Repair needed

[xdslx]

I bought an atari 800xl, starts with memtest. I replaced thr OS B rom but problem exists here is a video of it . I hope someone can solve the issue. C014806C (U8) and DMPAL17L8NC (U3) is getting a little hot , maybe thats normal I dont know.Rest of the chips are cool.

 

https://youtu.be/fcav12r40TE

[TangentAudio]

First step (and always wise with vintage computers as a general rule) - check the power supply output voltage with a voltmeter. Depending on the particular power supply you have, it may have failed in a way that is damaging the machine. Some of the XL/XE supplies have been known to fail and output over 5V which can damage many parts, but RAM seems to be the most susceptible.

[xdslx]

I have tried it with my old adapter which is exactly 5.0v and with the new one with 5.1v. Result is same.

[TangentAudio]

Fully socketed 800XL? Have you gently removed/reinserted every chip? Over time the pin/socket connections sometimes develop poor contact, and reseating the chips can help.

[Rybags]

U8 is the CPU, U3 the MMU. The Self Test is at least starting so the CPU is likely OK, the MMU as well.

 

I suspect bad Ram or a Ram selection problem. What's going onscreen suggests that. For the memory test, the Display List is within the SelfTest Rom so isn't corrupted.

The text "MEMORY TEST" as well as the words ROM, RAM are copied to Ram as well as the pass/fail dots.

The text at the bottom is contained in Rom too, so isn't corrupted.

 

Warmer than usual Ram chip/s can indicate they're bad. But you might need to let it run a few minutes first.

[xdslx]

board is fully unsocketed . I let it run few minutes and cpu is the hottest. U3 and U29 is a little warm but not hot as U8.It writes ROM on screen but I cannot see it write RAM on the screen , as I remember it must be written on screen too. I wonder what R38 does which can move like a wheel. And the new adapter which is 5.1V 2.5A which shouldnt get any hot , gets a little hot after 5 mins . Attached is a picture which it gets stuck before I replaced the OS rom chip. I am not sure to spend more time on this.or not.

Edited May 12, 2017 by xdslx

[TangentAudio]

R38 is the color adjustment, shouldn't have any effect on your memory issues.

[russg]

board is fully unsocketed . I let it run few minutes and cpu is the hottest. U3 and U29 is a little warm but not hot as U8.It writes ROM on screen but I cannot see it write RAM on the screen , as I remember it must be written on screen too. I wonder what R38 does which can move like a wheel. And the new adapter which is 5.1V 2.5A which shouldnt get any hot , gets a little hot after 5 mins . Attached is a picture which it gets stuck before I replaced the OS rom chip. I am not sure to spend more time on this.or not.

It seems that there is no BASIC. A normal startup of a 800XL is to go to the READY prompt.

If you could hook a disk drive or APE device with DOS, you could type DOS commands. If

you got to a normal command line, you could type BASIC ON, but I suspect it wouldn't

enter BASIC.

Are you sure you replaced the OS ROM, and not the BASIC ROM place?

Edited May 12, 2017 by russg

[Rybags]

The XL does an inversion and store $FF then $00 as part of the powerup memory test and if any of that fails will go straight to Memory Test.

The only way around it is fix the problem or insert a diagnostic mode cartridge (Salt, Asteroids, Star Raiders, some other games).

[xdslx]

I replaced the one under the basic chip.removed the old one ,socketed the motherboard then put this ( http://m.ebay.com/itm/NEW-Atari-computer-400-800-XL-130-XE-Operating-System-Rom-IC-Chip-C061598B-01-/162099925963?hash=item25bde893cb%3Ag%3AQG8AAOSwbYZXWyCE&_trkparms=pageci%253Aa1b10856-37a3-11e7-bbee-74dbd18040b2%257Cparentrq%253A00730ce215c0ab4506665d82ffff3810%257Ciid%253A2) one.

 

Should I have replaced the Basic chip ?

Edited May 13, 2017 by xdslx

[xdslx]

Unfortunately I do not have any of the carts , but I have the equipmant to make a UnoCart. Can I test it with Unocart ?

[russg]

I replaced the one under the basic chip.removed the old one ,socketed the motherboard then put this ( http://m.ebay.com/itm/NEW-Atari-computer-400-800-XL-130-XE-Operating-System-Rom-IC-Chip-C061598B-01-/162099925963?hash=item25bde893cb%3Ag%3AQG8AAOSwbYZXWyCE&_trkparms=pageci%253Aa1b10856-37a3-11e7-bbee-74dbd18040b2%257Cparentrq%253A00730ce215c0ab4506665d82ffff3810%257Ciid%253A2) one.

 

Should I have replaced the Basic chip ?

You replaced the OS ROM. The BASIC ROM above the OS doesn't seem to be working because

you go straight to the self test instead of BASIC.

If you could attach a SIO2PC/APE or a real floppy drive and boot DOS, you could enter a BASIC ON command.

If you could get a DOS, you could load a file BASIC. You might be able to remove the BASIC chip and still

be able to boot to a DOS.

