Recent content by daver2

Basically, the AC supply arrives at the monitor PCB from the transformer. Diodes CR19-CR22 are a full-wave bridge rectifier to convert the AC voltage into a DC voltage. Capacitor C1 smooths the pulsed DC from the bridge rectifier and feeds the input to the 12V voltage regulator (VR1). The 12V...

The only "PET power supply" that is actually connected to the monitor PCB itself is an AC supply directly from the transformer - so no active or passive components at all... The rectification, smoothing and voltage regulation is all done on the monitor PCB. Yes, you can feed an external AC or DC...

Now you have it out on the bench, you can measure the resistance with a multimeter. There should be approximately 1 MOhm between the two outer pins. As you turn the potentiometer, the resistance from the centre pin to one of the outside pins should increase, while the resistance from the...

Yes, this is mentioned in the thread (post #4). Mike, the cursor is actually in the correct place for the initial 6809 boot screen... 14th line down. You are not too far away. As Andy and I have previously stated - do you have the correct character generator ROM installed? Your post #5 states...

Mike, So, is what you are now saying, with a 6809E in the CPU socket (with or without SuperPET ROM?) - that the 8032 works correctly in 6502 mode but you do see something (albeit incorrect) on the screen when in 6809 mode? Dave

It had to be the E that was in it then. The 'bare' 6809 would not (or should not) have worked. Dave

I wouldn't worry about undershoots like that too much at this point in time! Dave

It sounds more like something is loose to me... Either a potentiometer (as you have already found) or a loose wire in a connector or a connector pin that has a cracked solder joint. When you say "videoboard" what are you meaning? The logic board within the lower half of the metal case or the...

Since the OP was last seen when they posted the message - I would probably say there are no further updates (nor will there be either). Dave

My initial gut feeling is 'no' - as the real-mode CPU does not have a transparent memory management unit (as such). I did once use a 486 CPU to directly address 4MB of EXTENDED RAM from real mode DOS... But I was pulling a few tricks... Dave

>>> I seated the 2732 according to the little picture on the PCB (essentially at the bottom). That is correct! You can 'binary copy' the source image file four times to make a bigger file, then burn that into the 2732. COPY /B infile+infile+infile+infile outfile Where <infile> is the 1K file...

The 6809 and 6809E are not compatible with each other! Please, please, check the data sheets and data books BEFORE exchanging a part with something else. In particular, ask us on VCFED first BEFORE doing the exchange. For most parts, a suffix letter may be inconsequential. However it may also...

The value of the decoupling capacitors are fairly irrelevant. As long as something is fitted - you are good to go. I am not convinced a 2732 will work in here. A11 (on a 2732) is the same pin as /CE (on a 27128) and this could cause problems. The ROM image is 1K ($000 to $3FF), a 2732 is 4K...

If the /IRQ pin goes permanently low, it probably indicates that the associated CPU has given up executing instructions... That is one possibility. There are other scenarios of course... Can you post a link to the schematic for the adapter you have used, and for the EPROM image? Dave

It is programmed by the BIOS via registers. It is not a ROM, EPROM or anything like that. The 8259 was originally identified as a programmable interval timer (PIT) whereas it is a programmable interrupt controller (PIC). A different device. Dave