Hi all,

The Snooper software (originally made by Maxa, then later by Central Point Software) used to include a NuBus diagnostic card as well as a small, black, serial loopback plug for testing the serial ports.

I'm not too fussed about the card, but does anyone have one of these loopback plugs, or even a diagram of the plug's wiring? I'd like to replicate it.

I assume it's just connecting the RxD to TxD, but I'd like to be sure.

Thanks,
Bruce

I have one the Maxa Snooper NuBus cards (1.0) ... but it didn't come with the loopback plug. I wasn't even aware that such a thing existed until now. I guess I need to read the user manual a bit closer.

I've figured it out (and made a pretty diagram). I've tested this in Snooper and it passes the handshake and data tests successfully.

I hope it's of help to others.

Awesome I was just asking about this in the discord. Thanks for figuring this out!

Thanks! Bookmarked for imminent reference.

>> splorp said:

I have one the Maxa Snooper NuBus cards (1.0) ... but it didn't come with the loopback plug. I wasn't even aware that such a thing existed until now. I guess I need to read the user manual a bit closer. Click to expand...

I don't suppose you could post some nice, clear hi res pics of both sides of the NuBus card please? I'd love to reverse engineer it.

>> Branchus said:

I don't suppose you could post some nice, clear hi res pics of both sides of the NuBus card please? I'd love to reverse engineer it. Click to expand...

Let me see what I can do ... I'll dig it out tomorrow.

@Branchus Here are a couple of high resolution images of my Snooper card. Hopefully there's enough detail to make out the traces ... the colour on this thing is really dark and low contrast.

The two capacitors appear to be the same specs (see third photo).

Let me know if you need any other details.

Magnificent photos @splorp, thank you!

You're very welcome, of course.

>> Branchus said:

I've figured it out (and made a pretty diagram). I've tested this in Snooper and it passes the handshake and data tests successfully. I hope it's of help to others. View attachment 2482 Click to expand...

Hi Bruce, thanks for figuring out the loopback connections. Just wondering if this same pinout also works for your printer port? When I do this on my printer port it is happy with the handshake lines but fails on the data lines. On the modem port it work perfectly.
Thanks.

>> craig said:

Hi Bruce, thanks for figuring out the loopback connections. Just wondering if this same pinout also works for your printer port? When I do this on my printer port it is happy with the handshake lines but fails on the data lines. On the modem port it work perfectly. Thanks. Click to expand...

Hi Craig, yes it's the same for both ports. I've only tested it on a couple of computers, but it worked for both ports on both computers.

>> Branchus said:

Hi Craig, yes it's the same for both ports. I've only tested it on a couple of computers, but it worked for both ports on both computers. Click to expand...

Sorry for the delay in replying but I'm happy to say I got my printer port working. The cause of the problem was a PCB routing error on the Bolle SE/30 Reloaded PCB (Rev02) which Bolle has now fixed in the latest board files (Rev03+) on his GitHub site.

The pins involved should have been as follows:

RP3 pin 13 to UD12 pin 14
RP3 pin 14 to UD12 pin 13

...but were actually transposed.

After that was fixed (with some enamelled wire), I ran Snooper in automatic mode for a few hours and it successfully passed over 250 cycles with no failures in any sub-system. Happy days!

>> craig said:

After that was fixed (with some enamelled wire), I ran Snooper in automatic mode for a few hours and it successfully passed over 250 cycles with no failures in any sub-system. Happy days! Click to expand...

So the little tester was actually doing its job with the failed test. Excellent!

I made a serial loopback plug with a mini DIN plug I bought from Amazon and using the instructions provided by Bruce @Branchus earlier in the thread. The serial loopback plug worked great! I am troubleshooting two problematic SE/30s which have various minor problems. One failed the modem baud tests but passed the handshake (printer port tested fine), and the other, more problematic SE/30 failed at the handshake test on both ports and Snooper hung at that point. The printer and modem ports tested just fine on a series of other classic Macs. Time for more troubleshooting on both SE/30s! Of course, I welcome any suggestions from the wonderful TinkerDifferent community :)

Success! Thanks to the serial loop back plug giving me a clue, I found several broken traces around UG12 that solved the problem for the SE/30 that failed the handshake tests. I wrote about the experience in thread 'Macintosh SE Won't Boot System 7'
https://tinkerdifferent.com/threads/macintosh-se-wont-boot-system-7.792/post-5581

I plan on tackling the other SE/30 soon.

I finally got around to making these and they worked great.

I don't know if the color scheme for serial cables are standardized, but here's how mine mapped in case it might save you a few minutes when making your own.

>> Elemenoh said:

I don't know if the color scheme for serial cables are standardized , but here's how mine mapped in case it might save you a few minutes when making your own. Click to expand...

I purchased this serial cable from Amazon Japan and can confirm wires are the same color scheme as you showed. I guess that means the colors probably are standardized.



Note that only one connector on the cable had colors which matched those pin numbers. The other connector has GRN on pin5 and ORG on pin3, and pins 1 & 2 are also reversed. That has no impact in how you make the loop-back connectors though, since 3 & 5 and 1 & 2 are connected to each other.

My handmade loopback connectors ("Serial Cable" link to Amazon USA in text description) work great with Snooper 2 to confirm proper operation of the two serial ports.

[Image: 1697753111742.png] [Image: 1697753208436.png] [Image: 1697753246408.png]

Thanks, @Branchus , for having kick started this important thread!

Does anyone have any spare Serial LoopBack Cables premade?