Help! A500 minimegachip chipram mod gone wrong!

[darksun9210]

Hi all.
I think I've done something wrong/bad....
So, I thought I'd fire up the ol' A500 and see what state she was in.
current spec.
Rev5 board, 3.1rom, ECS Denise, MiniMegachip, 512k+RTC trapdoor, IndivisionECS, Jens 68k socket clockport board. GVP A530 8meg ram, 4GB CF via usual curmudgeon of adapters.

so. fired her up without the GVP, trap door ram or clock port adapter attached. flashing power light, and eventually get a green screen (chipram fault). reset, guru meditation, click left mouse, rom screen. boot off floppy, get the workbench, 512k ram. ok fine. power off. plug in the trapdoor slot expansion. nope. no screen. power light, no floppy click. reset seems normal as in the caps lock light comes on and goes off... flick the switch to disable the trapdoor expansion, all ok again. shes a bit wobbly from cold, but she gurus out eventually, and then left click resets to the insert floppy screen.

now. for the minimegachip, the JP2 lower solderpad has been cut, but the upper pad has not been joined. the side trace from near the trapdoor slot has been cut, but a quick poke with a multimeter tells me its still live? accidentally touched the metal shielding and got a connection sound. not sure that's right?
the fly lead from the megachip board is connected to pin 36 of gary, and that's a good connection. also get a good connection from pin 48 on the 68k without moving the lead.

i've never got the minimegachip working right. even with a jumper on the upper patches of JP2. had 1.5meg chipram at best once, and I know fat agnus is working.

seems something nasty is going on with the trapdoor slot but I don't know where to start looking.

[darksun9210]

pics for a bit of clarity on what's going on

[Pat the Cat]

Hi all.
I think I've done something wrong/bad....
So, I thought I'd fire up the ol' A500 and see what state she was in.
current spec.
Rev5 board, 3.1rom, ECS Denise, MiniMegachip, 512k+RTC trapdoor, IndivisionECS, Jens 68k socket clockport board. GVP A530 8meg ram, 4GB CF via usual curmudgeon of adapters.

so. fired her up without the GVP, trap door ram or clock port adapter attached. flashing power light, and eventually get a green screen (chipram fault). reset, guru meditation, click left mouse, rom screen. boot off floppy, get the workbench, 512k ram. ok fine. power off. plug in the trapdoor slot expansion. nope. no screen. power light, no floppy click. reset seems normal as in the caps lock light comes on and goes off... flick the switch to disable the trapdoor expansion, all ok again. shes a bit wobbly from cold, but she gurus out eventually, and then left click resets to the insert floppy screen.

now. for the minimegachip, the JP2 lower solderpad has been cut, but the upper pad has not been joined. the side trace from near the trapdoor slot has been cut, but a quick poke with a multimeter tells me its still live? accidentally touched the metal shielding and got a connection sound. not sure that's right?
the fly lead from the megachip board is connected to pin 36 of gary, and that's a good connection. also get a good connection from pin 48 on the 68k without moving the lead.

i've never got the minimegachip working right. even with a jumper on the upper patches of JP2. had 1.5meg chipram at best once, and I know fat agnus is working.

seems something nasty is going on with the trapdoor slot but I don't know where to start looking.

OK. Rev 5 boards shipped with either 8371 or 8372 Agnus. You don't have an 8371 Agnus with more than 512K of chip RAM ever, IIRC.

Now, broadly, you have an issue with chip RAM. It seems to be with the memory board bringing the system down, but it could also be a problem with the mod to give Rev 5 A500s more than 512K of memory too.

A500 expansions come in all kinds of exotic variations, but they all do pretty much the same thing - add 16 bit memory. How that is configured depends partly on what Agnus revision you have fitted, as well as the card.

Post hires pics of the area around Agnus for any mods (bridges with solder between tracks cuts into tracks). Some of the expansion card to understand your issues with it would help.

If you can't photograph, examine and describe. It's probably a faulty component on the expansion board, or it could be something else too. Most all expansions have at least one strange behaviour.

