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Levco MonsterMac 2MB Teardown & Repair


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As for the type of ROM ICs used here, they're almost certainly 27 series EPROMs. I think they would be very unlikely to be mask ROMs given limited production numbers, plus the fact the sticker says "PROM" on it. They're also very unlikely to be EEPROMs as those were fairly exotic at the time. I strongly suspect that these are a pair of 27C256 or similar EPROMs.

(EPROM = Erasable Programmable ROM, typically erased with a UV-C lamp, EEPROM = Electrically Erasable Programmable ROM, typically erased out-of-circuit with a programmer that can supply the higher erase voltage that's not seen in-circuit, along with setting an erase pin.

EPROMs and EEPROMs can be easily read with a modern programmer, such as the TL866II+. I recommend peeling back one of the labels to verify the IC's part number to select it in the programmer software. You don't have to worry about household lighting or sunlight shining through the quartz window on top of an EPROM and erasing it. It requires a specific wavelength of UV-C light that doesn't make it through the atmosphere, nor is it released by artificial lighting other than true germicidal lamps or unshielded arcs like welding. If you don't want to peek under the label, the software does offer some auto detection capability. Once the correct IC is selected, you can read the contents and dump it to file. I picked up a TL866II+ this year and dumped my original Radius SE Accelerator ROMs, successfully programmed another set of EPROMs with the latest version to fix a stability issue with the SE FDHD, and enable use of System 7.


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The Logic chip is frequently used to upgrade a 128 k board to 512.

This board is an original 128k board, not the 128/512 one used later with both markings.


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Most of the 512 boards I have seen are the dual-marking type. Did Apple upgrade 128k boards like this, or was this a third-party upgrade? I thought they just did a logic board swap. I certainly wasn’t aware they socketed the RAM chips.


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The convention is that the stripe on the cable goes to pin 1 on the connector. Whether they followed convention, I couldn't say.


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In case anyone runs across this old thread, here is a link to an article on the MonsterMac from the May 1986 issue of Apple User (link), page 16. It discusses the installation process, starting with a 128k -> 512k RAM upgrade, and then adding the MonsterMac board to bring the total to 2mb.


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Slightly OT, but a few years back I acquired an original Macintosh with a similar upgrade - first the "piggy-back" upgrade to 512k, then a 1.5M board placed on top - for 2M total. The company behind this upgrade was Perspect Systems, Inc. Not much out there in web-land about them.

Here are some pics :