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Old 20 August 2019, 23:17   #21
KLund1
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I am terrible at reading schematics.
I pulled the CPU out and there was some gray from corrosion on pins 1-5, and 62-64. But no green. I cleaned those pins up. I used a bit of vinegar in the effected socket pins and around the battery area. I cleaned that up with some ISO. I tested continuity of CPU pins and the resistor array by the cpu with other near by solder points and further away, and they showed good. I also tested from CPU to some memory pics and got continuity.
I powered up and got about the same results, except I got a blue screen between the blinking green/red screen and the green bars blinking with black, with red lines.
So, from above I think we are looking at memory chips being bad?
None were warm after 5 minutes of power on. U548, U104, U103 were a little warm. Denise was warmer, as was Fat Lady.
Next tests?
Thanks
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Old 21 August 2019, 07:15   #22
demolition
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These are the color codes from the DiagROM documentation:
Code:
COLORCODES:

NOTE: Sometimes hardwareproblems might do that colorcodes are not visible. text is also dumped on serialport.

Green/Black		Detecting Chipmem
Green/Red		Detected Chipmemerrors
Green/Dark Green	No Memory detected
Red/White		CPU Bus Error
Red/Purple		Address Error
Red/Cyan		Illegal Instruction
Red/Yellow		Division By Zero
Red/Blue		Chk Instruction
Black/White		TrapV Instruction
Black/Purple		Privilege violation
Black/Cyan		Trace
Black/Yellow		Unimplemented Intruction
So if you get red lines while on the green/black screen, it should indicate that you have chipmem errors.
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Old 21 August 2019, 20:32   #23
KLund1
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That is very helpful. Thank you!
Yes probably memory. But there are a lot of soldered chips of memory. How to find the bad one(s) or is it one of the mem support chips. How to find out?
During this test, could I use a logic probe on a certain pin(s) on each mem chip. If it chirps good, if not, then a bad chip?
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Old 21 August 2019, 20:41   #24
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Not so easy unfortunately, but when you establish a serial connection so you can see the progress of the memory test, then perhaps you will be able to see identify which memory ICs are faulty if it is limited to one or a few bits over the entire memory span. For examply if bit 5 is the only faulty bit and it happens in the low memory region (<512kB), then you can identify which chip is responsible for that error in the schematic. So when you are able to see the detailed results of the memory test, then you can take it from there.

My A2000 board has 32 DRAM chips and I found that 22 of them were faulty, so that was quite excessive.. I imagine some faulty PSU in the past could be responsible since so many chips were broken, or perhaps someone shorted the 12V and 5V supply lines which caused the 5V supply voltage to increase.
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Old 21 August 2019, 21:16   #25
KLund1
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Thanks
Ordered a cable and installed puTTY. I checked my memory stock and I have no 32K chips.
Could you post a link to the proper mem to buy?
Also While I wait, I might as well double check traces with a schematic. It is a pain to figure them out but better to be sure.
I was not able to find a B2000 Rev 4.4 (not 4.5 as post above, sorry) schematic.
Where might I find one online?
All this help appreciated!
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Old 21 August 2019, 22:33   #26
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This service manual has schematics for A2000 rev 4.4:
http://www.retro-commodore.eu/amiga-tech/
2nd line, item in the middle.

The schematic with the DRAM chips are found on page 66 in the pdf. And yes it is a pain to go through that many traces, however just be happy that the bus is not 256 bit wide.

I found that the RAM chips are not as easy to find as they have not been used in as many products. They are 256k x 1 bit and here are some names you can look for:
33256
41256
TMS4256
21256
MCM6256

A friend had some that I could get so I didn't have to buy some fortunately.
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Old Yesterday, 00:25   #27
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If you don't mind the long delivery times, you can get the 41256 chips from China fairly cheaply via eBay. I bought a pile of them to fix an A2052 RAM card recently.

These look like a good fit:

https://www.ebay.com/itm/50pcs-MN412...kAAOSwLzZc44ZW

You would be best putting in sockets for them so you can pop the new ones in easily
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Old Yesterday, 03:06   #28
KLund1
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Quote:
Originally Posted by demolition View Post

I found that the RAM chips are not as easy to find as they have not been used in as many products. They are 256k x 1 bit and here are some names you can look for:
33256
41256
TMS4256
21256
MCM6256

I thought I was looking for 32K ram chips.
I have lots of 33256, 41256, 21256 chips, most a -12 some -15. are those speeds ok?
Thanks for the schematic link.
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Old Yesterday, 03:46   #29
Vypr
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Quote:
Originally Posted by KLund1 View Post
I thought I was looking for 32K ram chips.
I have lots of 33256, 41256, 21256 chips, most a -12 some -15. are those speeds ok?
Thanks for the schematic link.
The lower the number the better so the 12's would be ideal if you have enough.. I have all 41256-12s in my A2052. It originally had 15's installed but the A2052 got a reputation for flakiness with those speeds.
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Old Yesterday, 06:19   #30
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Before you de-solder a bunch of RAM chips you might want to try jumper J101 which will change the addressing for the chimp mem from 1meg chip to 512k chip 512k fast. If that makes a difference it might tell you if the problem is in the first or second half of the memory.

Also a bad Agnus can show up as chip mem problems - swapping for a known good Agnus may help.
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Old Yesterday, 06:34   #31
demolition
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Quote:
Originally Posted by KLund1 View Post
I thought I was looking for 32K ram chips.
I have lots of 33256, 41256, 21256 chips, most a -12 some -15. are those speeds ok?
Yes, 256kbit is 32kB so you are correct on that. RAM chips are just always specified in number of bits or words and not bytes (unless the word size happens to be 1 byte).

-15 (150ns) is what is stated in the schematic so it should be fast enough. It is running synchronously so using faster chips will not improve anything (doesn't hurt though).

You might not need it, but I found this page that list the variants from most manufacturers:
http://www.citylan.it/wiki/index.php/DRAM_256k_x_1
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