It could also be the power supply is dying, or you have a local brown out for power. A530s can be greedy beasts. Disconnect it.

Examine the expansion and connector THROROUGHLY to see how well they connect, and if any bits of metal are touching where they should not.

[Pat the Cat]

Rev5 board, 3.1rom, ECS Denise, MiniMegachip, 512k+RTC trapdoor, IndivisionECS, Jens 68k socket clockport board...  4GB CF via usual curmudgeon of adapters.

That's a fair bit of hardware for many Amiga standard power supplies. Is there a floppy connected too? And how is the CF wired, to the SCSI bus, or to the floppy, or some other way?

[darksun9210]

right bear with me a bit, and i'll get you some photos.
i'm ruling the A530 from the start. she boots fine without the A530 or the trapdoor expansion, and boots fine with only the A530 - so i'll leave that out as not to confuse the matter. but just for interest, off of the A530's internal scsi bus, there is an Acard scsi2ide adapter, an IDE2CF, and a Kingston 133x 4Gb CF card in that.

also removed the clockport adapter card.

have connector blocked the floppy power line to add an additional externally routed male molex connector that would usually  plug into a female molex soldered to the back of the A530 PSU plug. its not pretty but its safe, and works.

the PSU does "sing" with a tiny bit of capacitor squeal, but it drives the A1200 I have loaded with a bliz040+scsi just fine (how long for remains to be seen

so. as we currently are.
rev5 A500 board
3.1 rom + fly lead
minimegachip with 8375 agnus + fly lead to pin 36 of gary
IndivisionECS with ECS Denise socketed
512k+RTC trapdoor expansion set to disabled. (was known good till "mod")
amigakit floppy drive
and NOTHING else.

[darksun9210]

trapdoor track "cut" but still seems connected when tested with buzzer function of voltmeter

https://1drv.ms/i/s!ArUfT_xm4N1vguUKScgGkivu8cDN8w

JP2 solder pad, bottom pad cut, but top pad not linked

https://1drv.ms/i/s!ArUfT_xm4N1vguULsd7cMzlSUAGOfQ

trapdoor expansion (set to disabled)

https://1drv.ms/i/s!ArUfT_xm4N1vguUNO51FZsLxh2CJtg

trapdoor tracks again, but with flash

https://1drv.ms/i/s!ArUfT_xm4N1vguUOueLyxgG1RjsJdw

JP2 Pad, CPU, KS3.1rom with fly lead

https://1drv.ms/i/s!ArUfT_xm4N1vguUPSQlBPGPEuN3QqQ

MiniMegaChip "Agnus". flylead solder pad looks a little lifted

https://1drv.ms/i/s!ArUfT_xm4N1vguUQnPE6uZ_zbynyBQ

Indivision + ECS Denise

https://1drv.ms/i/s!ArUfT_xm4N1vguUSC1U1JUo13yPnmA

Gary with flylead to minimegachip - connection fine, also tests fine to pin 48 on CPU

https://1drv.ms/i/s!ArUfT_xm4N1vguUTw14fXuBYqWbuyg

board overview

https://1drv.ms/i/s!ArUfT_xm4N1vguUUaiD1nCJFwEWYXA

proof that it all works

https://1drv.ms/i/s!ArUfT_xm4N1vguUWkkJtmuS-uVIIXw

[darksun9210]

ok, utter hackiness going on here.
in my annoyance at not being able to patch JP2 properly, I figured i'd trace what the solder pads connect to. took a bit of googling and poking with a sharp stick, but found that the bottom pad is pin 52 (address 23) of the 68k. the middle pad is pin 59 of agnus (Address 19). the top pad is pin 47 (address 19) of the 68k.
for reference, pin36 of gary/pin48 of 68k is Address20 that the megachip flylead clips to.

the agnus socket has rows of tiny holes all around the socket, stipped the ends of a piece of wire wrap with my teeth (don't do this at home kids), stuff one end in the hole next to pin 59 of agnus, success! connection from the other end of the wire wrap to the middle pad on jp2.

now wrapped the other end of the wire round pin47 of the 68k and fired her up.
no green chip ram error or flashy power light. booted straight up!

https://1drv.ms/i/s!ArUfT_xm4N1vguUXauc1EHAZH5aVvA

1.5meg chip ram! BOOM!

https://1drv.ms/i/s!ArUfT_xm4N1vguUYlXBp_1yCM8_bgQ

ok, so seeing as 1.5meg is the most I've ever had, and the trapdoor must have been faulty for longer than I understood.

