I got on on ebay, and of course it's dead.
It will not post. I looked inside at the main board and there is an empty >socket U16. I think this is an eprom. If any one can confirm my suspicion >that would be very helpful.
I did find a complete schematic for the printer, and am planning a debug >session this weekend.
Here is the situation now.
The power supplies all check out.
The clock circuit is working. (8.08mhz)
The reset circuit seems to be working.
The processor is dead. No activity at all.
I tried to find documentation for the TMS 7041 chip.
No luck there.
I tried to find documentation for the TMS 7041 chip.
Here is the situation now.A quick read of the databook indicates that the CPU clock is suppose to be 2.5 MHz across pins 17,18. If the 8 Mhz is at the CPU clock pins, that is high. For processors of that era I would do o/c experiments and they usually fell apart around 105% of
The power supplies all check out.
The clock circuit is working. (8.08mhz)
The reset circuit seems to be working.
The processor is dead. No activity at all.
I tried to find documentation for the TMS 7041 chip.
No luck there.
Kinda stuck at this point.
jc
A quick read of the databook indicates that the CPU clock is suppose to be = >2.5 MHz across pins 17,18. If the 8 Mhz is at the CPU clock pins, that is = >high.
Page 4-27 lists the max clockin to be 10.2 mhz. The CPU has an internal divide byI looked in the data book to see if the clk had a divider ckt but didn't find any. If you found one then ya, 8MHz would put it into specs. U16 is the processor? or the ROM? I am not at all familar with the thing you are working on.
4 circuit. I guess the 8mhz clock is o.k.
Probing with a scope.
I see pin13 has (INT1) 76hz. It seems to conform to the description in the terminal manual.
No data buss or address buss action at all. The MC bit is 0, as documented in the terminal
manual, for full expansion mode.
Reset is a 1. I blipped it with a ground, and did not see any changes at all.
Here is an interesting point. The CLOCKOUT pin 2 is a . No clock. This may be set by the boot
ROM.
I quickly gleaned that on startup the CPU does a data fetch at FFFF,FFFE
for boot sequence and yet you dont see any bus activity?
My next official step will be to replace the power supply caps.
I doubt that this is the primary problem, but its not that hard to do.
Well, I am seeing a bit of racket on the +5 rail. So, a few bucks for caps seemsClosing out this discussion.
in order.
Bypass caps eh? I'll have a go at them also, the the power supply caps come in.
jc
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