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Jeff d - I will have to get back in more detail when I get back on the project.
However, you mentioned that there are "some Apple folks" meeting in Springfield next week. I won't be able to make that gathering but I would really like to get into the loop that even knows that a gathering of "Apple folk" is happening. If you could help me get in touch with the organizer, maybe I can make the next gathering.
Thanks for your help as always
Yes, the 200K is part of the power-on reset circuit for the ADB MCU. That plus the reset switch on the keyboard should cause it to pull the RESET.L line low for a short time to reset the motherboard. If you are sure that pin 49 is not connected (and that the trace it connects to is not shorted to another trace nearby), then you are correct in looking for what is pulling the line high. Everything else it connects to should either be an input or an open-collector output. So if pulling the line high through a 10K resistor does not work, then you need to find what other connection is pulling it high. Looking forward to seeing what you find.
It's here: Kansasfest I believe the response to this new venue was very favorable and they will likely be back there for 2025.
I am able to spend sometime on this project again.
Here are some answers to questions that were previously asked and I was not able to respond until today.
Someone was wondering if I had a BOR(brown out reset) happening. I do not, the +5V line on the oscilliscope is rock steady.
Also asked was what happens when the keyboard is not connected. I removed the keyboard and there is no change. The RESET.L line jumps to +4.8 and after 20 seconds it sawtooths down to what I thought was zero volts. I took a closer look and it really drops to about 100 mV.
Finally, someone wanted to know what the ground looked like when the RESET.L line was dropping. It starts to see all sorts of noise and when the RESET.L stops dropping the Ground line no longer has any noise on it.
Thanks for any help anyone can offer.
Have you tried adding the 10K pullup to the RESET.L line?
Since it sounds like you're near Chicago, if you need to find someone to help repair your board, consider visiting the VCF Midwest retrocomputing convention in early September -- there will definitely be someone with the skills and knowledge, and they may even have a booth and can perform the repair at the show (so bring your IIgs with you):
https://vcfmw.org/
Dr. Webster .. Thanks for the information. I have put it on my calendar and plan to be there on Saturday. I have also added myself to their mailing list. It sounds like just the place to find a repair person.
As mentioned before, getting help from somene who knows the circuit and can poke around with the board would be a great option at this point. Hopefully there's someone at the show which would match the description.
Hopefully it's not just "power user" level folks... this is one that seems to be a bit more than than the "normal" problem level.
Can I ask, what's going on here with the keyboard micro? We touched on this before when you shared this picture....
kbd micro.PNG
Did you ever get that repaired? This picture was takem after you tried to lift pin 49? It appears you (and I admit I'm making assumptions) you may have damaged the pad and bridged 48 and 49. It definately looks like that pad may not be right and trace torn but hard to tell with that picture. Do you have any higher resolution and better focused pictures of that part? If pin 49 is not connected RESET.L would be floating as keyboard micro is responsible for controlling that line and unless there's a drive all bets are off.
As mentioned before pin 16 (the RC reset) you're seeing that held low for at least 200ms and some point after should get pulled up to 5V so we're good there, this is where the ADB micro takes control of the output RESET.L line to the rest of the board. Can you check, if there's something wedged between pins 18 and 19? In that pictures there's something unclear and while it appears both pins are NC so it may not matter but I don't have anything to verify that's correct.
Since it looks like pin 49 is no longer connected to that trace I like Jeff Mazur's idea of manually pulling that trace bound for pin 49 up to 5V via the 10K resistor. I think it's worth verifying that pin 49 is not connnected to RESETL first and then that via which the red arrow bisects should be RESET.L where you could pull that up. But need to make sure pin 49 has no connection with that trace and that via is really RESET.L If you're still getting reset at ground you know the problem is somewhere else.
