cpc464 no video

Michael1976 · 18:55, 10 March 24

hi im new and dont have a clue on forums ! so just signed up and created a post..... 4 months ago i was at work & picked up a amstrad cpc 464 ! out of a skip along with a monitor !, as a customer of mine was throwing it out !

recently powered up it up and it all worked , except the tape deck ! , so sent tht of to repair mutant caterpiller games !, came back from repair ! put all back together ! loaded manic miner ! after 5 mins being on it crashed ! ? so i restarted the computer ! soon as i powered of and on the home screen flashed on off ! so i did this 3 or 4 ore times till now having a black screen ! , so reading on forums , i had to sign up to an account ! ,, i dont have a scope , im not good on pin outs etc , im on facebook amstradrians ! and had one person help me , so i did the basic tests and still black screen , ive replaced all the rams , and the crtc chip , had a rom reprogrammed , , so basically stuck , the z80 works in my sinclair 48k with no problems ! any one can help ? are there any other logics for video out put , i have now bought a modern psu and scart lead for my lcd monitor ! , also the origanl monitor works and have checked its outputting 5.1v and the screen works !

thanks ,

Bryce · 19:13, 10 March 24

Hi,
you may have done a lot more than was necessary. Have you done the following checks:
- Does the power power switch work? (bi-pass it to check this)
- Have you measured that 5V is getting to every chip?
- Have you checked for dry joints on the monitor socket?
- Do you get a beep when you hold down the DEL button?
- Have you tried powering it up with the tape deck disconnected? (you need to jump some pins for this as the power switch is on the same connector)

Bryce.

Michael1976 · 19:24, 10 March 24

Hi
Bryce thanks for the quick reply ,
Power switch working cleaned it ,
Power led works comes on,
Yes , I by passed the wires , as told from a member ,
Plugged in cassette deck pressed delete no beep ,
With volume up ,
Power input jack I measured the voltage and was 5.0v,
I also replaced the video connector the other day and forgot to mention tht earlier sorry about tht ,
When I bypass it with wires , always says no signal, even with monitor and lcd ,
I will try and upload some images of the board its a early revision

Regards,

McArti0 · 19:36, 10 March 24

Photo Mainboard and what's GA have You 40010, 40008 or 40007?

ps. Meaning. What GA did you have?

Michael1976 · 19:42, 10 March 24

It's a 4007 ga

How do I upload fotos ?
Please

Mother board is mc0002b

Thanks

McArti0 · 20:01, 10 March 24

such a motherboard?

https://www.cpcwiki.eu/imgs/5/52/CPC464_PCB_Top_%28Z70200_MC0002B%29.jpg

McArti0 · 20:27, 10 March 24

For 464 mc0002b and 40007
Join GA pin 10 and down side R114 resistor. You can hear in Speaker 300Hz interrupt signal
next
Join GA pin 15 and down side R114 resistor. You can hear in Speaker 50Hz Vsync signal from CRTC
next
Join GA pin 11 and down side R114 resistor. You can hear in Speaker ~50Hz vsync signal out from GA.

Michael1976 · 20:55, 10 March 24

hi wont have a clue on how to do tht just yet my friend ,
thanks

that is the mother board as well ty

Michael1976 · 20:55, 10 March 24

Quote from: McArti0 on 20:01, 10 March 24such a motherboard?

https://www.cpcwiki.eu/imgs/5/52/CPC464_PCB_Top_%28Z70200_MC0002B%29.jpg

yes
ty

Michael1976 · 21:06, 10 March 24

hi i cant seem to load any photos of the board ! says session time out

thanks

McArti0 · 21:24, 10 March 24

3 simple probe.

McArti0 · 21:29, 10 March 24

Tell me, was there a metal radiator on 40007?

Michael1976 · 21:39, 10 March 24

yes there was ! but broke when removed there was thermal grease all over the place ! i still have the rest of it ! just the bracket under neath it on the left side where it clips in , i will get it refebricated at somepoint , if i get the computer going again , i still cant understand fully working then crashed after 5 mins and kaput !

thanks

McArti0 · 21:45, 10 March 24

Probs. Do it. Do it now.

Michael1976 · 23:00, 10 March 24

Ok , will do at somepoint tommorow , set meter to dc , ?

McArti0 · 06:40, 11 March 24

DC A

SerErris · 18:40, 13 March 24

Quote from: Michael1976 on 21:39, 10 March 24yes there was ! but broke when removed there was thermal grease all over the place ! i still have the rest of it ! just the bracket under neath it on the left side where it clips in , i will get it refebricated at somepoint , if i get the computer going again , i still cant understand fully working then crashed after 5 mins and kaput !

thanks

Did it work before you removed the heat sink or after? So did you let it run for 5 minutes without the "cooler" ? It is getting very hot without it. Not sure if that is getting it in danger to die.

Michael1976 · 18:51, 13 March 24

yes it worked for 7 mins, overall,,,,,, its not broken im positive the fault lies somewhere else it was working perfectly turned of then on basic flashed up 2 seconds then of repeated 2 or 3 times then kaput !

mike ty

McArti0 · 20:35, 13 March 24

In monitor is short circuit protection. Is there 5v on pin 16 of 74LS153?

Michael1976 · 23:16, 13 March 24

Hi I will che k. Tommorow, I got a picture earlier,,,
This evening, blue back ground but black text , then picture dissappear, stays for 5 to 6 seconds then if I turn it off and on nothing , if I wait a further 6 to 7 mins same again , I checked some voltages on rom and crtc chip I've got 4.9v , and ram also 4.9v

Can check the other chip tommorow , seems like computer losing video sync

Mike ty

McArti0 · 12:25, 14 March 24

Quote from: McArti0 on 21:24, 10 March 243 simple probe.

Bryce · 22:02, 15 March 24

Do you have a different TV you could test it with?

Bryce.

Michael1976 · 23:20, 15 March 24

Hi bryce ,,
I have already done tht ,, same , the image came back blue background with green and red text then dissappears after 6 seconds , until I turn of and on again ,

Ty

McArti0 · 00:37, 16 March 24

Do you have a heatsink on the 40007 now?

Have you done these 3 simple tests?

What voltage do you have on pins 2,4,7 and 40?

McArti0 · 14:42, 16 March 24

voltage CPC after swith on (The table is helpful when you don't have an oscilloscope. And all you have is a voltage meter/multimetr)

Code Select

            GA 40010    GA 40007
----------------------------------
CCLK       ~1,2V pin4     pin40

RAS        ~0,9V pin34    pin7

RAMRD      ~3,5V pin29    pin13

nCPU       ~2,5V pin14    pin1

ROMEN      ~2,8V pin27    pin12

PHI        ~2,1V pin19    pin39

READY      ~1 V  pin 22   pin2

244en      ~4,5V pin 23   pin4

      Z80
---------------------
A15    ~1V    pin5
A14    ~0V    pin4
A13    ~1V    pin3
A12    ~2,1V  pin2
A11    ~2V    pin1

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cpc464 no video