IIGS ADB port isn't working?

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IIGS ADB port isn't working?

Hi all! I posted about this a while ago, but never ended up recieving any help.Basically, my apple desktop bus port has stopped working out of nowhere and I'm not remotely sure what could be causing it.I'm almost certain that isn't my keyboard, mouse, or cable that's causing the issue, as the keyboard's internals are in near perfect conditon, no corrosion, as well as the mouse, which I have tried plugging directly into the ADB port, rather than passing it through the keyboard. I've tested the continuity of the cable, it passes through just fine. The port itself seems to be in good condition, I tested the continuity as well. I'm totally clueless as to what it could be, anything helps!I want to say that it isn't even the ADB port causing it, maybe some sort of software lock? I'm really not sure.

 

Here is a photo of the front of the board, there is no corrosion as you can see.

And here is the back of the board. Please don't mind the red jumper wire, it's for the clock battery, it was added after the issue started, a solder pad had falled off the battery connection point after swapping the battery holder. 

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What diagnostic tools do you have?

A problem like this will require detailed analysis to fix. First of all, can you verify that your keyboard and mouse were working with a IIgs before the problem started? What is the model of the keyboard, is it the original "Apple Desktop Bus Keyboard" 658-4081 or A9M0330; or a newer model?

Checking the EMI filter was a good idea, I get the impression these aren't as reliable as you would hope. The pins to check for continuity are in opposed pairs: pin 1 to 8, 2 to 7, and 3 to 6. There should also be no continuity between pins of different pairs.

Can you test to see if power/ground is getting to the ADB socket when the machine is on? +5V goes on pin 2 of the socket, while ground goes on pin 3. Be careful not to short out pins with the probe, I would suggest using a short stiff wire inserted (one at a time) in the socket as a probe point. Alternatively you should be able to test this without power applied, by testing for continuity between the ADB pins and the corresponding pins on the power header J22. Its pin 4 is +5V, and its pins 1&2 are ground (pin 3 is the missing key to ensure the plug doesn't get reversed).

The board is laid out so that ADB data gets routed across nearly the whole board, from the components under the filter L2 to the KBD micro UG12. That means there are many opportunities for the trace to be damaged. Based on the schematic, there should be continuity between L2-8 and UG12-13, and between R108 (on the bottom, under L2) and UG12-29.

Based on what you have said, it sounds like a hardware problem. There is no software required for the ADB keyboard to work, the KBD micro and KBD GLU interface directly to hardware registers and provide the appearance of a traditional Apple ][ keyboard.

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Thanks for the incredibly detailed response!

Thank you for the incredibly detailed response! It's late at night where I am, but I'll respond to what I have tested at the moment, I'll go through and test the rest in the morning.

 

"What diagnostic tools do you have?"

I've got a digital multimeter and patience! 

 

"Apple Desktop Bus Keyboard" 658-4081 or A9M0330; or a newer model?"

It is a A9M0330, and yes, it was working before this issue started.

"Checking the EMI filter was a good idea, I get the impression these aren't as reliable as you would hope."

I have checked the filter's continuity, both pairs have continuity as they should.  

"Can you test to see if power/ground is getting to the ADB socket when the machine is on?"

I have tested the power and ground, power is certainly getting through both the ADB cable and socket (I think I accidentally shorted something, I'm praying I didn't do serious damage) 

"Its pin 4 is +5V, and its pins 1&2 are ground (pin 3 is the missing key to ensure the plug doesn't get reversed)."

I have been looking for info on the pinout of this power supply since I got this computer, thank you..

 

I will test the continuity of the L2-8, UG12-13 and R108 in the morning, thank you so much for the help so far!

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Apologies

Sorry, I let an error creep in to the previous post (shows the trouble with reading schematics late at night).

The points to check for the ADB data traces are not as I wrote earlier.

What you want to check are points L2-8 to UG12-13 and UG12-47, and the node between R108 and R150, and UG12-41.

I've highlighted these nets as red and yellow, respectively. The pins on UG12 are numbered counter-clockwise starting at the white dot.

By reading your other topic, I noticed something about a fuse. There are no fuses on the IIgs board, of course. There may be one in the keyboard, but I'm not sure. You do need to be careful with probing male connectors since the probe always slips. One way I've dealt with that problem in the past is to use a box of loose D-sub pins as "test points". You can slip a female D-sub pin over the male pin of the connector and it gives you an easily accessible spot to clip the DMM (or scope) probe to, using the clip accessories that come with most quality probes.

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Another trick to measuring on male connectors...

My trick I picked up from a YouTube channel many many moons ago is to simply get either some spare insulation or shrinkwrap that's slightly larger than the pins you're probing, cut it to the length of the pins, then drop it over the pins. You can then measure by sliding your probe into the tube where it will only contact the pin you're trying to probe. Even if you slip, the other pins are also covered, so your chances of a short are very low.

I use it on pins as small as the mini DIN connectors that ADB uses and it works well.

 

Cheers!

 

Chesh.

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My initial suspicion is that

My initial suspicion is that someone plugged in an ADB device while the system was powered on and damaged an ASIC. ADB is not hot-swap legal, and connecting any ADB device while the system is on risks damaging components. If you cannot get ADB working you can always put that PCB in a //e case and install the header for the //e keyboard, although you will need a standard //e mouse card, and the revised backplate.

 

I have sort of given up working on //gs boards, as too many issues come down to ASICs that cannot be sourced. 

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The ROM3 (1MB fast memory)

The ROM3 (1MB fast memory) board does not have the Apple IIe keyboard/numpad connectors of the earlier model. It isn't just the headers being left out, there are no pads routed for them on the board. I don't even think you can bodge one on to the KBD microcontroller:  it has a different model number, M50740 vs M50741, and some of the pins have been re-used for different purposes. On the ROM1 M50740, pin 38 is connected to KSW1 on the keyboard, but on the ROM3 M50741, it is connected to the CP-CNTL jumper that locks the control panel. That implies a different mask ROM without support for the Apple IIe keyboard.

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Tested it

Alright, I tested it this week and totally forgot to say anything, All the connections seem fine surprisingly, there seemed to be continuity betweeen all of the points you said to check..I wanted to check to see if there was a fuse or something on the ADB keyboard that had blown, but I can't see much of it without lifting off the metal plate under it and I haven't had time to remove all the keys this week. I'll try to do it sometime this weekend but I figured I'd give an update

 

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I think you're right..

I think that could have been what happened.. I do recall having tried hotswapping the keyboard in the past, not sure if I was doing it when it stopped working but that could have been what happened..And as robespierre said, I don't appear to have the keyboard or numpad connectors since my board is a rom 3.

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