464 Resurrection - with only mainboard!

Started by WacKEDmaN, 19:35, 09 December 20

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WacKEDmaN

so ive got the original 464 board completely populated now...
i only have the board.. no monitor, no keyboard, no tapedeck.. im gonna add my own digital versions with overpowered arduino and/or esp32
i will use this thread to document my progress and ask a few questions (so i dont blow it up!)


i need some clarification on the power jack... i cant find the correct information, is it "centre negative" or "centre positive"...
ive done a continuity test...between the side pin of the barrel jack socket (onboard)... and both the AY-3 (pin 3) and Z80As (pin 11) 5v pins... and they seem connected...
but everything ive read is saying the 5v jack is centre positive.. even tho im seeing different on the board...
can anyone clarify it for me please?... (or should i just give up now! LOL)


next no so much a question but my next steps...... i have a SCART to RF modulator.. with female scart in...
i found this... http://www.cpcwiki.eu/imgs/c/c1/Cpc_to_scart.png
i will be wiring the 464 board directly to the scart pins on the RF board (in reverse! female din to female scart)...

heres the current look....



TotO


Center is positive for 5V and GND is outside... Just check the ground continuity with other connectors.
You can test the 74LSxx IC where the bottom left pin = GND and the top right pin = VCC. (not the RAM)
"You make one mistake in your life and the internet will never let you live it down" (Keith Goodyer)

WacKEDmaN

#2
thanks ToTO, ill wire up the scart and kick it in the guts...
hopefully theres not other issues on the board...i hope i dont have to break out the sillyscope!


it does seem a bit strange the side pin on the barrel jack socket is connected to 5v positive on the main chips.. and the one coming from the centre is neg... yet it seems swapped from the actual 5v plug... all the other barrel jack sockets ive played with are outside to side pin, and then centre to centre... this seems swapped :/
i guess theres some inverse logic going on here...

tested side pin on the barrel jack socket to bottom RIGHT pin of the 74LS132p and they are indeed ground... (i looked up the datasheet!)



im confuse! ..but ill work it out! (ahh im workin from the top of the board!.. flip it..and yes bottom left is gnd ..top right is pos!)

gerald

Quote from: WacKEDmaN on 19:54, 09 December 20
thanks ToTO, ill wire up the scart and kick it in the guts...
hopefully theres not other issues on the board...i hope i dont have to break out the sillyscope!


it does seem a bit strange the side pin on the barrel jack socket is connected to 5v positive on the main chips.. and the one coming from the centre is neg... yet it seems swapped from the actual 5v plug... all the other barrel jack sockets ive played with are outside to side pin, and then centre to centre... this seems swapped :/
i guess theres some inverse logic going on here...

tested side pin on the barrel jack socket to bottom RIGHT pin of the 74LS132p and they are indeed ground... (i looked up the datasheet!)



im confuse! ..but ill work it out! (ahh im workin from the top of the board!.. flip it..and yes bottom left is gnd ..top right is pos!)
As far as I know, the plug is positive on centre pole unless you have a very rare version of a 464. :D
How do you check continuity from jack center to the IC pins ?
5V should no go straight from the plug to the ICs. You have to do a short on the tape connector, where the power switch is connected.


WacKEDmaN

#4
oh yeah! that probably explains why im having issues!... ive got the board sitting on the bloody silver side of the cardboard shield!


now im not getting continuity on the centre to the 5v in on the 74LS chips even with the switch connector bridged :/
(i was forgetting the switch! thanks for the heads up Gerald!)


...it looks like i know enough...just to be dangerous! LOL


WacKEDmaN

#5
hooked up scart..and powered up the board..


..and nothing.. seems to draw about 0.9Amp and there seems to be activity on the z80 buses.. (checked with oscilloscope..)
...need to checked voltages ..seems to be 4.3v on everything..

CRTC chip (HD6845SP)seems to be getting warm after a few minuites.. (ram very slightly).. is it known to get warm to hot? (its not burning hot!)


seems to be working..i just cant get a picture  ::)
..i might invest in a cga/ega to vga board...the scart to RF modulator is horrible, i plugged wii into it to make sure it works..
..ok thats ordered.. should be here by the end of the year if im lucky!  :)



WacKEDmaN

#6
so the EGA/CGA to VGA board arrived today...
wired it up (soldered to the pins on bottom of cpc board)... this board and pinout.. https://www.octoate.de/articles/connect-cpc-to-vga-display/


but still no picture...

Question: does the cpc "need" anything else connected on boot? like does it look for the tape drive or keyboard? im guessing not
i cant test the the board is working (just no pic) with no speaker or keyboard! (cant hit esc/delete to beep!)... i suppose i could hook up an amp and speaker to the headphone jack.. but bit hard to make a keyboard from an arduino without the display showing!

next step is to replace the Z80... i tryed it on a bread board and it was doing weird things on the bus.. (would stop increasing the address bus after a few cycles just doing nops..should continue increasing right?)
be a few more weeks before ill get my hands on them tho with xmas and new years 

Bryce

#7
The CPC Mainboard will run with nothing attached accept the power cord. You would need some test equipment to know whether it's running or not, so it easier to have it connected to a display at least.

Bryce.

WacKEDmaN

thanks Bryce
i do have an oscilloscope.. (guess i need a logic analyser)..
not sure what i should be looking at!.. i am seeing activity on both the data and address buses on all the main chips..and the logic chips seem to be all be working...


but like i said i think the z80 maybe bad..so im going to replace that first..
...another month before i get to move on!..unless someone has some ideas for me! :P

Bryce

What are you getting on pins 39 and 40 of the CRTC?

