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stargazerf3a

XEgs Rom Error Test

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Hello to all members ,

Yesterday i had a lucky find outside the trash, a XEGS always wanted an 8 bit computer and voila but,
When i power it up it goes to memory test which shows me two red squares for rom. Every ram square (40 of them) are passing the test ok.
Already i tried to reseat the only socketed chips Rom and GTIA also used contact cleaner but the same happens.
Also i've removed every capacitor and measure it with a capacitometer and every single one is ok.
I am asking you is there a way to bypass the self test maybe put 5Volts to pin 6 of mmu?
Is there anythink else i can do ? I have a full electronic lab except a logic probe.
Thank you for your time...

Edited by stargazerf3a

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Just replace the two chip ram, available from best electronics. I can almost guarantee you they are MT ( Micron Technology ) ram. The ram won't reset; it acts like statics ram, or just bits of it won't work at all.. The motherboards are cheap so take care in desoldering them because it's easy to pull up a trace and pad. I use a Hakko. Can you post a pic of your power supply please?

Edited by Paul Westphal

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And Rom shows as 2OM maybe this is a clue?

It is in my book, sure enough. Borderline timing issue

that is effecting how both rom is read and ram is

written/read back. I would attempt to piggyback a

74HCT08 logic chip onto the 74LS08 chip you already

have to see if that makes a very noticeable difference.

 

Be sure to squeeze the legs of the addon chip so that

each leg makes good contact and you might want to

be squeezing it and moving it ever so slightly to

see if this might induce better contact and make

the display straighten up.

 

Chances that your ram and rom are both bad at the

same time are slight. Your display is based entirely

in ram and it's wrong with a single replacement 2om.

Rom isn't reading correctly at all and yet most of

the code is good? Rom usually makes a real mess of

the bed when it goes bad. All of that running code

is 99.999% good and it all comes from rom. Can't be

both ways, but it sure can have a weak clock causing

bad timing issues which the HCT08 will straighten out.

We can hope.

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Thank you guys for your answers ,

My iron is of weller brand

My power adapter is a sony ericsson mobile phone 5Volt adapter :)

So first i will replace 74ls08 chip and then memmory chips

Also question how do i burn the rom to the existing chip?

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You can’t burn a rom to the existing mask rom chip. The best option for you is probably to order a new rom. Alternately, if you have an EPROM burner and blank EPROM chip of the correct type, then you’d be able to burn a new one.

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You can’t burn a rom to the existing mask rom chip. The best option for you is probably to order a new rom. Alternately, if you have an EPROM burner and blank EPROM chip of the correct type, then you’d be able to burn a new one.

I suppose a compatible eeprom is out of the question?

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I suppose a compatible eeprom is out of the question?

Not normally done is all, I don't have a recommendation

either. But you'll need a 27256 equivalent, eprom

speed should be rather slow 200ns, don't know about

eeprom speed though.

 

http://atariage.com/forums/topic/259483-xegs-game-rom/?do=findComment&comment=3639787

 

It's likely to be the ROM but ram is lower pin count.

Will need a programmer for eeprom too but there are

some good cheap USB universal programmers out there

on eBay for example. $40, I'd get one myself but I

already have such a version in parallel printer port

style made a bit before USB took over like it has.

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Not normally done is all, I don't have a recommendation

either. But you'll need a 27256 equivalent, eprom

speed should be rather slow 200ns, don't know about

eeprom speed though.

 

http://atariage.com/forums/topic/259483-xegs-game-rom/?do=findComment&comment=3639787

 

It's likely to be the ROM but ram is lower pin count.

Will need a programmer for eeprom too but there are

some good cheap USB universal programmers out there

on eBay for example. $40, I'd get one myself but I

already have such a version in parallel printer port

style made a bit before USB took over like it has.

This one could do the job? https://www.ebay.co.uk/itm/USB-Universal-Programmer-Support-13000-ICs-EPROM-FLASH-MCU-PIC-7pcs-Adapters/111631739482?epid=1588690105&hash=item19fdc52a5a:g:EU0AAOSw8-tWT92U

 

And also which eprom will i need?

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Yes it will. A bit spendy but you get a bunch of

programming sockets for the small square packages if

that's something you wanted.

 

https://www.ebay.co.uk/itm/Eprom-TMS-27C256-20JL-4-Pieces-IC-TEXAS-INSTRUMENT/232623130991

 

Download the datasheet for it to find speed rating

of 200ns represented by the -20JL part of the number.

10F1 short for 100ns

12F1 short for 120ns

and many other 'codes' used and each one should be

looked up in it's own datasheet only. This is legwork

and it should be done.

 

I find that my 8bits appreciate 200ns speed OS ROMS.

Faster ones have been flaky - sort of like what you

have right now (!!!!!). So above, you buy 4 when you

only need one because the slow ones aren't so popular

anymore? I would here all day long and consider it

an investment. Unless you can find one at 200ns at a

reasonable price by spending a bit more time at it

than my measly couple of minutes.

 

Same programmer will handle eeproms and the number

there is 28256, but again I don't know what speed

would be best there. Commercial usable eproms are

working but not same speed as eproms as I know the

game to be played - don't understand that, haven't

gone there so I can't suggest a thing except you

are on your own.

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Hello guys,

 

With your help i was able to resurrect my atari xegs i've also made a sio2pc cable and now i am enjoying 8bit goodness

All it took was a tl866 programmer and a blank eprom

 

THANK YOU GUYS

Edited by stargazerf3a
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Hello to all members ,

 

Yesterday i had a lucky find outside the trash, a XEGS always wanted an 8 bit computer and voila but,

 

 

Oh do share the story.. I love these stories.

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