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Excellent, that rules out any problem with the traces. Well, now we have to think of some other thing to check. After a nice three-day weekend, the work week has resumed for me. I won't be able to respond as quickly as I've been replying previously, but I'm still interested in trying to fix...

Thanks for these posts with the corrected measurements, and thanks for reading my long post. If the non-TTL signal behaviour in the bad CPU board is the same for both CPUs, then we can probably eliminate the CPUs from the list of suspects. Our problems lie elsewhere. From what I can tell: UA16...

Thanks for the update! This sounds like a more likely explanation to me. Congrats on getting to the bottom of it!

⚠️ Please read this entire message carefully before taking further steps. ⚠️ Thanks for the investigations, but I think we are trying to solve too many problems at once. Let's solve one problem at a time. When you try to solve more than one problem at the same time, things become a lot more...

With U8B, U9B, and the boot ROMs removed, the only thing left connected to most of UA9-UA16 is the CPU itself. There's nothing else on the bus. Did you get a chance to look at my question from my last post around swapping 68000s between the good CPU board and the bad CPU board? NOTE: Now that...

Thanks for this. These signals look a lot more like TTL, except for UA12, which is still not able to rise above +5V for reasons I don't understand. The only thing that is receiving UA12 at this point is the boot ROM. From what you've written: when you installed the 68000 from the good CPU board...

It was good to have observed U5B is another chip we have to consider --- I see that it has UA14 as one of its inputs. Additionally, I just noticed that U14F receives UA15 and UA16 as inputs too. If necessary, we can try to understand more about what these chips are doing by referring to the...

PS: It doesn't sound too surprising to me that the CPU and the various memory devices you've identified get hot. Can you compare the warmth you're feeling with the same ICs on your working CPU board?

Thanks for sharing more measurements of U8B and U9B. None of the other pins look mysterious to me right now. Since you've verified that \HALT is remaining high, we can be virtually certain that the CPU \RESET pulses are coming from the CPU executing RESET instructions from the boot ROM...

Thanks for these additional traces. A1-A8 don't look nearly as suspicious to me as A9-A16 do. I'm a little curious about the intermediate voltage level during the \RESET assertion, but given that the computer doesn't do anything while \RESET is asserted, I don't think this is a very important...

Thanks for these traces. And apologies for what I said about pin 2 on both ROMs earlier --- I said they corresponded to different data bits, but I was thinking of the O2 output, not pin 2, which corresponds to UA13 for both ICs. Based on your traces, it looks like address lines 9-16 are...

Thanks for answering all the questions and sharing trace images so quickly. OK, all those signals look just fine, so it's probably the CPU that's resetting itself for the reasons that were discussed in the previous thread. (The CPU can assert \RESET whenever it executes a \RESET instruction.) I...

Thanks for starting the new thread. Thanks to your swapping components, it looks like we know a lot already, which is a good start. It's nice that the problem is known to be localised to the CPU board. If I understand correctly, \RESET is behaving strangely, so let's begin there. Can you share...

Hi @Greniu . Would you like to start this campaign in a new thread? Do I understand correctly that the CPU in the faulty board works when you place it in a different CPU board?

It's a little surprising to me that line filter capacitors should have an effect on the display. Having removed the suspicious caps, do they test OK? I'd be tempted to bet that you wouldn't get the strange behaviour if you put the suspicious caps back in the machine --- that it was something...

mst3k means these ones on the bottom of the arm actuator:

Thanks for this description. This is a promising development for Widget owners everywhere. Please keep us posted on what you encounter tomorrow. I don't think there are any drawings of the internals of the arm actuator in here...

Congratulations! This is a fascinating development, and it may illuminate a new way to deal with this common-seeming problem. Can you be more specific about what you mean by "rotat[ing] the metal cover"? Did you lift it all the way off? If so, did you look underneath the cover? If you did that...

Servo trim pots are a set of potentiometers on the Widget motherboard used for adjusting the optical system that's part of the coarse servo positioning system. You can read how they are used starting from PDF page 44 of this document...

Never, never, never move the arm unless the spindle is turning! In Widget and most other hard drives, the heads never touch the disk surface: they ride on a cushion of air built up by the rotational motion of the disk. When the disk stops, the heads land somewhere (ideally on a "landing track"...