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jbilander / SF500

Spitfire 500, A low-end 14 MHz Accelerator with IDE and 4/8 MB fast RAM for the Amiga 500.
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14Mhz perfect.. but not at 7Mhz :( #7

Open bekafoin opened 1 year ago

bekafoin commented 1 year ago

Hi, I don't know if this is the right place to ask this but I have a "little" problem. I made this card following the instructions provided. When finished, I tried it in my A500+. The card works perfectly at 14Mhz (8M fast ram+ ide) but as soon as I switch to 7Mhz, the AMIGA crashes. Also the Amiga does not start when the switch is in the 7Mhz position (green screen). I tested the clock frequencies C7M, C14M, I have 7Mhz and 14Mhz. I also tested the CLKCPU signal, it goes well from 7 to 14 with the switch. I don't know where the problem can come from. Maybe you can help me? ps: I'm making a new board to see if I have the same defect but I'm still missing some components.

jbilander commented 1 year ago

Hi, since it seems to be a problem with the 7 MHz, are you using a PLL-chip (NB3N502) that also has the reference clock signal output (REF)? Otherwise it won't work with 7 MHz. If yes, can you try the Accelerator in another machine to rule out if it's your Amiga or the Accelerator that is the problem. Green screen normally means you have problem with the chip ram in the Amiga. Run the AmigaTestKit to test all ram. I haven't heard any problem like you describe with SF500 before. Are you using components from reputable dealers like Mouser or Digikey? Buying ICs from AliExpress sometimes you get bad components mixed with good components.

bekafoin commented 1 year ago

Hi and thank you for your reply. I measured 7Mhz on the REF pin. I also have 14Mhz on the CLKOUT pin. The NB3N502 seems to be working fine. The frequency also goes from 7 to 14 or from 14 to 7 when I use the switch on the CLKCPU pin. I have another A500+ but haven't tested it on this machine yet. I tested the ChipRam for about 30 min with the Amiga Test Kit without any faults. Where you're right is that my parts come from China :/ and I know it's a bit of a lottery... What's weird is that it works very well at 14Mhz. I'm going to do the test in my other A500+ and finish my 2nd board to see what happens. I'll come by to let you know. Thank you again for your work!!!

jbilander commented 1 year ago

Hi, ok it sound like your CLK:s signals are working ok coming from the PLL. Perhaps there is some problem with the IC (U11) in the RC-debounce circuit . The RC (resistor-capacitor) circuit uses the hysteresis in a dual-inverting Schmitt-trigger IC for proper debounce in hardware. If this IC is faulty then the switching won't work. Try and replace this part (or for testing remove it and put a fly-lead from VCC to the pad/line going to the CPLD will set it to start in 7 MHz). Check that you have the orientation correct of the IC. Also check that you used the correct values for resistors and capacitors in that circuit and that the soldering is ok.

One other thing is you could try is the older firmware that does not have the arbitration code implemented. It is more tested but you can't have anything connected to the expansion edge then (like a A590 or something) when you do the testing.

bekafoin commented 1 year ago

Hello ! I removed U11 and I connected the SW1 signal directly to VCC but the problem remains. I checked my welds and all the parts but it seems correct. Last thing, I used the old firmware (21 09 02) and this time I still get a green screen on 7Mhz and nothing on 14Mhz :/ . I put back the latest firmware which at least works at 14Mhz. I wonder if it's not my Chinese CPLD is the cause .... I'll see if I have better luck with the 2nd board!

jbilander commented 1 year ago

Hi, ok, yeah it sounds the CPLD could be bad. If you could try the Accelerator in another A500 and experience the same result then you could confirm the problem is with the Accelerator board and not that particular A500 machine you are testing on. Best of luck with the 2nd build. Let me know how it goes.

bekafoin commented 1 year ago

I tried the board in another A500+ with the same result, so the problem is with the board. I am waiting to receive what is needed for the 2nd board. I strongly suspect the CPLD! I'll be back to report... Thanks again for your help!

bekafoin commented 1 year ago

Hi! I received my 29F040B and I was able to finish my 2nd board. Everything works as expected! I continue to look for what is wrong with the 1st!