Amiga 600 schematics nearly put into Kicad

[Acill]

Originally Posted by Mick

I'll have to see what Acill finds and maybe buy the board off him if it's a write off, spend a while checking everything. As if designing it wasn't hard enough you have to also navigate a minefield of dodgy PCB manufacturers.

I am at the end of what I think I can do with the one I tried to get working. Ive started up my day job again today and am short on time I can spend fault finding on a partial built board. I can also send on parts I have as spares. I think the donor board was a bit far gone and a bad idea to use, but the other one is fine. I am happy to send it on to anyone wanting to give it a go.

This was given to me, so no charge to who it goes to next. Maybe just shipping if overseas.

[Acill]

As if designing it wasn't hard enough you have to also navigate a minefield of dodgy PCB manufacturers.

I can also have some made through the place I use here in the US once we find the mistakes and get them taken care of. I would also say I can have a friend of mine look at the schematics and board design files, but his company uses Pads and would not do it for free. He isnt cheap, but his board house is good and I get a deal since we use them at work for prototyping.

[Mick]

Ok thanks Steve, do you mean yours should be correct or do you think I need to change the way Commodore did it for the 2075?

I have just realised something else that might be causing a problem with video output, the 2.61K resistor for the YTRAP needs to be a 1% resistor so it needs to be accurate, but if you look at the schematics I don't have it connected directly to VCC but VID which goes through the 4.7Ohm 5% resistor (R406) first. Does this mean the internal circuity isn't being enabled or will it be okay because it's still within 1% of 2.62K?

[Mick]

Originally Posted by Acill

I am at the end of what I think I can do with the one I tried to get working. Ive started up my day job again today and am short on time I can spend fault finding on a partial built board. I can also send on parts I have as spares. I think the donor board was a bit far gone and a bad idea to use, but the other one is fine. I am happy to send it on to anyone wanting to give it a go.

This was given to me, so no charge to who it goes to next. Maybe just shipping if overseas.

Hi Acill no problem, can you go into a bit more detail about what is happening (or rather not happening) with it and what you have tried. Did you test any of the chips on the donor board? If you can send the board I can hopefully find someone else with the time to try to diagnose what is wrong. I appreciate you helping anyway I'm sorry it turned out to be a bit unfinished. It seems like a bit of a waste of money getting any new boards done with the minor fixes until I know what was wrong with this one to stop it from working at all.

[Stedy]

Originally Posted by Mick

Ok thanks Steve, do you mean yours should be correct or do you think I need to change the way Commodore did it for the 2075?

I have just realised something else that might be causing a problem with video output, the 2.61K resistor for the YTRAP needs to be a 1% resistor so it needs to be accurate, but if you look at the schematics I don't have it connected directly to VCC but VID which goes through the 4.7Ohm 5% resistor (R406) first. Does this mean the internal circuity isn't being enabled or will it be okay because it's still within 1% of 2.62K?

The YTRAP should only affect the colour on the composite video and the chrominance output of the Y/C (S-video) signal. If the video syncs are present and correct and pixel data is arriving from Denise, you should get some video signal.

I'm still working through schematics and layout, no issues yet though I will double check how the vagarious parts get fitted to route clock signals. Will collate the post-it notes and get back to you. A review like this takes 6-8 hours so I'm doing it over a few evenings.

@Acill

What would it cost to ship the prototype PCB to the UK?
I could take a look, would be toward the end of the month as I have two smaller projects to clear first.

I have Diagrom for A500/A600 for when I get around to fixing my dead A500 that might prove useful. Also have oscilloscope and logic analyser

[rvctech]

Video output (or lack thereof) is not really important in preliminary board bring-up. A DiagROM and serial output would probably be a good starting point to know if the board is "alive".

One would not even load the video output parts at this point.

[Mick]

I'll pay the postage to Stedy if Acill tells me how much and PM me his PayPal address.

Stedy, if you want I can send you latest files, I've added extra memory and clockport which was easy enough. The only thing that confused me was the _PWR_BAD signal where do I get it from? I've removed the PAL for now to try to keep things simple.




I am not even that bothered about an A600 motherboard unless new cases are made but it feels like some kind of crusade at this point, I've put so much into it I want to see it complete.

[Mick]

Ok so a theoretical situation, if you have 2MB onboard with the last 1MB using the same signals as the expansion connector what would happen if you also plugged in a 1MB expansion? would there be some sort of conflict?

[Jope]

Yep, it wouldn't be a stable configuration with two chips being selected for the same memory area.

[Mick]

I was just thinking because of things like the A314 project it probably would not be compatible in that case.

Do you think a CPU/fast ram accelerator could be made small enough to fit in the A600 expansion area if I turned the edge connector into a a500 style zorro? I'm kind of just messing around with ideas at this point until I can find out what is wrong with Acill's board.

Otherwise, what would be the best way to disable the second megabyte? jumper?

[Jope]

A RAS jumper similar to JP3 on the Rev6-8 A500 board perhaps?

[Mick]

I'll do that then.

Do you have any idea what R162 does? it connects to the expansion connector and is labelled _X1M.