Bryce.

WacKEDmaN

#10
[screwup]... this is pin 40 of the CRTC (pin 39 looks the same) with just the power connected, no jumper between pin1 and 3 on the tape connector (power switch)..power supply says no current!
when i do jumper it, it remains the same... just triggering more often ... and showing about 90mA current usage on the power supply...[/screwup]

ermagherd im dumb!.. i scoped the clock pin!..and the power supply was too close inducing the ripple onto the signal.... SMH...told ya im dangerous! LOL

... ok next attempt!... this is the real pin 40..
it seems its triggering vsync every half second or so...that doesnt sound right.. should be with every frame drawn right?..

10ms timebase..





here it is at 500ms timebase..






for pin 39 - hsync...its looking much better..
200us timebase!


WacKEDmaN

#11
it also seems the CRTC is the hottest IC after having it running for about an hour..its much warmer than the 40007 gate array...
..im gonna order a CRTC chip and some z80s... cant hurt to have spares!..


also grabbed a 6pin din today..so ill rewire the EGA to VGA board to make things a little nicer..


edit.. so after some reading i find this..
Quote"The standard monitors on the Amstrad (GT6x, CTM64x, CM14 or even TV) have a 50Hz Vertical refresh rate (meaning that a VSync pulse must appear every ~20ms, 19968μs exactly) and a 15625Hz Horizontal refresh rate (an HSync pulse every 64μs). Of course they can usually tolerate some slight variations of these timings but each monitor has it's own limitations."
it seems the vsync timings are a bit off on my board?!

Bryce

If you probed properly and that's the output of pin 40, then the CRTC has an issue. The signal levels are too low too. But just to be 100% sure: What scope are you using?

Bryce.

WacKEDmaN

cheap hantek 6022be...


thanks Bryce.. CRTC will be socketed and replaced..aswell as the z80 replaced for good measure!

WacKEDmaN

so got the new CTRC and Z80s today..
...removed the old CTRC IC..and put a socket in..
fired it up...
and same..no sign of video.....altho all the chips seem to be getting hotter now....ill have to check on oscilloscope later...


...i think im in over my head  :doh:


WacKEDmaN

#15
so ive had a bit of a look around the CRTC with a continuity tester....


seems i killed some vias ripping the old chip out and puttin the new socket in... now i gotta rip the socket out (and possably destroy more vias) and wire the bastard up!
...im thinking i might make a "floating" chip! (wires outta the board to the socket) coz fixing it with the socket in place is gonna be a PITA!


i wonder if it would be cheaper (labour wise), easier, and nicer in the long run, if i was to redesign the board to make it smaller.....
...or...
should i just stop now and send this to someone i know can fix it!? would make a nice vid for a youtube channel!:P

(llopis im looking at you!)

WacKEDmaN

YAY! i finally got some output!

i pushed down hard on the CRTC... and it booted!.. i guess i need to touch up the solder joints!


but that said... it look like there is ram issues...
i get either a gray screen with blue border, or corrupt colored pixels on screen...


im correct thinking this is the ram right?

Bryce


WacKEDmaN

thanks Bryce..


...more waiting for parts...


WacKEDmaN

..im back!.. with the fix to my issues! ;D 
You cannot view this attachment.

i should have it going in a few hours..then i have to make a keyboard for it! :P

WacKEDmaN

powered it up.. no boot... its pulling 700mA... which seems a bit low? (usually around 800mA on boot right)..
checked chips and they all seem to be getting about 4.3v... time to setup the oscilloscope again....


robcfg

Maybe check the diodes orientation.

You should be getting 5v not 4.3, and that 0.7v difference is the same as the usual diode voltage drop.

WacKEDmaN

#22
tried the diode..no luck..(band at the top of the board right?)
i may have the transistors installed wrong.. i used the new ones that came with the board..
my shitty scope is showing 8mhz out of the xtal...(again a new 16mhz)... and it looks horrible.. it seems to be very low voltage wise too..
the clock on the z80 and gate array seems to be just under 4mhz... but its not square.. (dont think its my shitty oscilloscope)...theres no activity on the z80 bus either..
i may remove the original transistors and try them...

...i suck at desoldering/removing components.. ...the whole reason i got this board! LOL

edit:
https://pdf1.alldatasheet.com/datasheet-pdf/view/2827/MOTOROLA/2N2369.html .. hard to tell which leg is which..
it seems i may have got the collector and base around the wrong way.....check and double checked..and rechecked..and its installed right!..

Bryce

The clock signal will never be a perfect square as shown in textbooks. It will always be rounded and the lower the bandwidth of your scope, the worse the signal will look. However, it doesn't need to be a perfect square, all that matters is that it's there and passes a certain threshold on each cycle. The 4.3V is a bigger issue. You need to find out where the other 0.7V is being lost.

Bryce.

WacKEDmaN

#24
thanks Bryce...
it use to be 4.3v on original board aswell..... do you think i could possibly have a bad logic chip somewhere? (i havent got a tester)
..i guess i could pull one chip at a time and see when the voltage goes up!

my scope is still the hantek6022BE...only 24Mhz bandwidth but should be plenty... the clock signal out of the gate array looks nothing like it does in Noels youtube vid... its the same at the nand gates and at the crystal (just lower voltage. i even changed that back to the original!)

...ive changed Ram, CTRC, and z80.. so really theres only the logic, AY, PIO, and ROM that could be bad..

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