Macintosh LC III Bodge-Laden PCB

[macoslove]

I am not sure about these bodge wires but I assume they are first revision last minute fixes, or at least that is the hope.

No chime or video output joy so lets see what some tasty new caps will do for it. Will there be gremlins hidden like with my Quadra 605? I certainly do not want to have green garbled video...

I need friends that have greater skills to teach me to be more capable on the diagnostic realm.

Anyone have info on these LC III's and potential things to look out for?

 

[David Cook]

I am not sure about these bodge wires but I assume they are first revision last minute fixes

Correct. Those are factory.

 

[macoslove]

Well, here's to the next step! No destruction found from the fishy caps and for that I am thankful.

 

[David Cook]

Nice job.

C22 is reversed. That is, although you installed it in the way Apple marked it, Apple made a mistake. You need to flip it the other direction.

See https://recapamac.com.au/macintosh-lciii/

 

[macoslove]

Ah good to know! I guess there were more than just the bodge mistakes with this guy!

 

[speakers]

Nice job.

C22 is reversed. That is, although you installed it in the way Apple marked it, Apple made a mistake. You need to flip it the other direction.

See https://recapamac.com.au/macintosh-lciii/

I got caught by this a few years back. It's a decoupling capacitor on the -5V rail. The original aluminum cap didn't care but if you replace it with a tantalum that'll draw a large current under the reverse polarity. The LCIII PSU won't complain, but the -5V line will droop to perhaps less than -2V. The machine will still boot but, in particular, the serial ports won't work. Note: if you use a different PSU, as I did, it'll detect the overcurrent and refuse to run.

 

[macoslove]

I am glad it was caught!

It now lives again!

Gotta love it!

 

[GiGaBiTe]

If you want a bit of extra performance, there are a few passives you can move around to change the board to LCIII+ spec and run the CPU/FPU at 33 MHz. You'll probably need a heatsink though.

I just replaced the Motorola part with a much later Freescale part that runs a whole lot cooler on mine.

 

[macoslove]

Interesting, I bet I can get a heat-sink for it. I recall the jumper selections on my old 'blue and white' G3 that could adjust the cpu (at cost of warranty). Is this essentially the same idea just without simple jumpers?

 

[speakers]

Interesting, I bet I can get a heat-sink for it. I recall the jumper selections on my old 'blue and white' G3 that could adjust the cpu (at cost of warranty). Is this essentially the same idea just without simple jumpers?

It does require some soldering but it's very simple. See https://lowendmac.com/2014/overclocking-the-mac-lc-series/

A heatsink isn't really required. I did the mod and the cpu doesn't run hot .. but your mileage may vary.

 

[GiGaBiTe]

The jumper block on the G3 does a lot more than just change the CPU clock.

The only change on the LC III involves moving a SMD resistor from the top of the board to the bottom.

LCIII (P450) Speedup

If your CPU is getting too hot or is unstable, you can just revert back to 25 MHz.

The original MC68030FE25B on my LC III must have been a crappy die revision, because it ran smoking hot even at 25 MHz, like you couldn't touch it hot. The Freescale part I replaced it with barely gets warm. I've been told the Freescale part is a remarked counterfeit, but it works and I don't really care.

 

[GiGaBiTe]

Did a bit of research.

The D66C mask revision of the 68030FE25B is made on the 1 um (1000 nm) lithography node in Sendai, JP. It's the last mask version of the B rev 68030 and the smallest. The older mask revisions were either 1.2 um or 1.35 um. I'd sure hate to see how hot those parts ran if mine could nearly boil water.

My Freescale part with the F91C mask revision is actually a legit part number, it was fabbed on a 800 nm process, which explains the reduced heat output. It's the first of the C rev 68030, made around the time when Freescale was spun off from Motorola. There are apparently both Motorola and Freescale marked 68030s floating around, as they seem to have taken their time changing the names.

 

[macoslove]

I didn't even know this was a thing.

For all I know, I know nothing...

Is this the path to the Hemlock?