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

[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.

[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.

[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

[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...

[darksun9210]

Oldsmobile_Mike
that's pretty much what I'm after! with just with the clockport socket adapter on the 68k socket puts the 68k up against the bottom of the keyboard, so need a different shape to move it back, and maybe then over the indiECS.

sheesh, i'm not after much am I

clock port is handy as there is no Ethernet (clockport/usb to Ethernet dongle) solution for the 500 bar a zorro adapter for the side car slot. slow but it works. plus usb sticks are hany for moving large amounts of files around between machines.

used to had SMBFS setup to map network shares as logical volumes on the miggy.

anyway. final concern. I think the trapdoor ram is failing because the trap door trace I've cut as per minimegachip (dis/in)structions is shorting to ground, so I think I may have cut through to the ground plane if there is one on the 500.

or is it actually a ground line? I suspect it should be an address line that switches it from the slowram address range to the 2meg chipram address area, but I cant find any info on what this trace is to fix/repair/circumvent my butchery.

I'm going to give it some pokes with my circuit tester with the trapdoor ram on/off switch to see if I can find what changes between being enable and disabled.

[darksun9210]

aha! that's great info, many thanks rkidd7952! i'll have a poke and a prod this evening and see what is what. either ground, nothing, or 5V - and if connected to pin 32 of gary.

[darksun9210]

ok. update time.
pin32 on Gary seems to be grounded.
pin32 on the trapdoor slot is NOT connected to pin 32 on Gary. so i guess the trace IS cut?

playing with the switch on the trapdoor expansion doesn't seem to effect this trace. no change from looking like a ground line. which would tally up with it being cut?

attached photo of the back of the expansion board.
pin 32 from what I can count is the fourth pin down on the right side from the top of the expansion connector.
this only seems to be connected to the 2nd down on the left side of the DIP chip on the - as you look at it, left side of the board. it's highlighted basicly by the letter "A" in the word RAM on the back of the board.

none of the pins on the switch seem to be connected to that?

secondly, I can't get 5V across pins ten and twenty. but let me double check I've got the right pins, so i'll update in a second when I find that info

(edit - rotate that picture 90 degrees clockwise and what I said makes sense)

[darksun9210]

ok I was being a bit of a bell and measuring between 10 and 11 on the ram chips. now I have the right pins, i'm getting 4.77Volts between 10 and 20. had to confirm that DIPS follow a standard pin pattern.

Marstons EPA is only 3.6% but it's obviously enough to need me to double check my work at the very least.

[darksun9210]

good stuff! I've been after a pin out of the trapdoor slot to be sure
yes I had the wrong pin. I was following the dip pin numbering scheme. I didn't twig it would be the same as an edge connector/card slot.

will test this when I get home tonight

[darksun9210]

Right! Good News!

so, as per your advice, I counted alternating pins till I found pin 32 on the trapdoor expansion. as a bonus, there was a visable trace going from that pin on the trapdoor expansion card to a nice fat solder pad.

checked the continuity between that and pin 32 on Gary.
got a beep for both the ram being enabled, and the ram being disabled on the switch.
crap. ok. kitchen pairing knife, pressed and cut another point on the trace as carefully as I could manage.
no beep this time for either enabling or disabling the ram
test power on.
boots fine. still 1.5meg chip
power off.
enable trapdoor ram module
power on.
hard drive light pulses as the GVP scans the scsi bus.  - excitement! never got this far before!
guru, left click, reboot - worry.
drive light pulses again. - excitement!
boots! oh my god.

take picture as attached.

JOB DONE!

thanks everyone for all your help learnt a lot. I think the main thing was finding what to test to find the problems