Recent content by dave_m

Hello and welcome, You may be able to perform an in-circuit checksum of the ROMs using daver2's fantastic diagnostic called PettestE2KV04. Look for the binary here: pettest4. Burn the 2K byte binary into either a 2716 EPROM, 2816 EEPROM, or in the upper half of a 2732 EPROM. Carefully replace...

rglenn, Very good work so far. -dave_m

Wow, look at the Power Dissipation of the regulator with 'no heat sink'. The TO-220 package is the upper right graph , 2.5 Watts - terrible. The old TO-3 package looks a little better (upper left graph).

Good that you double checked the regulator output. Let’s hope you are lucky and it a bad 7812 instead of a failing component or intermittent low impedance issue on the video board that might be hard to find.

I agree, scope is set to AC instead of DC, but otherwise waveforms look good.

Random thoughts… The 6502 can test its own zero-page RAM that are in its two 6532’s. Maybe that’s the tests you are seeing? I don’t know how the 6502 knows about the zero-page RAM in the 6504 unless it gets status from the 6504 through the common RAM. But you show an error in the common RAM…...

The tabs did not work correctly for the memory map above. The first columns are for the 6502 which supports IEEE 488 communication and the last columns are for the 6504 which supports the floppy interface. I'll attach a link to the file here...

Ouch, you are right about the flash codes. Double check the part number of the 6530 in the 8050. I think it is different than the one in the 4040. The part number for the 4040 6530 (DOS 2) is 911466-04 while the one for the 8050 seems to vary with the drive mechanism . Here is a memory map I...

Vertical Drive - skinny pluse with a frequency of 60 Hz and a period of 16.6 mS at J7 pin 3 Horizontal Drive - wide pulse with a frequency of 15.6 KHz and a period of 64 uS at J7 pin 5 As daver2 says, disconnect P7 cable from PET main board first. Cable goes to monitor board.

Good work. I think zero page RAM for the 6502 processor is in its associated 6532 chip. That is a good sign that chip is working. Zero page for the 6504 and it’s ROM are in the 6530. Your logic analyzer seems not to be having a problem with the two CPUs sharing the data bus.

Witchy, In case you need the user manual for Commodore 5 1/4 dual drives. https://commodore.bombjack.org/commodore/commodore/CBM_Users_Manual_for_Dual_5.25_Floppy_Drives_Part_Number_(320899)_1980_Oct.pdf

OK, good, you did check that all the RAM chips in the system are 300 nS or faster. On the 4040, the center light and drive lights flash twice on power on. After that, the center LED will indicate only errors after Read/Write operations. It is not a power indicator. You can clear the error with...

Witchy, Hang in there. This 4040 is much harder to fix than a PET. The /Write Enable to the RAM is gated with a 2 MHz clock so it will only be a negative going 250 nS pulse. Switching out the 6532 may be a red herring as the red light may only indicate an error. The drive indicator lights should...

As you may know the two CPUs are running on opposite phases of the 1 MHz clock and sharing the RAM. This means two RAM accesses within 1 uS. The faster the 2114 RAM the better. I would not use the older 450 nS access RAM that the PET boards can use. Try to use 300 nS or faster if possible.

Jim, So good to see your message. I have many of your gadgets for the Commodore computers. They are all so useful. -dave_m