Defender help! Resetting issue

andy251203

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Just got a defender the other day. It was in really good shape, very clean. Plugged it in and the original PSU showed that it was missing -5V. Well to test the boardset, I plugged in a PC power supply and it actually fired up and worked!

The next time I turned it on again with the PC power supply it gets stuck resetting itself and it's been that way since then. Game boots up, "UNIT OK", then it goes into the audit menu and automatically pages through all the options on it's own. After that it constantly blue-screens and resets forever.

I finally rebuilt the original PSU today and it works great, but I'm still getting the reset issue.

BTW, it has original rams on it, not the upgraded rams.
 
Try unplugging the I/O board (while the power if off, of course). Sometimes they will go bad and act like the controls are pbeing pressed. This can leave the CMOS is an unstable condition. You should also pull the batteries and leave them out for 5 minutes to force it to reset the CMOS.

Also, Don't forget to measure the voltages just to make sure they are still right. Switchers can drift and mess up the voltages. Don't just test the +5V.

ken
 
Just got a defender the other day. It was in really good shape, very clean. Plugged it in and the original PSU showed that it was missing -5V. Well to test the boardset, I plugged in a PC power supply and it actually fired up and worked!

The next time I turned it on again with the PC power supply it gets stuck resetting itself and it's been that way since then. Game boots up, "UNIT OK", then it goes into the audit menu and automatically pages through all the options on it's own. After that it constantly blue-screens and resets forever.

I finally rebuilt the original PSU today and it works great, but I'm still getting the reset issue.

BTW, it has original rams on it, not the upgraded rams.


Potential [voltage] reading on 4 corners of a couple of RAM chips please...

Saltbreez
 
Did you replace the 18K 25v cap on the ps?

Yea, I ordered Bob's deluxe repair kit. Basically, everything got replaced except the two power transistors and the pin-headers. I'm reading 5.1v with no load and also nominal -5 and 12v as well.
 
Yea, I ordered Bob's deluxe repair kit. Basically, everything got replaced except the two power transistors and the pin-headers. I'm reading 5.1v with no load and also nominal -5 and 12v as well.

Then it is not a ps problem. Test voltage on the 4 corners of the RAM as asked for by Saltbreez. Pick one, it doesn't matter which one there are 24 to choose from.
 
The bad news is: this is not likely a power supply issue.

Before I went any deeper with one of these old boards that was acting up, I would replace all 24 RAM, both decoder chips and the 6809.

Saltbreez

I would do the touch test on the CMOS RAM, to see if it is getting hot, and failing. Thoughts?
 
*bump*

Okay I replaced the CPU, decoder chips and did the 4164 ram upgrade. No effect. Any ideas?


Yep, it is time to pull out the trouble shooting guides and walk through step by step. If the login probe section does not solve this [and based on description it may not] then you will need to complete the Williams CPU oscilloscope troubleshooting section.

FYI, I have a working MPU for trade + $$

Saltbreez
 
Does it still fly through the setup screens on its own even with the I/O board unplugged? Can you get to the diags and test the cmos and roms?
 
try a different ROM board and clean the 40 pin header on the CPU board with 250 grid sand paper.
 
One other thing I forgot to mention, the game no longer makes that really annoying startup sound whenever it is turned on. It used to make the sound when it worked properly the first time. It couldn't be the sound board causing the issue, could it? Will the game run without the sound board?
 
It will run without the sound board. You cna test the functinality of th esound board by pressing the push button on the sound board while it is powered up. This will cause the card to cycle through the demo sounds. You will need to power it down to shut it up.

If it is completing the POST (Power On Self Test) and then resetting, there is poebably something wrong with either the ROMs or the main board. It is very difficult to diagnose via message board. If there is another collector nearby that can bring a known working boardset over, you can easily determine what the issue is by swapping boards in and out in an orderly fashion.

ken
 
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