I have never had the pin repaired. What exists now is the pin does not seem to be connected to the chip. My multimeter says the pin is not touching the chip. I have moved the pin and it is not touching any other pin or pad. The pad above the pin is connected to this pin and in turn to the RESET.L trace. The ADB microcontroller chip is not putting the HIGH voltage onto the RESET.L trace. However, as I said, there is about 4.8V on the trace for about 20 seconds before it saw tooths down to what I was calling ZERO volts. I have now revised that to about 180 MV. My ground fluctuates because of noise in the oscilloscope between 0 and 63 MV. My logic says that if everything were working properly, I could add about 5V to the trace and the system should boot up. Obviously that is not the case.
I tried this evening to add 5V through a 10K resistor. It seemed to add about 50 MV to the voltage on the RESET.L line. I measured the voltage before applying it to the circuit and it was at 4.77V.
Someone also suggested that I reverse the leads when I was measuring the resistance of the RESET.L trace. With the coomon lead connected to ground and the positive lead connected to the RESET.L trace, the resistance is 4.3M ohms. It is with the leads reversed that I get the 57.8 K ohms. I don't know exactly what this means.
I am not going to do anything else on the board until after I have been to the Vintage Computer Fair in Schaumburg, IL on Sept. 7 and 8. Hopefully someone there will be able to steer me in the right direction.
As always, though, I am very appreciative of all the help everyone has been. I realized when I started that it was going to be a challenge.
I just looked at the list of exhibitors for the show and Adrian Black is going to be there. I have watched several of his youtube videos where he repaired Apple hardware. Maybe he can fix my IIGS!
That's confusing, how can a pin not be connected to the chip? The pin is the lead that comes off the chip... did you mean pad? The pin (pin 49 should be both putting at 5V after the reset singal on pin 16 goes hight. Without that pin being connected to the pad (and trace) the ADB micro is not in control of RESET line! If pin 49 is high then than would be something to get repaired and the pad doesn't look in great shape from that picture.
Well that sounds like the problem, if you had the meter in line between the resistor and reset line you likely see the 5V current flowing to ground.
The reason for suggesting reversing the leads on the resistance test is to see if current flows different directions. But when you use M with Ohm do you mean mili or Mega? It looks like you mean mili, but mili is represented with a lowercase m, the capital M is MEGA meaning 1 million and that's a 10^9 difference! When talking about the voltages you say 50MV and 63MV and you appear to mean 50/60 mV. But when talking about resistance you say 4.3M ohms. Is that still mili or Mega? 4.3m Ohm would be a short which would be soemthing to figue out because that doesn't sound good.
FWIW, I get 4.8MOhm from Reset to ground, and 2.8MOhm from ground to reset.
There does not appear to be any devices connected to reset, there's like a few ICs and the CPU unfortunately most of those are surface mounted parts that can't be easily disconneced from the reset line.
At this point my random guess would be something related to the disk drive port, so the IWM. Either plugging in a mac 3.5 drive that's not compatible with GS smartport or accidently plugged in a drive to a powered system. The same can happen with ADB but since ADB looks to be currently out of the loop may not be a good suspect.
Hopfeully you can get some help next month!!
Jeff d wrote:
Well that sounds like the problem, if you had the meter in line between the resistor and reset line you likely see the 5V current flowing to ground. I did not have the meter in the circuit. I am reading these values off the oscilliscope. I was using the oscilliscope to read the 4.77 V as well.
Jeff d wrote:
The reason for suggesting reversing the leads on the resistance test is to see if current flows different directions. But when you use M with Ohm do you mean mili or Mega? I am using the wrong "m" when I was referring to the voltages. I in fact should have been using mV as the unit of measure. However, the capital M is correct for the ohm readings. I rechecked my multimeter with a known 200K resistor, In "auto" select mode it reads 199.7K ohms. When I manually change the scale to read in M ohms, it reads .199. Now that I have clarified my units of measure, is there anything to be learned?
Jeff d also wrote: FWIW, I get 4.8MOhm from Reset to ground, and 2.8MOhm from ground to reset. My value in one direction is very similar to yours but in the other mine seems to indicate a path to ground that gets worse as that part of the circuit heats up. Am I drawing the right conclusion?
