Tempest PCB stuck paused

putyoursoxon

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Working on a tempest board, all voltage on AR and board measure good with exception of X Y out AC are 0v. I have not plugged the monitor in. Game not playing blind. Will not enter test mode. Volcano LEDs are stuck on, but probing pin 40 of the 6502A it is not resetting. Hitting the reset button will toggle pin 40. I confirmed the dips that it's not in freeze mode. Plan on rebuilding the AR even though voltages are good. What should I be checking on the board itself?
 
If it's not playing blind, it just sounds like the CPU isn't running. Which means there could be any number of things wrong. Bad CPU, missing clock, bad RAM, bad ROM(s), bus issues, decoder logic issues, etc.

Not something a rebuild of the AR is going to fix. You just need proper board-level debug tools, or send it to someone who repairs these.

And for the AR, don't replace the caps, or shotgun a bunch of parts with a kit. If the AR is working, all you need to do is replace the 2N3055 bottlecap transistor with a legitimate replacement from a trusted source. (APAR, Digikey, or Mouser). Not Arcadeshop, ebay, Aliexpress, Amazon, or anyone else where you can't trace the part to the manufacturer. There are many fake parts out there, and it's the one place where you absolutely want a legitimate part, because a fake transistor can damage your game board.
 
If it's not playing blind, it just sounds like the CPU isn't running. Which means there could be any number of things wrong. Bad CPU, missing clock, bad RAM, bad ROM(s), bus issues, decoder logic issues, etc.

Not something a rebuild of the AR is going to fix. You just need proper board-level debug tools, or send it to someone who repairs these.

And for the AR, don't replace the caps, or shotgun a bunch of parts with a kit. If the AR is working, all you need to do is replace the 2N3055 bottlecap transistor with a legitimate replacement from a trusted source. (APAR, Digikey, or Mouser). Not Arcadeshop, ebay, Aliexpress, Amazon, or anyone else where you can't trace the part to the manufacturer. There are many fake parts out there, and it's the one place where you absolutely want a legitimate part, because a fake transistor can damage your game board.
If the ram or roms were bad wouldnt the board be watchdogging?
 
RAM failures should be indicated by tones.
ROM failures should be indicated by letters on the screen.

Check TM page 16 for selftest procedure.
 
RAM failures should be indicated by tones.
ROM failures should be indicated by letters on the screen.

Check TM page 16 for selftest procedure.
Doesn't enter self test. Does nothing. 6502 isn't watchdogging hitting the reset button on the PCB will toggle pin 40 on the 6502. I thought maybe it was in freeze mode but verified the dip settings.
 
Doesn't enter self test. Does nothing. 6502 isn't watchdogging hitting the reset button on the PCB will toggle pin 40 on the 6502. I thought maybe it was in freeze mode but verified the dip settings.


Start my checking to make sure you have all of the clocks. CPU won't do anything if there is no clock.

This isn't a freeze mode issue. This sounds like the CPU just isn't running. Is there any activity on the busses? You need more info than just what the reset line is doing.

If all clocks are there, next thing I'd do is check the CPU in another board, to make sure it's good.
 
Start my checking to make sure you have all of the clocks. CPU won't do anything if there is no clock.

This isn't a freeze mode issue. This sounds like the CPU just isn't running. Is there any activity on the busses? You need more info than just what the reset line is doing.

If all clocks are there, next thing I'd do is check the CPU in another board, to make sure it's good.
Clocks are there, there are activity on the buses. Swapped another 6502A in with same result. I will start pulling the roms and verifying. If they check good I guess I will start pulling ram and testing it
 
Power the board up with the test mode switch ALREADY flipped on, before you apply power.

This will force self-test to run, which isn't the case when you flip into test mode after power is on.

Listen for RAM error beep codes. You will know if self-test completes if you can press buttons on the CP and hear a beep for each button.

If that's the case, check to see if the XOUT/YOUT AC voltages are not zero, and are doing something.
 
Have tried entering test and starting in test. Neither will do anything. Looking over the board it hasn't been reworked before. The 2114s are the only thing showing corrosion on the legs.
 
What level is the reset line (pin 40) normally at, and what happens when you push and hold reset?

(You said pressing the button toggled it, but that doesn't indicate what level it was toggling from.)

What is the voltage on the non-grounded side of C85?
 
What level is the reset line (pin 40) normally at, and what happens when you push and hold reset?

(You said pressing the button toggled it, but that doesn't indicate what level it was toggling from.)

What is the voltage on the non-grounded side of C85?
High - Press reset - Low - Release - High

15.14VDC
 
You just need to start digging at this point then. The best thing to do would be to have an FPGA Catbox, in which case you'd plug it into the CPU socket, and see if it can access all ROMs and RAM. In lieu of that, you can pull and test all ROMs. You should also clean the inner and outer faces of all socketed chips with a Dremel wire wheel brush, then apply some DeOxit to them when you reseat them, after you check them in a burner.

There's only going to be so much you can do at this point, without the right tools. Your best bet is to send it out. Or get a logic probe and start tracing logic and see if you can get lucky.

Also, the importance of visual inspection cannot be overstated. Hold the board up to a light, and look for shorts with light shining THROUGH the board. This helps things stick out that you may not see otherwise.

Pulling all of the RAM one by one to test them is not advised. You're more likely to cause new problems doing so.
 
Pulled all the ROMs. Replaced everything that was bad. New ones verify good. Now I get a beeping but that's about it. At first I thought it was the RAM test, but beeps whenever in test or not. Also the speed of the beeps change, never stops as long as its on, hitting reset will give you a momentary pause before it starts again. No change on the X Y out
 
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