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Old 17 October 2011, 20:17   #1
A500Man
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EPROMs too slow?

Hi there,

I own an Amiga 500 with a Kickstart 3.1 original chip. To preserve the original Chip I ordered "AMD 27C400-150" EPROMs and had the data contend of the original Kickstart-chip programmed onto a 27C400-EPROM.

Now, placing the EPROM onto my Kickstart-Switch makes no problem, it is working fine. But placing the EPROM directly into the ROM-Socket on the motherboard (Rev. 6a) results in permanent reboots / black screen. I doublechecked and veryfied; the EPROM`s content matches the Original 100%.

Well, what is that? Is the EPROM too slow? I guess not, since I heard of working EPROMs with a speed of -200. But why does it work in that Kickstart-switch (2 Kick-Sockets, one 74LS00-chip) but not stand-alone?

What could it be? Can I "heal" the problem or can I bin the EPROM? Anyone with an idea?

CU,
A500Man
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Old 17 October 2011, 22:37   #2
yaqube
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Was your kick-switcher populated also with the original kickstart chip? If so does the 27c400 work in the switcher alone (the other chip removed)?
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Old 17 October 2011, 23:02   #3
A500Man
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Yep,

I tried the Kickstart-switch with (only) the original Chip; it worked.

Does anyone know what the speed of the original Amiga Kickstart 1.3 is?

Hm, the original Kickstart 3.1 is on a "MX23C4100". It does not state a timing, but the MX23C4100 is avaiable in -100, -120 and -150. I fear the Amiga-ROMs are the -100 or -120 types ... Can anyone verify?

CU,
A500Man

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Old 18 October 2011, 00:07   #4
yaqube
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Quote:
Originally Posted by A500Man View Post
I tried the Kickstart-switch with (only) the original Chip; it worked.
Does your 27C400 work in the kick-switcher with empty second socket?
The problem might be caused by lacking pull-up resistors on the motherboard.
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Old 18 October 2011, 00:26   #5
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150 is too slow for Amiga use sadly.

Get 100ns ones or at worst 120ns.
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Old 18 October 2011, 00:40   #6
A500Man
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@yaqube: Sorry, ma english is not too good, I got you wrong. Now I understand: No, when I place only the original Chip and NO other ROM-Chip on the Kickstart-switch the Amiga does not boot. The same for the 27C400.

What do you mean with pullup-resistor? Could I solder an resistor to the 27C400 to help solving the problem?

@mfilos: I tried it with an "AMD 27C400-105" a few minutes ago; the same Problem: permanent re-boot.

CU,
A500Man
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Old 18 October 2011, 00:48   #7
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@yaqube: Sorry, ma english is not too good, I got you wrong. Now I understand: No, when I place only the original Chip and NO other ROM-Chip on the Kickstart-switch the Amiga does not boot. The same for the 27C400.

What do you mean with pullup-resistor? Could I solder an resistor to the 27C400 to help solving the problem?

@mfilos: I tried it with an "AMD 27C400-105" a few minutes ago; the same Problem: permanent re-boot. But as I reported: Placing the EPROM on the Kickstart-Switch makes it run.

CU,
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Old 18 October 2011, 09:21   #8
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Seems too strange to be a speed problem... The A4000 mobo has jumper to select 160/200ns speeds - which is far slower than the 105 you are testing with and the A4000 is much faster

Maybe the ROM socket on your mobo has a loose pin-hole? As it works in your ROM swapper -are the legs of your ROM swapper larger?
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Old 18 October 2011, 11:47   #9
voxel
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hi :-)

what is the version/revision of your A500 motherboard ?
what is the screen color displayed when the eprom is on the motherboard ?
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Old 18 October 2011, 17:21   #10
yaqube
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Quote:
Originally Posted by A500Man View Post
@yaqube: Sorry, ma english is not too good, I got you wrong. Now I understand: No, when I place only the original Chip and NO other ROM-Chip on the Kickstart-switch the Amiga does not boot. The same for the 27C400.

What do you mean with pullup-resistor? Could I solder an resistor to the 27C400 to help solving the problem?
I had the same issue: http://eab.abime.net/showthread.php?p=525862#post525862

If your motherboard revision is 6 or 8 just populate RP106 and RP107.
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Old 18 October 2011, 23:41   #11
A500Man
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Jepp,

thank`s yaqube! You gave me an idea and I did some research: the 27C400 has a usual power consumation of 15 mA. The Original Kickstart chips consumes 50 or 60 mA.

Hmpf.

CU,
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Old 13 June 2014, 20:48   #12
rampartsagain
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Does any one knows if amga can work with faster kickroms like 50 or 70 nanoseconds ?

regards
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Old 16 June 2014, 15:35   #13
hooverphonique
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Originally Posted by rampartsagain View Post
Does any one knows if amga can work with faster kickroms like 50 or 70 nanoseconds ?
As long as they are as fast or faster than the originals, it should work..
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Old 17 June 2014, 21:36   #14
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Quote:
Originally Posted by mfilos View Post
150 is too slow for Amiga use sadly.

Get 100ns ones or at worst 120ns.
Not true, Ive used 140 and it works perfectly fine.
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Old 18 June 2014, 06:19   #15
tom256
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Does any one knows if amga can work with faster kickroms like 50 or 70 nanoseconds ?

regards
No, access time is set pernamently.
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