As far as pin 49 on the ADB is concerned, I guess I don't know what the exact problem is. What I have determined is that pin 49 never goes HIGH. Whether the pin is not connected to the chip or the ADB is not functioning may not be clear. I guess I thought the pin breaking off the chip was the more likely situation. In anycase, adding voltage to the trace does not resolve the problem.
Jeff - I really do appreciate your help and commentary. I know it is a challenge to try to help someone troubleshoot remotely!
Thanks for clarifying, that makes perfect sense with the voltages. When measuring resistance, that's where things got confusing.
Hmmm, changes with heat.... that is interesting but it may or may not really mean anything. All depends on how much of a change and how much heat. Whatever part of the circuit which heats up (if extreme) could be an indicator of where the problem lies.
Your choice of words here is still a bit unclear.... the pins are the small metal leads that come from inside the chip. The picture of the chip you shared before did not have great detail for that section of the chip so there's a lot of guessing of what's going on there. Are you saying the pin itself is, in fact, broken off the chip? That doesn't appear to be the case, but the pin does look to be dis-connected to the pad (the small metal solder point on the board). If it is connected to the pad, that pad may not be connected to the trace (the wire running from the pad to the rest of the circuit).
I know you're putting this on the back burner until VCF but if you happen to have any better pictures (better lit, different angle, clear focus) of the pin 49 area of the chip that may answer some of these questions.
If it wasn't clear earlier, the ADB micro is responsible for controlling the reset line, the rest of the system components monitor the signal and most can pull the line low when needed (this is the safety mechanism where chips can tell the system to reset, but it's one-way street (pull low) they can only initiate the reset when a problem is detected). As I understand it, and there's some black box stuff happening inside these parts, the ADB micro has both a reset input and output. The reset input (pin 16) is use just during startup, it's that RC node that's connected between 5V and pin 16. That singal/pin is used to keep the system "off" for a few hundred miliseconds while the circuit power gets to a stable point. After the input to pin 16 goes high then the ADB micro controls reset siginal which should be pull high so the system gets running. If your pin 49 never goes high it either means: pin 16 doesn't go high (but you said it does); there's a problem inside the ADB micro; or another chip is pulling that line to ground. But checking if p49 goes high can only be done when pin 49 is not connected to the cirucuit. Because when pin 49 is in-circuit and another part pulls reset to ground (becaues it's sensing a problem, or internal damage) then ADB micro output will be at ground too. (ie Even if the the ADB micro internally is driving the output high that output will be low.) Unfortunately the way to determine what's pulling reset low would be to start disconnecting the reset line from all the chips which are tied to reset line. That's work I suggest you don't do, there's a lot that can go wrong and looking at the ADB micro pin 49 suggest that attempt may have created additional problems and I also don't see cutting traces is a great option. AFAIK the 65816 can only react to reset, it doesn't have any internal way to reset a system so unless there's some serious internal damage that isn't a good suspect but it could be pulled and checked....
My money is still riding on the IWM as the guilty party just because there are so many ways that part can be easily damaged. I look forward to your update in a few weeks!
Here is a closeup of the ADB chip:
Pin 49- small.jpg
I guess I don't know why but pin 49 never goes HIGH. The wire attached to the pad is something I soldered. It is attached to the RESET.L trace and it made it a convenient spot to add voltages to the trace or check the voltage of the trace.
Well that's better but still not great, I can't really tell what's going on with pin 49 and the pad. The previous picture looked like the pin was lifted now it doesn't look lifted. Persepctive is a funny thing or maybe you welded that back down?
pcbishaf wrote:
I guess I don't know why but pin 49 never goes HIGH. The wire attached to the pad is something I soldered. It is attached to the RESET.L trace and it made it a convenient spot to add voltages to the trace or check the voltage of the trace.
