VOGONS

IBM 5170 Type 3 MB stuck at post code 09

Topic actions

First post, by mita

Posted on 
User metadata
Rank Newbie
Rank
Newbie

Hi,

I try to repair an 5170 Type3 MB but I need help, suggestion which direction is worth to pursue further in the repair process.

MB stops at 09 post code indicating Bios checksum error.

I checked the following:
- Voltages are in spec
- mechanical status is ok, no damaged traces, no corrosion
- Original TMM23256 HI, LO Proms are removed, contact cleaned
- CPU is removed, contact cleaned
- Tried to read and check the content of the TMM23256 with RT809H but this chip is not in the database. I tried to read as M27c256 as 32k EPROM but the programmed indicated pin contact errors therefore I left this track
- Downloaded the both bios from https://minuszerodegrees.net/bios/bios.htm - 5170 section type 3 bios based on the printing on the original bios (62x820,62x821), programmed to m27c256 eprom. The result is the same.
- I found some discrepancy concerning the bios checksums on both variation of the bioses. The bios archives contain a text file which gives information about the bios files and its checksum values. I have checked the checksum values with HxD program and got different 8 bit checksum values computed and the values at the last byte of the BIOS files AND the checksum given at the text description. On the other hand the sum of the last bytes of the two bioses gives zero therefore it should be right. In spite of this the MB stuck at 09 post code.
- Checked all the pins of the two BIOS with logic probe. All address lines and datalines, OE,CE is moving for about a second and stop moving after that. Based on this I would close out a stuck data, address or control line
- Removing the drams has no effect, the bios never reach the initialization - post 13- of the drams.
- One more option: maybe the 09 code is a bit misleading. Maybe the bios checksum is ok and the BIOS is running further but stuck at the point before reaching the next post codes. Does anybody know which is the next post code after 09?

I would appreciate any help to figure out what would the potential cause of the problem and what would be worth to check further. I am not familiar with bios checksums, maybe the solution is quite simple. I am planning to use a 5170 Diagnostic bios but I have to look for the right CGA display and display card.

Reply 1 of 4, by douglar

Posted on 
User metadata
Rank l33t
Rank
l33t

Is this helpful? https://www.minuszerodegrees.net/5170/post_er … _post_codes.htm

All three versions of the BIOS are the same here.

09 Refresh bit - Verify that 'refresh bit' is toggling. See note 9.
Note 9 Verify that channel 1 of the 8254 timer chip is periodically generating a 'RAM refresh request'.
So what is being looked at is simply something that triggers a RAM refresh cycle.
That is not the same as verifying that RAM refreshing is actually occuring.

0A 8042/8742 keybd controller - Buffers See note 8
Note 8 1. If output buffer full, flush it. 2. If input buffer full, and 100 ms later is still full, halt the CPU.

Reply 2 of 4, by mita

Posted on 
User metadata
Rank Newbie
Rank
Newbie

Thank you for your quick reply! It is a big help, I missed this post section on the minuszerodegrees.net site.
Checked the timer IC with logic probe. All the three channel's clock, gate and output are active until the post reach the 09. After that all the activity dissapeared.
Checked the DRAM CAS, RAS signals. These show a quick burst of activity until post 09. Tha address and data pins are moving as well, no stuck lines detected.
Checked the 8042 as well. The CE, RD, WR signals are active until the 09 post.
My next try will be a test with Supersoft diag rom, but eeproms shold be sourced for that.

Reply 3 of 4, by Deunan

Posted on 
User metadata
Rank l33t
Rank
l33t

Is this machine still using DMA controller to steal CPU cycles for DRAM refresh? If the mobo has 2 DMACs I would swap them places to see if that does anything useful. Assuming it's not integrated into chipset already, I have very little experience with original IBM PCs.

Reply 4 of 4, by mita

Posted on 
User metadata
Rank Newbie
Rank
Newbie
Deunan wrote on Yesterday, 20:26:

Is this machine still using DMA controller to steal CPU cycles for DRAM refresh? If the mobo has 2 DMACs I would swap them places to see if that does anything useful. Assuming it's not integrated into chipset already, I have very little experience with original IBM PCs.

Yes it has two 8237 DMA controllers. Unfortunately they are soldered directly, swapping would be a painfull job.

Go to top of page Go to top of page
Back to General Old Hardware
Close window
Close window