464 Resurrection - with only mainboard!

[robcfg]

How are you powering the board?

[WacKEDmaN]

powering the board with a small CV/CC power supply i use for all my micros n what not, 5v exactly at the barrel jack on the board..has voltage and current draw displays so i can see whats being used..

heres the clock on the scope.. (with "phosphor" on to sorta help..)..i see no squares!
..at pin 12 of the quad nand...

You cannot view this attachment.

and here is leg of R141 (out of the opamp..to z80)..its just lower on pin 39 on the gate array..

You cannot view this attachment.

[WacKEDmaN]

the CRTC pin 21 is generating a nice square-ish wave..

...im going to replace the LS153s, the 244, 373, 32 and the 00, later today if i can get over to the shop..i cant get the others locally unfortunately..

[robcfg]

How much current can your power supply give?

I think around 2 amps should be good but you'll need more if you add expansions.

[WacKEDmaN]

How much current can your power supply give?

I think around 2 amps should be good but you'll need more if you add expansions.

3Amp... 5 with better cooling!
i noticed all the main chips getting warm, gate array, z80, crtc, pio..are all a bit warm..

[WacKEDmaN]

so i changed the 4 LS153s, the 244, 273, 373, and the 00..
the last 3 LS chips will need to be ordered from somewhere...
...and same result...(i think my scope cant keep up with the clock..CRTC is puting out nice square waves.)
no activity on the bus..(low this time)

im really stumped.....
i guess i could order a new AY, and PIO...and new CRTC for good measure..
...maybe a rom burner aswell...

[WacKEDmaN]

seems i cant get an ay, ppi, or crtc in the country...SMH...good old parts shortage...

what should i be checking for next...? ..could it be ram/rom?..if i pull all them, it should just nop right? so i should see activity on the address bus...
or should i be checking something else on the gate array?
should i pull the rom and try to read it with an arduino?
maybe i should pull TR2 and replace it with the original?..(altho that shouldnt stop bus activity)

not sure where to go next.. some help would be appreciated..

[WacKEDmaN]

ordered the LS32,LS132 and LS145...should be here in a coupla weeks knowing auspost!

ive got a funny feeling its LS132 or LS32.. LS132 would make sense being part of the reset circuit..

[tjohnson]

so you had a board a couple of years ago, now you have a different board but that doesn't work either, tbh not sure what it say.

[WacKEDmaN]

so you had a board a couple of years ago, now you have a different board but that doesn't work either, tbh not sure what it say.

yup...its that bad!..ive been at this about 18months now...
..old board i purchased online cheap.. missing the gate array.. sourced one from Tot0 here.. no boot..
i was playing around with it and pushed down hard on the CRTC and got a screen..but looked like bad ram..never has it booted again!...
tryed replacing CRTC..killed the board..damaged tracks and ripped out almost every via on the CRTC :/
...so waited till these new boards where available..soldered it up.. looked good.. put chips in..nothin.. tried replacing most of the logic, the ram is also new..crtc is new..

could only be the ROM..the 8522, the AY-3, a bad CRTC..or hate to say it..bad gate array..
..i dont have a rom burner, or any rom boards like dandanator etc.. so im flying blind!... i do have sillyscope.. but its crap! wont read the 16mhz clock,  4 and 1mhz is fine..

other than replacing the logic i havent replaced yet.. im stumped where to go next...

[tjohnson]

What are you trying to achieve?  Maybe you can send the board to Bryce to diagnose and get working.  I'm assuming the board is actual known working i.e. not a development board where there could be faults.  Tbh it would have been easier to find a working machine i would think rather than trying to build a new board.

[WacKEDmaN]

What are you trying to achieve?  Maybe you can send the board to Bryce to diagnose and get working.  I'm assuming the board is actual known working i.e. not a development board where there could be faults.  Tbh it would have been easier to find a working machine i would think rather than trying to build a new board.

just trying to get a working cpc!..
this is the board ive after it was tested and faults found and fixed..
https://www.tindie.com/products/bobsbits/amstrad-cpc464-replica-pcb/

and ..im in australia..so im not really fond of sending it out of the country...i waited a month for the new board to arrive..

[WacKEDmaN]

so i bumped up the voltage on my power supply to 5.6v... chips now getting 4.9v.. but still no boot

[Bryce]

24MHz is definitely not enough bandwidth to measure a 16MHz square wave. I've a post here which will explain why: https://www.cpcwiki.eu/forum/amstrad-cpc-hardware/understanding-retro-electronics/msg144677/#msg144677

Bryce.

