5. SYS-Check II
Here´s a somewhat abbreviated description. I hope I´ve found the right words and the text is translated reasonably understandable.
Sorry for bad grammar and mistakes; I didn´t have much experience in speaking englisch.
I can´t add pictures (got an error-message); for the missing pics please have a look at the ABBUC-Forum
Project "Sys - Check II" is designed to allow preliminary diagnoses on faulty devices without opening an Atari XL or XE and to simplify troubleshooting.
Sys-Check II (the following simple "Sys-Check") is a pcb fitting to the XEs ECI and the XLs PBI. When using PBI either +5V must be applied to pin 47/48 or a cable located on the pcb is inserted into pin 7 of the joystick port 2 (as known from the Turbo-Freezer).
For normal operation as a diagnostic card, both DIP switches must be in the "OFF" position, ie show towards the right edge of the board.
Sys - check can also be used with an Atari 600XL , but it must be upgraded to 64K. For computers that have less than 64 Kbytes of main memory , Sys-Check will always report an error.
Start up Sys-Check
For the proper function, a possibly inserted module must be removed (the built-in BASIC is always hidden). For computers with built-in SDX , Flashmodules or other enhancements of this kind , they must be completely disabled or removed (if possible).
After switching on the computer with Sys-Check plugged in, memory test starts immediately. This looks as follows:
First 2 KByte RAM are checked in one step:
If Sys-Check reached this point you can say that...
- CPU, ANTIC and GTIA working correct
- No short at the Data- or adressbus
- Supply voltage seems to be stable
If this step is sucessfully done, the display switches to 256 Byte-steps:
RAM between $0800 and $BFFF is cheked per page. Subsequently, the upper 16K (the area „below the operating system“) are checked.
To test this memory, video output is disabled, otherwise it would result in graphical errors. Thus, the user sees that the test is still working, a few colorful patterns are shown, as is known from unpackers:
If this is also gone through properly , hopefully the positive message appears that the memory is ok:
Now, Sys-Check is waiting for pressing START - or pressing the fire button of joystick 1 if no keyboard is connected. (Therefore, the +5V should be taken from joystick port 2 )
For running the memory test, the mainboard must not be completely equipped with all integrated circuits: The POKEY may be missing, the PIA also. Operating system and BASIC-ROM can be removed. Even without a single RAM on the mainboard the the test will run, but, of course, report errors.
For the following test - if the operating system ROM is working properly - the PIA is required. Checksums of the OS calculated and compared with the checksum stored in the ROM - just the same the well-known self-test does. Here only two output options are possible:
Checksum okay – everything´s fine.
If checksum doesn´t match, this could have different reasons: perhaps the OS ROM (or EPROM) is defective, not plugged in or there is a patched OS version on it with disabled self-test and the checksum was not adjusted correctly. Good patches (as Hias' High Speed SIO patch) should run.
In the many years I spent in fixing XL/XE, I found several broken OS-ROMs! This is not as rare as some might think. A non-starting Computer must therefore not always be a mistake of the RAM, but also like the OS ROM. Sys-Check recognizes this reliable. At this point, you can´t do much more except re-START (or fire button of joystick 1) in order to re-start the test from the beginning. This can be quite useful if you suspect a temperature-dependent error.
Detection of defective RAM
A computer with defective memory is easy to detect for the experienced Atarians. Who has an old 800 XL motherboard with the Rams are socketed, tests gradually all RAMs by and usually has relatively quickly found the or the "guilty" ones.
Unfortunately, newer XL and XE generally have no socketed RAM, therefore troubleshooting is more difficult. Although build-in selftest sometimes starts, but shows endless memory errors - useless for the user. Due to the 2D matrix of DRAMs (addressed in columns and rows), we must have the exact address of the defective Bit(s) to calculate what memory chip has a quirk. Here Sys-check comes into play: if Sys-Check detects defective RAM, this is displayed as follows :
This example shows a defective DRAM chip containing data bit 6 (01000000). Sys-Check shows in an easy-to-understand way which DRAM on the board has to be replaced. The chip number (Uxx) agrees with the respective board and match as well with the position of the chip. There are four columns showing the location of the DRAM which are easily distinguish to the corresponding Atari.