First just to get terminology on the same page, the wire/resistor or whatever is soldered to that "pad" is not actaully a pad, but it's a via (trace through the board) which has been filled in and looks like a pad. Pads are where components are soldered through-hole or surface mounted devices (SMD) are solderd to the cirucit with the pads.
Simply put (and I think we've said this previously ) if pin 49 is lifted (meaning not soldered to the pad and elevated away from the pad) (I'm not suggesting you do this again) but rahter mentioning because it sounds like you did this before and I'm just restating that. So, when pin 49 is lifted and it does not go high after pin 16 goes high, then it sounds like ADB micro is bad. I say that because you said before: power supply is putting out good and stable power, and pin 16 goes high after a couple hundred miliseconds. Pin 49 would go high as soon as that startup delay passes. At this point, if that's all correct the only way to attempt to fix is rework that board and replace the ADB micro, but those aren't just floating around. You'd need one of us who can do that work if you really wanted to fix. But costs for that can be expenseive so a new board may be a better option. If you decide to find a new board, I'm still very interested in what's actually happneed to this board. =) Just let me know if you find you don't have a use for it.
Jeff - thanks for the quick response. You wrote the wire I have soldered to the booard is at a "via." Yes, this solder passes through the board to the other side but it is also connected to the "pad" that pin 49 is connected to.
You stated that with this new information, it seems that the ADB is probably bad. It maybe bad, but that does not explain all the readings I am getting on the oscilliscope at startup. The slight delay before the RESET.L trace goes high, the saw toothing down of this voltage to about 80 mV, and the fact that adding 4.77V to the trace does not move the voltage on the line significantly.
BTW, I have two IIGS boards. The second one seems to be in worse shape then the one I have been trying to troubleshoot. This one, the RESET.L line does not move off 0V. I'm probably going to bring them both to the fair. Maybe I can work some type of deal to end up with one good board and the remaining board offsets the cost of the repair or at least can supply the parts for the repair.
As I said, I was going to the Vintage Computer Fair this past weekend. In particular, I was going to see Adrienne Black, a youtuber who has repaired IIGS motherboards. I did speak to him and he was not interested. However, he did offer the name of a friend of his who probably would take on this repair project. I thanked him and decided to wander around the show for a few minutes. Something very unexpected happened. I rounded the corner and sitting on a table was an Apple IIGS for sale. I had checked the pricing on EBAY and the were running about $300 - $350. This hobbyist wanted $275 which I thought was a little too steep without first talking to Adrienne's friend who does electronic repair work. I took his name and email address and moved on. Rounded another corner and there were 3 Apple IIGS for sale. These were just the case, power supply, 1 Meg memory card, and the mother board. These were only $200. So I asked him if he could boot up what he had. It should go the the screen that says no keyboard or mouse detected. Sure enough, that is exactly what happend. I purchased it figureing round trip freight to GA would be $75 which would only leave $125 for labor and parts. It didn't seem the reapir could be less than $125 so I bought the IIGS. Just to give you a feel for the "merchants" there, he couldn't except a credit card. Fortunately he had a PayPal account, which he rarely uses, and I was able to pay him that way.
I brought my 2 boards back and I am going to email the repair person to get a feel for what his fees are. However, I think I will probably just continue on my trial and error troubleshooting project. It will probably be several months before I can get back to this project, but hopefully those of you who have offered help will continue to do so as I post new information.
Thanks again for all you good advice.
Btw, his name is Adrian.
LOL! Who pays attention to details like that with youtube personalities?
Adrian may hit all thee VCFs! Not surprised he's not interested. These can be quite difficult to fix and often the best option is the path you took! This is is still quite different than the other IIs, it's an impressive architecture. Can be difficutlt!
I'm glad you got something that works for a decent price!! You took a good path because these are often more costly to troubeshoot and fix!
As menitoned before, if you want somene to take a look, I'm also in the southeast. No gurantess, I've fixed a few but also been stumped a couple times too.
Not sure about YouTube personalities, but most of the regular dudes I know don't particularly enjoy people using the female version of their names. :)
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