[WacKEDmaN]

yes Bryce..that was what i thought!... Nyquist says you need atleast double the bandwidth of the frequency youre trying to measure.... the clocks out of the gate array look fine so im going to assume the 16mhz clock is fine too...

got the last of the logic chips today.... and still nothing...
not even a black screen signal.....

so..thats gotta be gate array or CRTC right?!

ill order another CRTC... but...if its gate array..im guessing im screwed until the chip is reengineered....

i did notice the 3 new logic chips increased the current by almost 100mA... it pulled 1A on first boot with the new chips but dropped to 970mA shortly after...

[dragon]

I know that sensation... You have a computer that cost cheaply and you want it work and you begin buy buy and buy pieces because nothing work and at finish you spend 10x more  money that another cost on eBay or similar.

I'n your case the 464 are the more cheaply.. Maybe os better search another and then you can swap ics?. 

But well,you have here a gate array spares.

https://www.icompplus.com/es/circuitos-integrados/12619/40010

https://www.icompplus.com/es/circuitos-integrados/32243/40007

I have not buy there... But they are in my city. I can made a order there and pickup it in person. 

[WacKEDmaN]

I know that sensation... You have a computer that cost cheaply and you want it work and you begin buy buy and buy pieces because nothing work and at finish you spend 10x more  money that another cost on eBay or similar.

I'n your case the 464 are the more cheaply.. Maybe os better search another and then you can swap ics?.

But well,you have here a gate array spares.

https://www.icompplus.com/es/circuitos-integrados/12619/40010

https://www.icompplus.com/es/circuitos-integrados/32243/40007

I have not buy there... But they are in my city. I can made a order there and pickup it in person.

yup its a bit like that!... but i havent really spent all that much trying to get it working (thats if you dont count the new black board!)...all the logic only cost about $20.. got the gate array from user here for like 20$ with postage..CRTC was coupla $... the original board was purchased very cheap as it was missing the gate array (and obviously had other issues!)
thanks for the links ... i'll check them out....

i finally got in contact with a local who has a complete CPC collection....so i maybe able to swap some chips over between his boards and mine to test...

[WacKEDmaN]

yay! finally some signs of life!
got a hold of a lower rom board with diagnostics... plug it in..fire up the cpc.. hit the reset button... and i get a screen!..albeit corrupted!

You cannot view this attachment.

this is with the original ram chips... ill drop my new ones in and see what happens....

its really looking like the rom is the whole issue with my board....

[Audronic]

Throw the left hand switch to the other position
With the the Computer turned off
Power up and tell us what  happened
 
Keep Safe

Ray

[WacKEDmaN]

Throw the left hand switch to the other position
With the the Computer turned off
Power up and tell us what  happened
 
Keep Safe

Ray

...still with the original ram...

You cannot view this attachment.
 
i guess i need to start working on my ps2 keyboard through arduino if i wanna test some more! (or atleast workout which pins to hit to fake a keypress!)

EDIT: i tryed rebooting Noels rom and now i just get corruption cant read anything... interesting...

[WacKEDmaN]

well this is a bit strange....
i dropped the "new" ram chips in and just got corruption....
i removed 1 ram chip (top left)... and now i get the ram tester screen....
its saying chip 3 is bad... even tho, what im presuming is chip 0 is missing!

what is the layout for the chips on the ram tester??

You cannot view this attachment.

[Audronic]

Can you send us a Photo of the Motherboard

Noels diag photo said " 128K ram" ?

Ray

Edited Removed NO FDC

[Audronic]

464 Ram Location

Bit 

0 IC 120
1 IC119
2 IC 118
3 IC 117
4 IC 121
5 IC 122
6 IC 123
7 IC 124
-================-
121.   117

122.   118

123    119

124    120
-================-

Ray

[WacKEDmaN]

yes i thought the 128kB was a bit strange aswell...theres a pic of the board on page 1...
thanks for the ram location.. i ended up working it out after testing one chip through all the sockets..

i havent been able to get back to that diag screen (Noels)..

i keep getting corruption.... UNLESS i remove chip 3 (top left ram chip)...then i get the ram tester screen...
ive tryed that chip in other slots and it is green... no matter what ram chip i use in slot 3 just causes corruption (they are all showing green in other slots)

i tried taking one ram chip and running it through all slots on its own... some slots would make the colors change (eg purple instead of green)..one would show a few green lines in the correct area but none of the numbers or other lines show...
....thats probably CRTC correct?

edit: heres a pic of the tester with no ram... is that dotted line between 0 and 1 supposed to be there?!
You cannot view this attachment.

edit2: heres the current setup....
You cannot view this attachment.

[Audronic]

i keep getting corruption.... UNLESS i remove chip 3 (top left ram chip)...then i get the ram tester screen...
ive tryed that chip in other slots and it is green... no matter what ram chip i use in slot 3 just causes corruption (they are all showing green in other slots)

Ok I would check the "Chip 3 Soldering for Perhaps shorts to ? " and have a good look at Pins 2 and 14

Good luck

Ray