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LC II Recap + Sonnet Presto LC 040 Accelerator

David Cook

Well-known member
I recently made a mistake winning an auction for a Sonnet Presto LC PDS Accelerator. I assumed it would work in my LC III. Unfortunately, it is limited to Macs with the original LC PDS slot, not the newer LC III PDS.

I chose to double-down on my error by purchasing an LC II that did not include photos of the inside. I was rewarded for my continued lack of wisdom with the following:

LC-II-Maxell-Battery-Leak-Damaged-Top-Metal-Shielding.jpg

Fortunately, the battery damage was limited to the top of the metal case (photo above) and the positive contact of the battery holder (photo below). No traces or other parts were affected.

LC-II-Maxell-Battery-Leak-Damaged-Holder.jpg

However, the motherboard near the leaking capacitors looked extra juicy. I feared hours of trace repair.

LC-II-Capacitor-Leakage.jpg

Here is a close up of the 78L08 voltage regulator. I particularly appreciate the hairs stuck to capacitor C21.

LC-II-78L08-Capacitor-Goo.jpg

For boards with enough capacitor leakage, I begin with an ultrasonic cleaning. It makes desoldering a lot easier. The cleaning machine preheats the solution (Elma TEC A1 https://amzn.to/40SrOJG) to 50C. I find that temperature really helps remove flux paste. The board is cleaned for 15 minutes.

Below is what the board looked like immediately after it dried. Amazing improvement. If you decide to get into recapping, it is absolutely worth getting a large ultrasonic cleaner. Mine cost only $275 (https://amzn.to/42UOevy). It gets into places and removes sticky material that I just couldn't by hand.

LC-II-78L08-Ultrasonic-Cleaned.jpg

Remaining grit and grime is manually removed with a dental pick followed by isopropyl alcohol and sponge swabs (https://amzn.to/40yHHVE). For C22, I did not have a 1uF 50WV surface-mount aluminum polymer or ceramic capacitor on hand. So, I used a through-hole film capacitor. Although bulky, this worked perfectly fine.

LC-II-78L08-Capacitor-Repaired.jpg

For the fun of it, I added a pushbutton switch to the CPU reset line (S1). I did not want to go through my piles of parts in the basement to find an FPU socket, though. By the way, notice that the film capacitor barely fits when the board is installed in the case. (Whoops)

Finished-Recap-LC-II-Motherboard.jpg

Shockingly, there was no trace or part damage (other than the battery holder). I just don't get it. This LC II simply needed a good cleaning and recap, but every LC 475 I buy (manufactured years later) has eroded traces and a mushy PCB. Did the chemical formula for the capacitors change? I mean, they are the same size and capacity. (This was years before the capacitor plague.) Did the PCB soldermask formula change?

RAM and VRAM

Delightfully, the LC II included a 512 VRAM stick from Apple. 820-0605-A. This supports 256 colors on a 13-inch monitor.

Apple-Macintosh-512KB-VRAM-820-0605-A.jpg

The memory slots were empty. Onboard RAM is 4 MB. So, I added two 4 MB sticks to bring the total memory to 12 MB (well, 10 MB due to Apple's software-enforced limit).

68040 Accelerator

The whole point of this is to make use of the Sonnet Presto LC accelerator. This is not the Presto Plus -- this only has the CPU upgrade.

I was confused by the really old mask version and date code on the processor. The card was manufactured sometime in 1997 or later (see the date code of other chips), but the processor is from 1991. I guess Sonnet got a great deal on old stock 68040 chips.

Sonnet-Presto-LC-Accelerator-Front-Side.jpgSonnet-Presto-LC-Accelerator-Back-Side.jpg

The last addition to this computer is a MicroMac fan. I purchased an LC III a while back that had this fan attached to the back. The seller did not include internal photos. So, I assumed there was a PDS upgrade card inside. It turns out the seller had pulled the card and sold it separately. So, I got played a little bit.

Regardless, the MicroMac fan is now being put to good use by cooling the Sonnet accelerator.

MicroMac-LC-II-PDS-CPU-Fan.jpg

The power for the fan is drawn from the hard drive connector with a little piggyback cable. A nice touch.

MicroMac-LC-II-Fan-Power-Cable.jpg

RESULTS

Norton apparently does not display the correct speed for the processor, which Sonnet notes. It should be 25 MHz.

Presto LC Wrong MHz.PNG

I ran various benchmarks, with and without the accelerator.

LC II Presto Rating.PNG

1. Even though the 68040 is a great chip, overall performance requires support from the rest of the board. The IIfx's 68030@40 MHz supported by L2 cache, fast memory, and a full data-bus outclasses the LC II's 16-bit data paths with a 68040@25 MHz.

2. With the Presto, performance degrades from System 7.0.1 to System 7.1.2 This is partially due to additionally third-party extensions that I used back then (and copied over to my MacSD).

3. The benchmarks supplied by Norton for the LC II were tailored to match the expected usage. That is, they used the smaller resolution monitor and they removed even some of the stock extensions. I guess that's not unreasonable if most users did so as well. On a computer with a fast processor and full data paths, the overhead of extra extensions is not significant. But, look how hard it hits my LC II (final row).

- David
 

joshc

Well-known member
Nice work. LC IIs have some of the worst cap leakage, but the traces tend to be OK from what I've seen.
 

djhaloeight

Well-known member
Nice work. LC IIs have some of the worst cap leakage, but the traces tend to be OK from what I've seen.
Agreed. My LC II is completely non functional, yet my older LC still works. LC caps leaked less than the LC II. I’m ordering a hot air rework solder station soon and I already have caps on hand to replace both machines.
 

joshc

Well-known member
Agreed. My LC II is completely non functional, yet my older LC still works. LC caps leaked less than the LC II. I’m ordering a hot air rework solder station soon and I already have caps on hand to replace both machines.
Good luck with the restoration. :)
 

ObeyDaleks

Well-known member
Weird. My LC II with TransWarp 4300 @40Mhz (with cache) scores about 10% better than the IIfx. I would expect a 040 @20Mhz to be at least as fast if not faster. By the way, mine looked just as bad before recap. That one corner of the board was disgusting.
 

DatMac

Active member
I have a similar card but its for a SE/30, does the driver work on this? or if someone here has them because this card wont do anything when plugged in my se30, just boots normal onboard 030.
 

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