Electronics > Repair
What more i can do?
drhex:
Data and address are shared buses connected from the CPU to all chips providing/getting data. The CE signals (amongst others) control, who owns the bus at a given moment. So make sure that there is continuity on all lines between CPU and EPROMs/RAM at least.
Harry_22:
--- Quote from: 222Lab_Test222 on December 06, 2024, 01:56:52 pm ---What shall we do next?
Where are we heading towards, its all dark ahead, we need some candles or some lights.
--- End quote ---
You are not the only one with your problem. There is also my son this week.
Sorry for being off-topic, but I couldn’t even upgrade his computer with the new ROG STRIX Z790-H mother and 8GHz memory. The motherboard can update the BIOS without a processor and memory, do prestart diagnosis. The only thing it couldn’t do was simply come to an agreement with the monitor. It just turned on the white VGA LED and remain silent.
Today we solved this problem by simply connecting another monitor for the first start. Everything works now but it cost me another set of DDR5 memory.
Anyway there are more benefits. Thanks to remote work my son can rebuild his own computer now.
You were also able to learn something, right?
Harry_22:
Could you check that the address and data of the processor and EPROM match.
As you can see on the picture CPU address bus consist of two components: 30 address lines (A2-A31) and 4 byte enable lines (BE0#-BE3#)
I cannot understand why is start instruction fetching begins from 3FFF8H.
PS
I would like to say that it was not in vain that you film the data.
I found something.
fzabkar:
The slow EPROM would at some time be unpacked into RAM, especially when MS-DOS boots. That necessitates remapping the address lines by the chipset. Perhaps you are seeing the result of remapping?
asis:
Hello,
In my practice, I once encountered a similar problem while repairing printing equipment
VEB Polygraph Buchbindereimaschinenwerke Leipzig -
VEM NUMERIK "KARL MARX" Karl-Marx-Stadt, a country that no longer exists - GDR.
In practice, I had to reverse engineer all the boards, including the six-layer CPU board (U880 - Z80).
EPROM was made on UV U2716 24 pieces (MC2716)
During the repair, dumps were taken from all EPROMs.
And, the programmer that I recommended to you (Advantech LabTool 48) allows you to do final verification of the EPROM contents, using a check when increasing and decreasing the power supply from the nominal value.
As it turned out, - a very effective verification method that identifies vulnerable UV ROM cells.
-
And so.
I would like to offer you a method that involves supplying additional power to the PCB in the +5V circuit with an acceptable excess of +5.5V, in parallel with the already present - from the standard PSU.
If, of course, you have a reliable laboratory power supply.
The goal is to provoke a change in the situation or reaction, including TTL and everything else.
In this case, you can manipulate the "virtual RESET button" that @Harry_22 talked about.
-
In fact, you do not risk anything if you do everything consciously and carefully.
If there is a result, then a further strategy can be developed.
@222Lab_Test222 I do not insist on anything.
It's up to you.
Good luck.
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