[Pat the Cat]

Could just be the trapdoor RAM doesn't like working as chip RAM. A501s don't, the first version with 16 chips. Chips are too slow.

EDIT: BS, you just fixed it by bypassing the usual chip RAM mod. But it can be an issue with upgrading A500 chip RAM.

Great stuff!

[darksun9210]

quick update. turned the trapdoor expansion on to see if the magic is still happening.

its not.

blackscreen. on power on, the floppy sounds like it does a quarter spin but nothing else. power light is steady. no capslock flash code. no screen output at all. no floppy clicks, no nothing.

powered off, turned off the trapdoor ram module, turned back on, and all is well... either the ram expansion is faulty, or I've screwed up cutting the traces to the trapdoor slot I guess.

[Pat the Cat]

Could just be the wire to Agnus flapping about. Try shaking it when working properly.

Wire wrap mods like that usually go on the back of a board, to keep them out of harms way.

If it just won't start with the expansion, check the chip temps. It's probably gone short somewhere and gets hot really quick.

[darksun9210]

yeah, I remember the A501 wasn't the most... efficient...

the board I have is a four chip board with the chips rated at 80ns (I think?)
anyway, looks like i'm going to ami/fleabay to find another trapdoor ram card.

doesn't solve my ultimate issue though. a vampire is no going to fit with the megachip board :~( ....

good call on the chip temps though. going to check that now

[Pat the Cat]

If you want to build a new one from a blank board, it can be done.

http://eab.abime.net/showthread.php?t=85395&highlight=A500+RAM
EDIT: Hmmm, extra 512K of chip RAM or a Vampire... no contest. You might lose a litltle compatibility, but you get huge CPU power, and the HDMI output can give you way better resolutions than the native A500 ones.

[darksun9210]

nope. nothing on the chip temps.

got the kids IR temp monitor. so much better than trying to stick a piece of plastic in a wriggling toddlers ear. does surface temps and calcs body temps. so, in surface mode:-

agnus hovers at around 44 deg C when all is working fine.

power off,
switch trapdoor exp on.
power on,
trapdoor ram chips don't warm up. hover at around 19.5 - 19.7 deg C
Agnus however gets up to about 50 deg C?
power off.
switch off trap door ram,
power on.
all ok...

as for the vamp... well.... yeah there is that, but the minimegachip takes me from 0.5 meg chip to 1.5 atm... and that's got to be helpful with WHDload stuff. plus I won't be worried about running out of chip ram if I have to do stuff in native resolutions... maybe if I can get the 1meg chip thing working that'll ease my stress in that regard...

[Oldsmobile_Mike]

doesn't solve my ultimate issue though. a vampire is no going to fit with the megachip board :~( ....

Not sure how it compares size-wise, but I know a Megachip board fits inside an A500 with a VXL*30 accelerator (which is a pretty honkin' big card), just have to use an extra set of riser pins on the 68000 socket.

Might be more tricky with the Vampire because of that IDE header sticking out of the top.  Maybe in conjunction with one of the adapters that brings the 68000 socket further back inside the case?

Have you checked on any of the dev forums?  I'm sure someone who owns this combination can offer some suggestions for getting it to fit.  Good luck!  

[Pat the Cat]

maybe if I can get the 1meg chip thing working that'll ease my stress in that regard...

That's the way I'd run it. But then again, I don't have much need for more than 1Mb chip, and am probably very untypical in that respect.