Icky - Progress

[exxos]

What are your thoughts on the next board around this area?

My initial thoughts are the DMA you had in before has some fault.. Probably best leave the current working one in place and wait for the new 1772 to come...

If you can try both chips in a STFM then it will help test if they are faulty or not.. I guess it could be possible that without the STE buffer circuit, the DMA vs 1772 data bus conflict could possibly damage one or both of the chips.. Will be useful if you could test both chips on the working machine to verify they are not damaged..

Currently I still suspect we need the STE buffer circuit in place... But this isn't going to be so easy to set up on the remake board..

Probably the way to go would be to run HDCS via a flip-flop to delay by 1x 8Mhz cycles... I think this would pretty much do the same job as what the STE circuit does... As if HDCS is delayed, then the hard drive would not output data until later there would not be any need to isolate the databus ... At at least in theory the hard drive should not be hogging the databus when it is not selected... But I think we proved this as you type the line yesterday the floppy drive was working at that point.. So I think there is definitely a bus conflict going on..

But again, lifting the 1772 databus out of the circuit should mean the hard drive should work but not floppy drive of course...As now the hard drive is working, after changing the DMA, I can only assume that chip is damaged for whatever reason, so definitely worthwhile trying this on a working machine..

If either of the DMA or 1772 turns out to be faulty (ones you have been currently using) it is likely data conflict which is damaging them.. In which case we will pretty much know at that point what the issue is and how to solve it..

If neither of the chips are faulty, the we still have some figuring out to do

[Icky]

What are your thoughts on the next board around this area?

My initial thoughts are the DMA you had in before has some fault.. Probably best leave the current working one in place and wait for the new 1772 to come...

If you can try both chips in a STFM then it will help test if they are faulty or not.. I guess it could be possible that without the STE buffer circuit, the DMA vs 1772 data bus conflict could possibly damage one or both of the chips.. Will be useful if you could test both chips on the working machine to verify they are not damaged..

I am wondering if the find by PaulJ

Ok, I've had a hard time getting the floppy tests working from the diag cart.. Also the serial has been intermittent that is sometimes it starts and sometimes not. Well I found the issue!! . Pin 7 of the MAX238 is routed to pin 3 (RD) of the serial connector which is additionally routed to pin 19 (RD) of the 1772. The 1772 didn't like the negative voltage applied to its RD pin. Cut the run from serial pin3 to 1772 pin 19. It has to be cut to the right side of the via where pin 19 of the 1772 goes to pin 1 of the external floppy connector. Its late here so I'll post a pic tomorrow.

may of damaged the WD1772 as was running in that state for a long time.

Currently I still suspect we need the STE buffer circuit in place... But this isn't going to be so easy to set up on the remake board..

Probably the way to go would be to run HDCS via a flip-flop to delay by 1x 8Mhz cycles... I think this would pretty much do the same job as what the STE circuit does... As if HDCS is delayed, then the hard drive would not output data until later there would not be any need to isolate the databus ... At at least in theory the hard drive should not be hogging the databus when it is not selected... But I think we proved this as you type the line yesterday the floppy drive was working at that point.. So I think there is definitely a bus conflict going on..

I was looking to see if we could come up with some sort of breakout pcb board that plugs into the BAD DMA / WD1772 sockets that does the STE circuitry and has the BAD DMA and WD1772 plugged into it.

But again, lifting the 1772 databus out of the circuit should mean the hard drive should work but not floppy drive of course...As now the hard drive is working, after changing the DMA, I can only assume that chip is damaged for whatever reason, so definitely worthwhile trying this on a working machine..

If either of the DMA or 1772 turns out to be faulty (ones you have been currently using) it is likely data conflict which is damaging them.. In which case we will pretty much know at that point what the issue is and how to solve it..

If neither of the chips are faulty, the we still have some figuring out to do

Hmm this might be difficult to fully test. I have the STM 520 where I can place in the NASTY DMA as I am calling it (the one I have been using in the STF Remake) as this where I got the NOT SO BAD DMA (the one that is currently working in the STF Remake) from.

However the WD1772 is soldered and i am not messing with that board.

Next steps will wait for WD1772 to try in STF Remake and try out NASTY DMA in STM 520.

[PhilC]

You guys have been working hard with this.

I do have an internal satandisk, is there any way I can interface that externally to help with the testing?

[exxos]

I am wondering if the find by PaulJ
may of damaged the WD1772 as was running in that state for a long time.

Possibly yes. Wasn't the hard drive working initially right at the start ? Can't remember...

I was looking to see if we could come up with some sort of breakout pcb board that plugs into the BAD DMA / WD1772 sockets that does the STE circuitry and has the BAD DMA and WD1772 plugged into it.

Possible, but that's going to be another huge waiting time for that PCB... I was trying to think of proving the issue some easier way meanwhile... What I don't like is its another 3 logic chips to mash onto the thing.. I want to see if there are simpler ways of doing the fix with 1 chip anyway.

Next steps will wait for WD1772 to try in STF Remake and try out NASTY DMA in STM 520.

Hopefully 1772 will arrive tomorrow...

BAD DMA has been upgraded to NASTY DMA now then Make life easier if it fails to work on another machine...

[PhilC]

If you can come up with a schematic, I can make it on a breadboard?

[exxos]

If you can come up with a schematic, I can make it on a breadboard?

I was just trying the flip-flop simulator see what the delay was....

d1.jpg (83.42 KiB) Viewed 3246 times

For some reason it ends up being 36ns..

I think an easy solution will be to get a simple buffer like a 74LS07... Link all the buffers in series... Then lift the DMA pin 24 (HDCS) to the input of the buffer chip, then the chained output of the buffer goes to the now free DMA pin 24 in the socket..

Basically each buffer would add about 10 ns delay, so 6 buffers would be 60ns...

Have you tried a hard drive then or not ?, I have lost track...

[PhilC]

No I don't have a negative but do have an ultrasatan, altho it's an internal one

[PaulJ]

Icky, if you didn't use serial it most likely had no effect other that possibly causing errors on the serial 6850. If you had serial connected the -12 volts was routed to the read pin of the 1772. The 1772 tries to clamp the pin from going negative. On the scope you would observe a sawtooth waveform that ran from -1 volts to -2 volts. I put quit a bit of time on mine in this condition an the 1772 and serial work reliably. I have not hooked up anything to the dam port yet, hopefully today.

[exxos]

dam port That can be the new official name for it

[Icky]

Icky, if you didn't use serial it most likely had no effect other that possibly causing errors on the serial 6850. If you had serial connected the -12 volts was routed to the read pin of the 1772. The 1772 tries to clamp the pin from going negative. On the scope you would observe a sawtooth waveform that ran from -1 volts to -2 volts. I put quit a bit of time on mine in this condition an the 1772 and serial work reliably. I have not hooked up anything to the dam port yet, hopefully today.

I had used the serial lines for some time whilst trying to get the video sorted. Am not surprised if the chip was damaged anyway as it came out of a donner ST.