Rainbow Islands repair help

PCB problems and fixes
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darksoft
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Rainbow Islands repair help

Post by darksoft »

Hi,

I have a non-working Rainbow Islands PCB. I believe I located the problem on the 4 SRAMS located in IC49,50,51 and 52.

After changing them as some where bad, I still get a OBJECT RAM ERROR. I have noticed that there are some important scratches on the back side of this area and that not all Adress pins in the 4 SRAMS were connected.
I traced all the data lines back to the Custom square TAITO chip, but I couldn't trace the D7 and D8 lines on the IC49 and IC50.

Can someone with a working Rainbow Warriors PCB please provide the following info, so I can repair my PCB:
* Are all Adress pins connected to each other in all 4 SRAMs (All A0s connected to each other, all A1s,etc.)
* Where are bits D7 and D8 in IC49 and IC50 going to?

Thanks in advance.
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Hewitson
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Re: Rainbow Islands repair help

Post by Hewitson »

Hopefully these might be of some assistance:

http://www.jammarcade.net/partial-rainb ... schematic/"
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porchio
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Re: Rainbow Islands repair help

Post by porchio »

Sorry they aren't the best schemes in the world but hopefully the will help you out although don't think 49 and 50 are covered on it.
I should really learn to make better ones ;)

I'll take a look at my board when I get a minute
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Re: Rainbow Islands repair help

Post by porchio »

Behold, a crappy picture :D
Image
darksoft
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Re: Rainbow Islands repair help

Post by darksoft »

Thanks guys, I'm back home on the weekend and will definitely check this and get back to you with (hopefully) another working Rainbow Islands PCB.
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Re: Rainbow Islands repair help

Post by darksoft »

@Porchio,

Thanks to your info, screen looks now much cleaner with much less garbage but still gets stuck in OBJECT RAM ERROR.

I forgot to check the signals -W, -E and -G when I started this post and now I only could track -W from IC51 and IC52 to the TAITO custom. The rest are lost and that's probably the reason why it still doesn't work.

Coudl you please tell me where these pins are going to?

Thanks in advance. I'm looking forward to have this one working again soon!
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Re: Rainbow Islands repair help

Post by porchio »

No problem, ill check it out when I get some time at it, unless anyone else can help
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Re: Rainbow Islands repair help

Post by darksoft »

Thanks! Looking forward to fix this classic!
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Re: Rainbow Islands repair help

Post by porchio »

Had a look at the RAM on mine.
Image

All of PIN 21 (/WE) locations are marked on my second masterpiece
All PIN 20 (/OE) are tied to GND
All PIN 18 (/CS) go to PIN 8 of IC48 (74F00)
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Re: Rainbow Islands repair help

Post by darksoft »

@Porchio.

Thanks! The Board is still showing the OBJ RAM ERROR, see picture.
DSCF9063.JPG
I've checked the conexions and they ALL look OK.I also tested the SRAMS in my Wellon and they all showed OK.

Any other ideas what to search? I hope is not the Custom chip.

See picture of my Masterpiece :)
DSCF9064.JPG
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Re: Rainbow Islands repair help

Post by porchio »

Don't suppose you have access to a fluke 9010 do you?
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Re: Rainbow Islands repair help

Post by darksoft »

Nope. However those SRAMS are only accesed by the Custom, right? or is there any other chip accessing them?
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Re: Rainbow Islands repair help

Post by porchio »

I think the address decoding is done by the PAL20L8 at location IC56 but ill check more thorough later
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Re: Rainbow Islands repair help

Post by darksoft »

@Porchi. I traced all the Address lines to the custom Taito chip, the same one of your masterpiece :)

None of them are going back to the PAL you mention.

The only question I have is that I assumed that ALL 4 SRAMS share the same address bus, which means that all A0-A10 are connected to the same pin in all 4 SRAMS. Could you please check if that's correct?

IF not, I will replace the 74F00 and see what happen.

Btw, what would be the help of the fluke? I thought this SRAM was only accessed by the custom chip and the 68000 had no visibility of it. Is that correct?

Thanks for your help. I appretiate it.

Cheers.
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Re: Rainbow Islands repair help

Post by porchio »

The CPU has read write access to the object ram, well it does on startup at least. If you look at the dissassembly the code is writing a value to the ram, it them reads it back and compares it. If its different then the object ram error is displayed.
The object ram starts at $D00000 so address lines 23, 22 and 20 are required to be high for this. Those upper address lines go to that PAL20L8 so I was assuming that this chip was the decoder to select the ram chips for writing.

I will check the address lines though
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Re: Rainbow Islands repair help

Post by porchio »

You are correct, all the address lines on those RAMs are connected.
What are pins 8, 9 and 10 of that 74F00 doing on your board?
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Re: Rainbow Islands repair help

Post by porchio »

I have now reproduced the PAL chip B22-07 (PAL20L8) if you need it.
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