Performa 5200CD died. related to CUDA maybe but stuck.

[ImmortanJoe]

Nope, that's a custom part. 0120 is shorthand for 343S0120. You could theoretically replace it with some other battery voltage monitor IC, but that would need a bodge.

It's not exactly a museum piece. I'm fine with bodging in something else. But I still want to dig deeper first. The voltage on the 0120 VRTC pin going back up to VBATT while the CUDA is probably resetting during / after pressing the CUDA button really makes me uneasy. I just can't see what could be causing that behaviour. My gut says that an output from the CUDA is shorted to ground which could explain why the voltage goes to about VBATT during reset and current drops to nearly 0. If that's the case then I need to check a bit more, and depending on the result possibly give up.

 

[GRudolf94]

Cuda isn't exactly a complex beast. The pinout is there and it never changes between machines. I don't think it's got anything shorted, else the machine probably wouldn't operate without the battery. Really, the easiest way to go about this is remove 0120 and see what sort of consumption you get by feeding Cuda pin 13 directly with those 4.5V. It letting the rail float to full voltage during a reset does sound kinda weird, but yeah, that'll tell you.

 

[ImmortanJoe]

Cuda isn't exactly a complex beast. The pinout is there and it never changes between machines. I don't think it's got anything shorted, else the machine probably wouldn't operate without the battery. Really, the easiest way to go about this is remove 0120 and see what sort of consumption you get by feeding Cuda pin 13 directly with those 4.5V. It letting the rail float to full voltage during a reset does sound kinda weird, but yeah, that'll tell you.

Well remember it powers up with no battery but that's it. No signs of life from the logic board. With the battery in it doesn't even power on.
I've considered something like your suggested approach to see what happens. Ive also considered bypassing it in a different way so VTRICKLE is directly supplying the CUDA. I just don't quite get the role of TRICKLE_D in that case.

 

[GRudolf94]

Theoretically how this should work is: TRICKLE_D (TrickleDetect) is an input on Cuda - it senses that the machine is energized because the power supply has raised the 5V_TRICKLE line. It presumably won't attempt to power on if that is not detected, or at least I don't think it generates a power-on reset.

 

[ImmortanJoe]

Last night I did a quick test of going from VBATT to VRTC on the 0120 with my multimeter on mA with an 18650 providing power to the circuit through the battery connector because I was being a bit lazy. About 30mA still. So it certainly seems that the CUDA is drawing that current. But it also seems to be working so it seems even more likely that something on one of it's outputs is drawing more current.

I also made a second discovery. One of the springy ground things under the board had been bent and looked like it had been contacting a via near the ROM because the solder mask was worn off and the via was shiny. I really hope this was something that happened while I was testing the board. To be safe I re-bent it a bit more and put some kapton tape over the potential contact point. Plugged into the computer it doesn't even come close to making contact, so I don't know.

After my pointless testing I plugged the "bare" board in, added power and turned it on using the keyboard. It turned on and stayed on. Not much else happened obviously because there wasn't even the ROM or RAM in it. So I tried adding the ROM and RAM and it would only "bump" on for a couple of seconds and turn off again. Removed the RAM and ROM and this was still the case. Kind of gave up, put everything back in and back on and tried a power up again just in case. Still the same. It's been put aside for now.

Last night I ordered the SMD caps for it and the MOSFET that I'm slightly suspicious of. I also ordered caps for the 7300/200 motherboard, CPU board, and hopefully the needed parts for it's PSU.

I really need my scope. I feel like I'm working blind.

 

[ImmortanJoe]

Theoretically how this should work is: TRICKLE_D (TrickleDetect) is an input on Cuda - it senses that the machine is energized because the power supply has raised the 5V_TRICKLE line. It presumably won't attempt to power on if that is not detected, or at least I don't think it generates a power-on reset.

You posted while I was typing. I'm really going to need to work out a way to check that the 5v trickle rail is good. I think about the only way is with a soldered on flylead. At least with the classic macs I could sort of eviscerate them on a table and power them up.

 

[ImmortanJoe]

The components I ordered arrived. For the 5200 it was just SMD caps and a FET just because. I put in the new caps and FET. No difference. I realised I can easily check the 5v trickle voltage from the ADB connector. No problem there. 4.96v. Jump starting it from the connector without the keyboard yielded the same momentary on issue. I guess it's time to go deeper.

 

[ImmortanJoe]

I was doing some digging on the internet. Most of my searches led me to posts on 68kmla, which I take to be a positive thing because it means that I can potentially be asking some of the same people. First, for others in the future that may be trying to find this little bit of information, _PFW = _Power Fault Warning.
While I haven't tested yet, I do find it interesting how on a couple of different schematics _PFW appears to be handled by the CUDA. Can someone please tell me what criteria the PSU considers to be a failure? As I said I haven't tested yet but it would be useful for faultfinding. I'm not sure if I said it earlier in my thread but one thing I have suspected is an overcurrent condition. I haven't seen any sag on the +5v or +12v rails but it's another thing to consider. I really wish I had one of my crappy ATX supplies on hand that I use for testing things so I could give this logic board an out of body experience.

 

[ImmortanJoe]

I just realised there's a trace on the schematic going from the stuff near the top left to vCuda. I feel silly that I missed it but the circuit makes a bit more sense to me now.

 

[ImmortanJoe]

I decided to go ahead and remove the 0120 just now with what I have. It's off, and VRTC is still getting power when the battery is connected at about 0.8v less than VBATT. This is ...interesting. I'm going to have to do some probing because I can't see anyway on schematics that it could leak so there's got to be a bridge or something. I don't know.

e: 0.4v difference without the 0120

 

[ImmortanJoe]

It seems at least to a degree that the 0120 isn't directly controlling the flow of power so the schematics don't apply as directly as I'd hoped. At least one of the nearby SMD transistors (that's what I assume. I haven't checked their code yet) appears to be involved in switching VBATT to VRTC. It's a bit hard tracing it properly when there's still a rogue component.

 

[ImmortanJoe]

I was waiting on some low melt solder to make this whole thing easier but it got blocked at customs. Not a clue why. As far as I know it's not a banned item, and eBay sellers sell the exact same one with a decent markup! And as silly as it seems I got a better desk lamp which will help a lot. It's hard doing this without access to my stuff.
Unrelated but I got my hands on a G3 iBook clamshell on the weekend. It's the newest Apple product I've ever owned. Don't know if it works yet. I'm not an iThing fan but at least it's a pre-OSX PPC mac.

 

[ImmortanJoe]

FD9, the 3 pin thing just to the right of the 0120 seems to be a regulator, or something to that effect. It's getting battery voltage and appears to be outputting 3.6v, which seems to be connected to the vCuda trace for the 0120. This is with the 0120 removed so I could find the source of the voltage on vCuda. I'm not 100% certain of this but on FD9 the left pin reads the same as the battery voltage, middle 3.6v, and right is gnd.

 

[ImmortanJoe]

Did I say that after being stopped by customs that low melt temp solder paste eventually arrived? I used it to reattach the 0120 tonight because I wanted to try it. Woweewow! It's like magic!
I revisited the PSU just in case. I'm glad I did. From all the plugging in and unplugging the solder on the IEC connector had partially broken free. Fixed that and reflowed some solder joints which looked weird and had flux around them. Previous repair maybe? Put it back together, used some screws I got recently to replace all the missing shielding screws and gave it a try. Fan spins up again which is nice. I can hear the CRT too. But the computer is still very dead. Not even the power light.
Unless someone has any suggestions I'm going to finish putting it back together and shelve it for now.