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Macintosh SE broken ROM LOW chip

giobbi

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Dec 23, 2012
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Hi all,

I have a Mac SE showing a barcode-like pattern:

2015-07-06-3308- BAD ROM LOW.jpg

A friend of mine has the same computer, so we swapped parts until we found the culprit: the 342-0353-A (rom low) chip. I got the BIN image on the web (64 kB), but I don't know if I can use a 27c512 eprom as direct replacement or not; do I need an adapter? In this case, have you some schematics for that?

Another question: can I dump the ROM content simply reading it by my eprom programmer as it was a 27c512? I didn't find the 344-0043-A IWM ROM image and I wish to dump it, just in case... again, if an adapter is needed, I wish to know if you can supply a schematics..

thank you!
 

David_M

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Oct 1, 2016
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Melbourne, Australia
I can read the 342-0353-A ROM in my programmer as a 27512 so an eprom can replace it with no issue. The 344-0043-A gives strange results, so I dont know if it reads correctly or not.
 

ldkraemer

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Mar 14, 2013
Messages
2,102
Location
Chaffee, MO
Giobbi,
It doesn't appear that a 27512 will function properly because Pin 22 is A16 on the APPLE ROM, while it is
OE* & Vpp for the 27512 EPROM. So, you will access to the lower 256K, but without since A16 won't
ever go HIGH you won't be able to access the top half of the EPROM.

ok 10.A0..................VCC..28.ok
ok.09.A1..................O0....11.ok
ok.08.A2..................O1....12.ok
ok.07.A3.....U70.......O2....13.ok
ok.06.A4.....ROM.....O3....15.ok
ok.05.A5.....LOW......O4....16.ok
ok.04.A6..................05.....17.ok
ok.03.A7..................06.....18.ok
ok.25.A8..................O7....19.ok
ok.24.A9..................CE*...20.ok
ok.21.A10...............A16....22..OE*.&.VPP..BAD
ok.23.A11...............A15....01.ok
ok.02.A12...............A14....27.ok
ok.26.A13...............GND...14.ok

2 ^ 15 = 32768 -1 = 0x7FFF but you need 2 ^ 16 = 65536 -1 = 0xFFFF

Does your Binary file of the 342-0353-A ROM have a full image of the Original? I've downloaded a file, but haven't
had a chance to look at it yet.

If you can find a larger EPROM or EEROM you can make an adapter from 30 Pin to 28 Pin and just plug in a larger IC adapter.

U70-ROM-LOW.jpg

Thanks.

Larry
 
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ldkraemer

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Messages
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Location
Chaffee, MO
You should be able to use any of the AMD, TI, Intel 27C010-10, 27C020-10, or 27C040-10 32 Pin parts. Assuming you can program that
specific part, or find someone who can. Then, make a small adapter board from 32 Pin IC socket to a 28 Pin IC Socket.

For the 28 Pin socket you will replace it with a Digikey part number SAM1112-20-ND at $2.57 each. (TS-120-T-A or TS-120-G-A from SAMTEC)

I've created your Adapter Board.


SMJ27C10-10

Vpp.01.................32..Vcc
A16.02.................31..PGM*
A15.03.................30..NC
A12.04.................29..A14
A7..05.................28..A13
A6..06.................27..A8
A5..07.................26..A9
A4..08.................25..A11
A3..09.................24..OE*
A2..10.................23..A10
A1..11.................22..CE*
A0..12.................21..D7
D0..13.................20..D6
D1..14.................19..D5
D2..15.................18..D4
GND.16.................17..D3



SMJ27C20-10

Vpp.01.................32..Vcc
A16.02.................31..PGM*
A15.03.................30..A17
A12.04.................29..A14
A7..05.................28..A13
A6..06.................27..A8
A5..07.................26..A9
A4..08.................25..A11
A3..09.................24..OE*
A2..10.................23..A10
A1..11.................22..CE*
A0..12.................21..D7
D0..13.................20..D6
D1..14.................19..D5
D2..15.................18..D4
GND.16.................17..D3



SMJ27C40-10

Vpp.01.................32..Vcc
A16.02.................31..A18
A15.03.................30..A17
A12.04.................29..A14
A7..05.................28..A13
A6..06.................27..A8
A5..07.................26..A9
A4..08.................25..A11
A3..09.................24..OE*
A2..10.................23..A10
A1..11.................22..CE*
A0..12.................21..D7
D0..13.................20..D6
D1..14.................19..D5
D2..15.................18..D4
GND.16.................17..D3

I've got the adapter completed, so you should be able to have some Adapter Boards created. I'll send you an email with the info.



Larry
 
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giobbi

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Location
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I can read the 342-0353-A ROM in my programmer as a 27512 so an eprom can replace it with no issue. The 344-0043-A gives strange results, so I dont know if it reads correctly or not.

Reading the 344-0043-A as 27512 returns a page full of FF; I'm not sure about the ROM size however. Maybe it should read as it was another kind of eprom (i.e. 27256).
Strange you can't find any BIN image of it on the web.

EDIT: --- I've found the IWM stands for Integrated Wozniak Machine disk controller, so it's not a ROM...
 
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