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Old 03 April 2011, 07:00   #1
8bitbubsy
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8371 Fat Agnus in A500 R6a

My A500 r6a originally had a Fat Agnus "CSG 8372A", but that one is now living a happy life in my A2000. My A2000 originally had this "MOS 8371", with no CSG branding or anything. Since I took the Fat Agnus from my A500, I needed to use the A2000 one in my A500. It worked just fine in the A2000, but in the A500 it acts crazy banana!

Most of the times, I get a gray screen with a frantic flickery show, and the scanlines get skewed and stretched and everything. It does not get any further than this, not even to the white screen. If I gently touch the chip the flicker changes heavily. Sometimes it just boots, but it'll crash in a matter of seconds. Crash as in flickery coming back, floppy stopping reading etc.... I cleaned the contacts and checked for shorts on the chip. None... Oh, the PSU is also good, and all caps are changed on the mobo, everything looks great.

So I tried the "CSG 8372A" in my A500 again just to check, and it worked very well. I could touch the chip as much as I want, it was absolutely fine and stable.

This is so weird! The "MOS 8371" can't be that affected by interference? It's crazy! I sense that the newer A500 boards were made for 8372A and not 8371... Any hacks I can do to stabilize it? I guess there's maybe some caps or resistors needed/needed to be removed...

I know that the older A500 boards came with this chip, so it is supposed to work with it. And no, I am not speaking of the 8375R0 found in A500+. That one has a different pinout.

EDIT: PROBLEM SOLVED!
I had to short jumper JP4, it was factory-cut (you could see it)... On 8372A it's for NTSC/PAL selection, for 8371 it's for something else.
I can even touch the 8371 now, it's super stable

Last edited by 8bitbubsy; 03 April 2011 at 07:38.
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Old 12 March 2020, 09:24   #2
kulamario
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I have same setup but I have additional expansion board 501
Workbench see 1mb Chip Ram but Agnus is only 512k
Disconnect JP4 no help me still have issues
Any advice for me lads ?
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Old 12 March 2020, 10:57   #3
Jope
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You should revert JP2 to 512/512 mode if you have the 8371 Agnus.
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Old 12 March 2020, 11:38   #4
kulamario
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But then amiga seem 0.5mb chip and 0.5 slow memory
I want have 1mb chip
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Old 12 March 2020, 11:40   #5
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Then you need a 8372 Agnus, the 8371 will not work when configured for 1MB of Chip.
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Old 12 March 2020, 11:42   #6
kulamario
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Ok this what I thinking
Agnus is a problem
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