(Topic ID: 254084)

No blanking, system 6. Using Pincoders ROM's to troubleshoot

By Brewchap

4 years ago

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32 posts
4 Pinsiders participating
Latest reply 4 years ago by Brewchap
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OP
Quoted from Brewchap:
This system 6 MPU board was a working board until I pulled IC7 to test on another board. I replaced the 74041N at IC7 and with Pincoder's ROM 1a I should get an alternate flashing of the top and bottom LEDs. Now all that I get is the flash of both lights, then the top light stays on.

Your CPU chip is crashing. Either because it's flakey, or more likely, because one or more of the ROM sockets is bad. Perhaps just a weak solder joint somewhere on the MPU board.. the VMA signal is generated by IC1 whenever it places a Valid Memory Address on the address bus. If it stops doing that then it has crashed.

Hi sorry for the delay I'll try to answer tommorow

OP
Quoted from Brewchap:
Wanted to let you know that test ROM 3 will fail if you have a NVRAM installed instead of a 5101.
On an system 4 fail the bottom light will light up.
On an system 6 fail both lights will light up.

This is certainly odd behavior. The RAM and CMOS tests use the same code, just different parameters. Also, the output of the test is to light either LED, not both so I have to assume that when you see both lights it's because the test isnt booting at all. The LEDs both light upon power up and the first thing the test does is shut them off. It then proceeds with the test and displays the results..

As for the NVRAM, it shouldn't make a difference. However, if the NVRAM chip does not have a response time at least as fast as a 5101 then its possible the test will fail. Can you send me a link to the product you are using?

What results do you get when you run 01a-leds on the system 4 and system 6 boards? They should both boot and run. If not you may have to go back to checking solder joints, sockets, etc.

How do you know the boards are booting the williams roms on the bench?

Now that you have swapped the power supply could you please run the 03-cmos tests again with each of those NVRAM chips?

Also, is IC7's output to the blanking timer good now?

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