Wednesday, 9 May 2012

Asteroids PCB findings


 okay, my gameroom took some time so the Asteroids Restauration had some days off.

Finally I`ve now again some time to spent  investigating the PCB. Last known state was, that PCB isn't working with black screen and no sound.

Step 0
So I built a PCB connector giving 30VAC, 5V and GND to the PCB. For the first tests I only need 5V and GND:

Step 1
 With this setup I measured the MCU Pin40. My Logic Probe is blinking here, means the PCB makes a continuous reset.

Step 2
So I checked the ROMs. A rom compare shows that all roms are OK (vers.1)

Step 3
Cut the vector state machine generation from the CPU. To I cut Pin1 from IC L6. The reset line is now high.

Result : The PCB has an error in the vector generation circuit. Means also, that the CPU is working and that the circuit for watchdog / reset generation is working. Thanks to Speleo for helping me with these findings.

Since the vector state generation circuit is a very ttricky one I give the PCB to speleo. Hope he can help me.

Next the vector video output :) Cebulba gave me a working Asteroids PCB. This way I can continue testing the deflection board and power circuits finally.

Check the deflection board

Step 0 : Eye Check :
The silver color Elko right hand side is damaged and was ripped somehow. Afterwards it was glued. So perhaps this one must be replaced.
The poti for brightness control is totally screwed up. Replace it.
The poti for contrast is not destroyed, but is rusty. Replace it.
All connector solder points must be resoldered. The solder is very old.

Step 1 : Measured the transistors: No short between E and C. Putting the multimeter to diode setup and measured the diode voltage between base (B) and emittor (E). It should between 0.4V and 0.7V. Done this for all transistors. Take a look at the numbering of the parts. The first number denotes the circuit for generate x and y (and z?). Measure the diodes, too.

Here was everything okay.

Step 2 : Measure ESR of Elkos. All Elkos ok,  (low esr value).

I decided not to connect the deflection board, coz I`m waiting for the Poti. Without the poti further in system testing makes no sense.

Check of power system

Step 0 : Put the known working PCB in the CAB and turned it on. No sound.Add some coins and pressed player 1 start. Coin buttons showed some behaviour. So again the question why sound is missing?

Step 1 : Checked wiring of speaker. On wire was not connected. Connected it.

Result : PCB plays blind. :)

Did some further measuring of voltage on PCB x and y ouput -> jumps between 1-4V-7V somehow.

In summary this was a big step. A working PCB plays blind and I have some idea to make further progress on the deflection board. Game PCB must be repaired either the way.

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