column 1 „800 XL“
The most prevalent version (PAL as well as NTSC) of the Atari 800 XL. Easy to recognize: it has five large chips with 40 pins.
column 2 „800 XLF“
This version of the Atari 800 XL motherboard is also easy to recognize: it contains six large chips with 40 pins. It is called "ROSE"-motherboard with the Freddie-chip , which is otherwise found in the XEs and the XEGS only.
column 3 „XE 8x4164“
In this column, defective memory with an Atari 800 XE or XE 130 which with 8 DRAM modules 4164 ( Atari 800 XE ) or with 16 DRAM modules 4164 ( Atari 130 XE ) are equipped, are shown. In these models, the 8 blocks to the left are the DRAMs , which are responsible for the main memory. The right of it are the 800 XE unequipped and the 130 XE for additional storage. For the testing of the additional memory there are enough good programs , so Sys-Check doesn´t check this not yet.
column 4 „XE 2x41464“
The last column is for the Atari XE board versions, which only contains 2 or 4 DRAMs 41464 on it. The 130 XE with this mainboard has four chips , the 800 XE two chips. For the main memory, always the upper two chips are of note. Since a DRAM type 41464 stores four bits at a time, an error in bit 0..3 always marks the upper (U9), an error in bit 4..7 always the lower RAM (U10).
If several bits are defective, it is also recognized by Sys-check and multiple defective chips are shown:
In this example, the data bits 0 and 3 are defective. This example also shows that the Atari 800 XL with Freddie and the Atari XE with 8 or 16 DRAMs , although have an identical U-name, but not the same bits of the same respective positions of DRAMs. Again, press START or the fire button of the joystick in port one to restart the test.
Now "just" heat up the soldering iron, exchange the marked chips and hope that it's.(in most cases this should be the case).
What Sys-check can not
Spells; because of a lack of power
If there are any short circuits, no clock is generated, MMU, CPU, ANTIC or GTIA is defective, then Sys-Check doesn´t work. It is not a panacea. But in practice, 90% of all defective Ataris due to broken memory or ROM. Troubleshooting should therefore be quite shorten dramatically in many cases by Sys-Check.
In rare cases, it may happen that all bits maked by Sys-Check as defective. Or in case of multiple starts Sys-Check finds other defects every time. In such a case, only the classic replacing methode will help. Usually, this is due to a DRAM which short circuits to the address lines of the RAM (MAD0..7). Also, such an error due to a defective Freddie or another components involved to RAM-control (the two 74LS158 , 74LS51 , the Delay Line IC , etc. ).
It should then are classic looking with an oscilloscope or just blindly replaced. In general, of course, should the usual instructions are followed. In case of defective XL or XE are these restore in case of doubt to its original state. In general, should the board are only fully developed and tested outside of the housing. a Visual inspection on charred strip conductors etc. is also mandatory.
If Sys-Check doesn´t run
… there could be different reasons:
- CPU, ANTIC, GTIA, MMU or another, important chip is damaged.
- problems with the power supply
- Contacts of PBI or ECI / module bay ( XE ) are dirty or corroded
When the board was removed from the housing , especially the XL PBI should be cleaned. Use an eraser to clean both(!) sides of the PBI properly. Then remove the eraser residues with a dry cloth.
When there is any solder at the contacts of the PBI , the corresponding contacts are to clean and remove the solder with a desoldering pump or solderwick. It is important here that all contacts have the same " level " so that the contacts of the Sys-Check have a secure connection.
The XE provides cleaning with compressed air , vacuum cleaner etc..
Are clear skid marks on the contact tongues seen emerize them carefully with a nail file or fine, folded sandpaper.
What will be next ?
Sys -Check offers many expansion options , I gradually will implement. Unfortunately, not enough time anymore to install delicacies. But my goal should be to rebuild all the tests that the ATARI´s CPS SALT test module offers. A few of the upcoming features:
- Test of joystick ports
- Test of extended RAM
- Test on GTIA error
- And much more...
Obduktion von Sys-Check
Sys-Check is built up deliberately simple and easy to solder. No SMD components used and all components are mounted to each other by a wide gap, that also not very experienced hobbyists should be able to populate their Sys-Check pcb.
Edited by Sleepy, Wed Sep 3, 2014 1:06 PM.