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Good point! Also based on @techknight advice it's important to power both positive pins in the 4-pin Molex if you haven't done so, otherwise something might get fried.

Are any drives (flopy/hard drive) connected? If not, probably makes sense to just keep the mainboard + speaker + screen connected. That seems reasonable as far as I remember. That also seems reasonable. Does it shut off on its own? Does the current draw return to 50mA then? This is...

Congrats on the somewhat working Portable, it's great to see those coming back to life! (with some resistance) @ironborn65 what exactly was the pattern on the screen? According to my research and experience, without SWIM it should bong and end up with a clean "grey" boot screen (but without the...

Maybe interesting - a year ago I bought 2x3 cells here (I know this distributor since the time I've been living in Poland) and reconditioned 2 Portable batteries: https://www.tme.eu/ch/en/details/cyclon-x/acid-cells/enersys/0800-0004/ These are basically identical cells like the original ones...

I can confirm that, had the same with my CII - had to rewash it (and even desolder the EGRET) to fix it months after the initial recap and wash which was pretty thorough.

I would bet on the cap goo or rotten traces around the RTC chip (DIP8, next to the battery) or the clock crystal oscillator (tiny metal can next to the RTC chip). I would clean this area (again) and double check the traces there. I think there was recently a case of a broken RTC chip described...

I can only suggest that the intermittent boot behavior of my Classic II was fixed by desoldering and cleaning the cap goo under EGRET.

I realized I still have two units of my original batch that I planned to sell (but the thread disappeared in the forum crash) - if you're interested just shoot me a PM! https://68kmla.org/bb/index.php?threads/fs-2x-macintosh-classic-ii-fpu-card.40593/

@nnn C16 is connected to the always on +5V rail so that sounds good, it seems that the regulator is working fine: Could you answer a few questions just to make sure we're on the same page: How do you power the computer? You clip your power supply directly to the battery terminals? If you use...

I'm actually the author of this project and I can say I had good luck with this seller: https://www.ebay.com/itm/361103442882 So far all 68882 worked happily at 40 MHz (not that it matters much, it's marginally faster than the 16 MHz bus speed as @max1zzz pointed out).

Can you measure the voltage on the +5V line? I have one dead M5120 where Hybrid is shot and the 5V regulator just doesn't work. If +5V is fine, could you check what are the levels on SYS_RST and SYS_PWR? The official schematic for Portable is available so that should facilitate the...

@joshc are you providing power to all 4 pins in the Molex power connector? @techknight indicated in several posts back in the day that connecting only to a single positive pin might fry some of the logic pins and indeed, if you look at the schematic (it's available), you can see that they're...

I support this view, had exact same problems with some cap goo stuck under EGRET. Had to desolder, clean and solder again.

Hi, Just out of curiosity I was looking into how accelerators are designed for Macintosh SE. I know that some of them just plug into the socket instead of the original 68000 CPU and then the situation is clear. But what is exactly happening with PDS accelerators when the onboard CPU stays in...

I don't have enough experience to say statistically. For sure the backlit version has the advantage of all components being "serviceable", with non-backlit if the hybrid is eaten away/cracked you're out of luck (hopefully at some point someone produces a replacement).

Given my recent journey with two Portables I'll try to answer some questions :) Backlits still have a few electrolytics caps which leak the same may as on the non-backlit version. The power manager chip (PMGR) is the same and also compatible with Powerbook 100. The power circuits differ and the...

So this story reached a happy end :) @mdeverhart was spot on: Thanks a lot for this comment that made me just unsolder a few of them and solder back in one by one. Indeed one of the caps (C11) was shorting to the nearby tracks which lost their soldermask which was eaten away or crumbling...

Seems to be ~1ohm so pretty much a full on short. I will take a closer look at all my interventions in the following day and report back, maybe I bridged something accidentally.

Thanks a lot for suggestions @techknight, they helped me a lot! From what I could see, they are always either $00 or $90 so RAM and ROM (including the ROM overlay). Nothing else. BERR stays high no matter what so no bus error. That's spot on! :cool: I started poking at various lines using a...

Ok, I was digging a bit more into the SYS_RST problem. As a reminder, I seem to be seeing a very regular SYS_RST trigger every ~370us (~2.7 kHz), which prevents the machine from booting. This seems too regular for a floating pin or a bad connection. So I started with continuity checks between...