Bohoki adapter and the Wico sticks to replace an original controller as well, I think.

 

 

5200test.jpg

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That's pretty nice. Basically a fully functional controller that you can switch static resistors in circuit to test. Although trying to play a game using those pots would be interesting to say the least. 

 

I'd still like to at least properly document the oem loop back though if possible, even if I never get around to building one. But it will at a minimum require someone with one to take the time to trace out the 17 or so unknown traces that you can't see where they end. I just guessed at them based off what little bit of the trace you can see. So they are most likely wrong. Maybe with a better understanding (than I have) of how the circuit most likely works, some better educated guesses could be made. And also hopefully they could double check the ones I could see and documented are correct.

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3 minutes ago, nick3092 said:

That's pretty nice. Basically a fully functional controller that you can switch static resistors in circuit to test. Although trying to play a game using those pots would be interesting to say the least. 

 

I'd still like to at least properly document the oem loop back though if possible, even if I never get around to building one. But it will at a minimum require someone with one to take the time to trace out the 17 or so unknown traces that you can't see where they end. I just guessed at them based off what little bit of the trace you can see. So they are most likely wrong. Maybe with a better understanding (than I have) of how the circuit most likely works, some better educated guesses could be made. And also hopefully they could double check the ones I could see and documented are correct.

 

I have both loop back boards, NOS.  Was going to sell them as a whole diagnostic kit, with manual and cart, but I can't find the cart.

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1 hour ago, CPUWIZ said:

 

I have both loop back boards, NOS.  Was going to sell them as a whole diagnostic kit, with manual and cart, but I can't find the cart.

Depending on price, I'd be interested in buying what you have without the cart. That way I could properly document this. 

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6 hours ago, -^CrossBow^- said:

I have my loopback handy, I will try and ping out what goes to what from the controller plugs so that I don't have to de-solder them from the board. Give me a few days though...

 

Thanks a lot for that.  I'd still be interested in purchasing a set, if @CPUWIZ is still looking to sell.

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As originally mentioned, I'm willing to buy the whole set of 4 and 2 port boards. And I will gladly reverse engineer and publish the results for the community, for both the 4 and 2 port boards. I have no problem if needed to desolder the jacks of boards I own to make sure they can be reproduced going forward.

 

And I'd be lying if I didn't want to add the boards to my collection. But I'm also willing to sacrifice them (although I have the proper tools to desolder them so it shouldn't be an issue) to make sure the info is published for others.

Edited by nick3092
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