Something is wrong, I'm not sure what.

 

If you take the BASIC out, it should go

to the mem test. Try taking BASIC ROM out and see if a good mem test comes up.

Edited May 13, 2017 by russg

[Kyle22]

You can remove the BASIC ROM with no problem. Everything will work fine, just no built-in BASIC. If you can find a 68766 EPROM, it is a direct drop-in for the BASIC chip.

[xdslx]

Ok thank you.I will desolder the basic chip.But I think Basic chip seems to be the second ROM on self test.so it should stuck if I take it out.service manual says U5 or U2 is damaged if it goes to self test upon boot.I dont want to solder or desolder the motherboard more without being sure what the problem is.

[Rybags]

Fairly sure Basic isn't involved in the Rom test, the OS Roms have checksums which can be validated by Self Test or 3rd party routine but Basic isn't essential for system operation so there's no internal checksum, and not really needed since there's only the 3 well known revisions.

 

IMO, taking the Basic Rom out will make no difference to your problem. I think you should be concentrating on the Ram chips and memory select logic.

Edited May 13, 2017 by Rybags

[xdslx]

Rybags , saying " memory select logic " , do you mean U3 and " memory management unit " in another words ?

[russg]

Rybags , saying " memory select logic " , do you mean U3 and " memory management unit " in another words ?

A common problem is MT drams. Check your drams, the memory chips on the left. If they are MT

that's probably where your problem is.

[Rybags]

For any 8-bit machine before they started putting the Freddie chip in the memory select logic is somewhat more complex.

 

Look at the 800XL schematic involving Ram vs the one for 65XE to get some idea.

You have the delay line (U29) then the 74LS158 pair (U26, U27) which buffer the address to produce Row/Column.

 

WIth Freddie equipped machines those points of failure and more are taken away (OK, so Freddie in itself can be a point of failure but doing all those functions in one chip is a whole lot more reliable).

 

But anyway, it comes down to finding the failed component/s. Being fully socketed makes it a right pain, so I suppose the logical way would be to chase it down in order of likelihood.

If any Ram chips are stamped "MT" then they're automatic prime suspects.

As for the remainder, it's a lot easier when you have a companion machine where you can swap chips back and forth to help id the bad ones.

[xdslx]

I have my other working 800 xl from 1986 , with never opened chasis.But I dont want to open it.

So , 4 rams begining on the top of the row are " 411 MT 4264-15 " , below them are 4 rams are " 445 MT 4264-15 USA "

So , when replacing , shall I buy 411 ones or 445 ones seperately or any 8 piece of them is ok ?

Edited May 14, 2017 by xdslx

[BillC]

I have my other working 800 xl from 1986 , with never opened chasis.But I dont want to open it.

So , 4 rams begining on the top of the row are " 411 MT 4264-15 " , below them are 4 rams are " 445 MT 4264-15 USA "

So , when replacing , shall I buy 411 ones or 445 ones seperately or any 8 piece of them is ok ?

I believe the '411' and '445' are just production date codes(11th and 45th week of 1984).

41256 chips can be used instead of 4164, and are often less expensive.

[xdslx]

41256 are 256 k am I wrong ? are you sure they work without any mod ? and somewhere I read that rams shouldnt be under 12 ns . so I should buy 41256 rams with 12ns or more latency , to be sure ?

[Stefan Both]

Even in the C64 Scene,

the MT Rams are well known

for its unreliability.

You need Rams with 150 ns or less.

Believe it or not

 

Below is a List with Rams,

compatible with the C64.

It should met the needs of a XL also.

 

TMS4164-xx (TI)

D4164-xx (NEC)

M3764-xx (OKI)

5K4164ANP-xx (Mitsubishi)

MCM6665APxx (Motorola)

MCM6665BPxx (Motorola)

HM4864P-xx (Hitachi)

KM4164A-xx (Samsung)

TMM4164P-xx (Toshiba)

MB8264A-xx (Fujitsu)

MT4264-xx (Micron Technology)

LH2164-xx (SHARP)

MN4164P (Matsushita)

U2164D (DDR)

HY51C64 (Hynix)

P2164B-xx (INTeL)

 

Stefan

 

Err have I already mentioned, NOT to

use MT Rams

Edited May 14, 2017 by Stefan Both

[xdslx]

thank you all who helped me. I will be back after the replacement...

[BillC]

41256 are 256 k am I wrong ? are you sure they work without any mod ? and somewhere I read that rams shouldnt be under 12 ns . so I should buy 41256 rams with 12ns or more latency , to be sure ?

41256 DRAM were used with 256kB RAM upgrades(RamboXL/Wizztronics/Newell/generic).

 

The only significant difference is that the 41256 have an extra address line, they are backward compatible with 4164 chips if this is grounded.

[RodCastler]

I'd assume bad RAM considering the fact that the system jumps straight to selftest but leaving that aside,I'd be concerned about the graphics on the selftest program itself: they seem so odd. I'm curious about what the selftest looks like after you replaced the ROM chip....

Edited May 15, 2017 by RodCastler