exxos's Atari, Amiga & retro forum

stephen_usher wrote: 14 Apr 2025 09:15 Sod's law states that it will be the last component left to replace after you've done all the others, chasing red herrings. :-)

I feel your assessment is correct.

I just did a very quick check and the onboard ram seems to have no CAS. It appears to be present at U35 pin 12 and on the external trapdoor RAM, but not on the internal RAM. The only thing there is RP203. Or a bad trace?

CAS for the trapdoor takes a different route entirely.

Smoking gun perhaps?

OK, ignore me for now, I had the wrong RAM pinout...


:dizzy:


3/10 must try harder...

OK, so despite some initial confusion, RP203 is fine.

I was confused because the arrays are not commoned, so it is essentially 5 resistors in a pack, and 2 pins showing per resistor. So 1 & 2 is a resistor, as is 3 & 4 etc.

Knowing that I was able to verify each resistor was fine. I was initially trying to test like it was commoned to pin 1.

Pretty much all that's left is the RAM, and fortunately I have spares.

And it isn't the RAM either.

I have a hint from another site that suggests bad address lines from U34, so I will check all the connections are as expected.

rubber_jonnie wrote: 14 Apr 2025 14:18 And it isn't the RAM either.

No luck...

HigashiJun wrote: 15 Apr 2025 03:37

rubber_jonnie wrote: 14 Apr 2025 14:18 And it isn't the RAM either.

No luck...

No. I tried to get DiagRom running but that doesn't work though I haven't yet tried to put a serial cable on it to see if there is output there, but on screen is corrupted.

I need to get back to the schematics, it's a bit of a head scratcher

Hmm.

So I have popped in DiagRom and I get zero output on the serial port...

I hooked up my terminal to an ST with diag cart and that worked fine, so I see no reason why it wouldn't.


Oddly, since I replaced the RAM, one is now working, as in it heats up whilst the other 3 stay cool.

I take it that you've 'scoped the bus (at the RAM end) and checked the power and gnd pins on the chips? Assume nothing. :-)

stephen_usher wrote: 15 Apr 2025 10:55 I take it that you've 'scoped the bus (at the RAM end) and checked the power and gnd pins on the chips? Assume nothing. :-)

I did and all power was good, however I'm just going to buzz out things again and scope again. I have already buzzed out U34 to RP201 and RP202 and they are fine, so I will do U35 to RP203 next.

The _OE connections on both are fine, so I also need to check the inputs to both and from U34 back to Agnus for the address and U35 back to Agnus for the _CAS/_RAS and _WE lines.

Then I need to double check the lines across the RAM. I can't help but think I have a broken trace or via somewhere.

OK, so I have U35 to RP203 and it's all good. I've also buzzed out U35 to Agnus and they are all good.

Next I need to buzz out U34 to Agnus.