[Mick]

There's a bit of a problem with that way I think, the A600 has its two memory chips split between RAS 0 and 1 instead of on the same row and so do the expansions so if I disable one row on the board I think when you plug in an expansion it'll have 3 chips active on one row and only 1 on the other. I'll need to disable one chip on each row. I guess I'll need two jumpers before the second chips on each row?

[Stedy]

Hi,

Still checking through the schematics, might have found something. Does the prototype A600 board have a working 6570 Keyboard microprocessor?

If that chip is missing or the 3MHz crystal does not start, the A600 will not generate the 500ms power on reset signal, via kb_reset. The MC68000 must be held in reset for 100ms to operate correctly.

Will draw out a few critical circuit to check them. Looking for the custom chip documents on my hard drive.

[Mick]

I've got no idea Stedy all I've really been told is it doesn't work.

If that's the case the keyboard controller is absolutely necessary then? there's not really much point in having the A500 keyboard connector in that case. Is the A1200 the same?

Once again thanks for the help.

[rvctech]

Originally Posted by Stedy

Hi,

Still checking through the schematics, might have found something. Does the prototype A600 board have a working 6570 Keyboard microprocessor?

If that chip is missing or the 3MHz crystal does not start, the A600 will not generate the 500ms power on reset signal, via kb_reset. The MC68000 must be held in reset for 100ms to operate correctly.

I'm not sure if that is correct.

From my reading of the schematic, _RST is generated by GAYLE, and this depends on the signal _KB_RESET which is an input to GAYLE. The _RST signal is the system-wide reset and also keeps the 6570 in reset.

The machine begins in a reset state (Q511 is ON) and _KB_RESET is de-asserted by the 555 (U14) output when it reaches its timeout (0.1uF capacitor charging via a 47K resistor to reach the threshold voltage).

GAYLE de-asserts its output _RST once its input _KB_RESET (driven by the 555 and output BJT Q511) is de-asserted.

This then brings the 6570, CPU and the rest of the machine out of reset.

The 6570 can generate a new reset at any time by re-triggering the 555. However the 6570 is not required to bring the machine out of reset and the machine should function correctly without it.

Of course if the 6570 is not loaded, then Q622 should not be loaded either, otherwise it will hold the machine in reset. R624 is also not meant to be loaded.

[Mick]

I spent a while comparing the schematics on Amigawiki to an original Commodore document and found quite a few discrepancies. Will any of these cause major problems?

E353R 47 not 68
E354R 47 not 68
E363R 47 not 68
E364R 47 not 68
C321 100nF not 3900pF
R321 360 not 1.5K
C331 100nF not 3900pF
R331 360 not 1.5K
R325 390 not 2K
R335 390 not 2K
C26 0.01uF not 0.047uF
C27 0.01uF not 0.047uF
C33 0.01uF not 0.047uF
C34 0.01uF not 0.047uF
C7 0.01uF not 0.047uF
C8 0.01uF not 0.047uF
C29 0.01uF not 0.047uF
C28A 0.01uF not 0.047uF
C28B 0.01uF not 0.047uF
C36 0.01uF not 0.047uF

These were mistakes by me I think:
E513R 68pF not 47pF
E514R 68pF not 47pF
E515R 68pF not 47pF
E516R 68pF not 47pF

I'm not sure about these:
On the internal floppy connector all 27 ohm resistors should be 68?

Are there any original Commodore schematics for rev. 2 so I can check the floppy section? or can anyone with an actual board handy check them please? the ones in question are E586R, E596R, E580R, E595R, E599R, E593R, E592R, E591R, E590R, E589R, E588R, E582R, E587R, E581R, E594R, E583R, E584R, E585R. I want to know if they're 27 or 68. I've looked at a photo of a 2B board and they don't have any markings. Actually they look a lot more like ferrite beads used elsewhere.

[nikoskob]

Hi Mick,
I have a rev 2B (or is it 2D A600 board?, i'll have to check).
I remember going through a few resistors on my board, and found that the resistors on my board were different to the values on PCB explorer.
I know that on my board, there are more 27 ohm resistors on the floppy than there are 68 ohm.
Just looking now, I notice that the R2 schematics from amigawiki look to be a better fit to my board, but I will double check when I get home. But I wont be home until Saturday afternoon (Australia time).
Hope you can hang out that long
If you want some close up photos of the board, let me know.
Cheers

[Mick]

I think 2B and 2D are a bit different but any info you can give will help me get a better understanding.

The Commodore schematics I looked at appeared to be for rev. 1 but those parts above differed to both Amigawiki rev. 1 and rev. 2 documents (the wiki documents matched one another but were different to Commodore). The floppy section for rev. 1 seems to be a lot different to rev. 2, the signals are all connected to the internal floppy connector directly on rev. 1? it'd be nice to see original rev. 2 schematics but doesn't look like they're anywhere.

The 2B board I was looking at was this:
https://www.bigbookofamigahardware.c...0mbrev2b_1.jpg

There's no markings at all on those.

[nikoskob]

Yep, see what you mean, I only have the rev 1 schematics too. Rev 2 seems elusive, apart form the amigawiki one.

When I get home this weekend, I'll take some close up pics of the rev 2 board I have, but mine definitely has resistors on the floppy section, not ferrite beads like the BBOAH pic.

Once I get the pics, i'll try and post here.

If you need pics of the bottom, let me know.