1MB Chipmem only appearing Amiga 1200. Help!!

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mamejay

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Hey everyone,
My recent Amiga 1200 purchase from another member on the site is giving me a little bit of grief.
I noticed that it was started with a red screen at time and would not boot.
I found that after reseating the roms chips it seems to be working as expected.

I started to check the system a bit more thoroughly and then noticed that I was only get 1mb of chipmen.
as this was my first 1200 i was sure I remember they came standard with 2MB.
I ran sysinfo and this confirmed that I only have 1MB
The system was sent from Italy to Australia which cost a small fortune. i would prefer to try and get the system working without sending it back and getting a refund from the seller.
Anyone have any ideas? I suspect one of the 256K modules could be dead and causing it to loose 512K or chip.
If it is one of the chips can they be replaced? If so would these work?
http://www.ebay.com/itm/251042002668?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649
Is there any diagnostic software to tell me what could be wrong?
I also got a Viper 1230 board from another member which a memory test is coming up with errors. i am not sure if this is the board or the amiga itself so i would like to the 1200 out and then see if this fixes my Viper1230.
Here are some pics of the mem screen shots.
Thanks everyone!
IMG_4531.jpg

IMG_4532.jpg


IMG_4535.jpg
 
Does it do the same without the accelerator?
 
bazzaq said:
Does it do the same without the accelerator?
Click to expand...

Agreed - try the 1200 without any extras plugged in.

Boot with a WB floppy and see what it says then.

Dave G :cool:
 
If disconnecting the accelerator doesn't change anything, the problem could either be the connection between the CPU and the memory chips which could be broken (corrosion or a screwdriver hitting the MB), a cut supply for a memory chip or it could also be a faulty memory chip.

I would probably first do a visual inspection, then try to ohm the address and datalines between the cpu and all the memory chips.
 
mamejay said:
Anyone have any ideas? I suspect one of the 256K modules could be dead and causing it to loose 512K or chip.
Click to expand...

Each chip RAM longword is spread over all four chips (8 bits each) so it's unlikely any chip has gone bad - in that case the whole RAM bank would be invalid.

Check continuity between pin #94 on the 68EC020 and pin #35 on Alice (A20 address line - decides which half of the 2 MB chip RAM is to be accessed), if Alice gets a stuck input on this pin then quite naturally only half the RAM will be visible/accessible.
 
Thanks everyone for your help.
The connection between pin 94 of the CPU and 35 of the alice is fine.
This happen without the accelerator installed and is booting up from a 2.05 WB install disk.
I cannot determine the Angus chip. All other are labeled with their names.
Which one chip is it?
 
sorry, verify connection from U20 budgie and ram, see page 7 of 27 pdf schematics, and verify r152a-f
 
Thanks for that. I did find the schematics that piacc64 mentioned.
I will check this.
If one of the traces is possibly broken from the budgie to R152A-F or from R152A-F to the ram modules, would this cause the symptoms that I currently have with my 1200?
 
Short answer: yes.

But you can also have a broken solder somewhere in the motherboard, as it probably was dropped by the (not) cautious postal system. Start from the centre of the motherboard in the direction of the RAM chips.

Retouch any solder joints that looks suspicious.
 
Ok. I did full checks on all the traces back to the ram and they all look good.
Now I decided to check a couple of other things. I attached a working hard drive (from an Amiga600) to the system and switched on the system. I was greeted with the insert WB disk screen.
I am thinking that there is too much wrong with this system now and for the money I paid it should have been working perfectly.

BTW the Alice chip is as follows
391010-01
8374-ALICE
4192 23

If that helps.
 
Iis this likely to be a microfracture of the solderpads on the CPU as is being discussed on the other thread about A600s and the ACA??
 
i dont know it was working here, horrible shipping can spoil a machine, i request mamejay to resend & refound everything ...sed but true, another amiga died or starting do it...
 
Thank you Tlosm. This was actually a birthday present to myself so I was a little depressed when it was not working properly.
If you have another that is tested I would be happy to get a replacement.
 
mamejay said:
Thank you Tlosm. This was actually a birthday present to myself so I was a little depressed when it was not working properly.
If you have another that is tested I would be happy to get a replacement.
Click to expand...

you know ;)

Sorry for this problems, dont warry you will have your birthday machine

ciao
Luigi
 
I would suggest exchanging mainboards only to save on postage ...
 
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