Another Defender rug problem.

landsteam

Member
Joined
Sep 30, 2010
Messages
59
Reaction score
17
Location
HUNTINGTON, New York
My Defender was working fine for years. Now boots up to the rug pattern. I have 3 led's on the power supply. I reset the ram and rom chips, I also rest the connector between the boards. How do I check to make sure I am getting the correct voltages?
 
My Defender was working fine for years. Now boots up to the rug pattern. I have 3 led's on the power supply. I reset the ram and rom chips, I also rest the connector between the boards. How do I check to make sure I am getting the correct voltages?

Does it halt at the rug pattern or reboot after ?

LEDs show voltage present not correct voltage. get yourself a cheap digital multimeter, a copy of the schematics and measure the voltages at the test points on the PCBs to start with.

on the schematics "Defender_Drawing_Set_(16P-3001-101_R-T)_April_1981.pdf" pages 10 and 11 that show the pcb layout and the schematic. Measuring the voltage between Ground and Test point 1 (TP1) should read 5.1v or close to it (not over 5.25, not under 4.75v) the close to 5.1 the better.

then need to check the -5v rail (they can go bad). Measuring the voltage between Ground and Test point 5 (TP5) should read -4.9v or close to it (not over -5.25, not under -4.75v) the close to -4.9 the better.

similarly, need to test the 12v rail - test point 4 should read 12.1v or close to it.

check those then report back.

you can also check the voltages at the corners of the RAM ics . page 4 of the schematics shows the main cpu layout. ICs 1R thru 3Z ar ethe ram ICs. the black dot in the upper left corner of each ic indicates pin 1.
Ground is the top RH corner of each ic, so measure between ground (pin 16) and pin 1 (-5v), pin 8 (12v) and pin 9 (5v)

check the voltage on a few ram chips or all ram chips and report those back.
 
The rug pattern keeps on repeating.
I did a search and can't find the drawing set to locate the test points on the CPU. All the led's on the rom board go on for a second at power up then they all turn off. Can someone send me that info so I could check?
Could I ground the meter to a screw holding the PCB and use the red probe to test the voltages at the ram chips?
 
The rug pattern keeps on repeating.
I did a search and can't find the drawing set to locate the test points on the CPU. All the led's on the rom board go on for a second at power up then they all turn off. Can someone send me that info so I could check?
Could I ground the meter to a screw holding the PCB and use the red probe to test the voltages at the ram chips?

http://www.robotron-2084.co.uk/manualsdefender.html

and yes i commonly check that way using crocodile clip leads. importantly you need to know if the wiring and/or header pins are causing a drop in voltage from the power supply output to the rams (ie is the 5v rail lower at the ram compared to the power supply test point ?) as an indicator of soem work needed to reflow solder and clean/replace pins or header sockets etc.
 
grab all of the manuals for defender while you are at it - in the "later series setup booklet" coded "16p-3001-103 R-T" july 1981.

starting on page three there is a section on rom/ram tests and interpreting the three led lights on the rom board that will (or may) help diagnose some issues such as faulty ram etc.

identify what code is being flashed up and post here.

some ideas posted here:
http://forums.arcade-museum.com/showthread.php?t=41578&highlight=defender+reboots
 
Last edited:
All 4 led's flash for a second, then nothing.
I also printed those manuals but I still can't find the test points on the CPU board.
Could I be helped out with that?
I hate looking at a dead machine.
 
All 4 led's flash for a second, then nothing.
I also printed those manuals but I still can't find the test points on the CPU board.
Could I be helped out with that?
I hate looking at a dead machine.

There isn't much in the way of test points on the cpu board, check the voltages at the corners of the ram chips. The repeating rug pattern can be due to problems on the cpu board, but is more likely a voltage or rom board problem. Reseating the rom chips may help. Once you've checked your voltages, see if the rom board chart here gives you any clues:
http://www.arcadesolution.com/rom.html
Sometimes the ribbon cable on the rom board loosens up, you can try wiggling or reseating it.
 
All 4 led's flash for a second, then nothing.
I also printed those manuals but I still can't find the test points on the CPU board.
Could I be helped out with that?
I hate looking at a dead machine.

the test points i referred to are on the power supply PCB. they are little metal posts with a round top, about 1/4" high at most
 
Back
Top Bottom