unusual 464 black screen..with no lower rom board diag boot..

Started by WacKEDmaN, 09:50, 14 November 22

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WacKEDmaN

ive got a 464 mc002C board im trying to fix..

its black screen boot..sometimes ya can see some flicker..
i cant get lower rom board with diag to run either... ive cleaned the edge connector (it wasnt too bad)

ive tried the usual... z80, crtc, rom.. LS244 and LS32...
(im going to replace and socket LS373 and LS132 aswell)

the board had a 40010 on it.. which has been replaced..
the 40007 slot has also been socketed and tried with same results...

its strange, ive checked the voltage on the board and theres hardly any voltage drop..
im inputing 5.03v and seeing 4.98v at the boards ics.. so power seems good..
im seeing 500mA current draw with 40010 and 800mA with 40007..

last thing is the 153 mux chips.. but.. diag should boot if that is bad right?..
ram wouldnt stop the diag from loading either right?

is it possible for 8255 PIO or the AY sound to stop the boot?...

..on a side note.. i notice these boards are based off the 664 schematic.. the clock chip is a hex inverter while the 464 is a quad nand..

Bryce

Have you tested all the Data and Address lines to see if one of them is held high or low?

Bryce.

WacKEDmaN

ok i guess that will be my next task!.. i didnt think of that one.. thanks Bryce!

WacKEDmaN

turns out original 40010 GA was toast..no clock or rgb out.....its got a new one that seems to be outputting clock and RGB...

so..looks like theres some low signals on some of the data lines..
checked on the ram chips pin 2...
ic120 - D0 = good
ic119 - D1 = bad
ic118 - D2 = bad
ic117 - D3 = good
ic121 - D4 = good
ic122 - D5 = good
ic123 - D6 = bad
ic124 - D7 = bad
(see pics of good vs bad!)

i also checked the signals going IN to the 244...they are also bad.. corresponding to the output..at the ram..

LS373?

or would this be somethin like the PIO pulling the data lines down?

also with these boards...i noticed on the 40007 gate array slot...there is no VCC2..pin 9 and pin 33 is at ground..


WacKEDmaN

Quote from: WacKEDmaN on 06:42, 15 November 22they are also bad.. corresponding to the output..at the ram..
,,that line is a bit lame.. output of 244 goes to gate array...

either way..input of ram and input of 244 both have bad data lines..

WacKEDmaN

anyone got any ideas?? RAM? or something else...

i had a look at a few of the address lines too.. they looking a bit funky too.. most lines are being held high.. and seems only a few of the lines seem to be toggling..

WacKEDmaN

checked around some more...

pulled the crtc and rom chip... and tested the data lines...
some still dont look good...(see pic D2 line)..checked them all over and they are the same everywhere..
..tried a new z80..same deal... the pic attached makes me think maybe its just he LS373...coz only half the data is low...

the address lines are actually fine at the z80...

is this bad ram... or bad elsewhere?!

the 153s couldnt be causing this could they? they are only connected to the address bus, crtc and cas/ras for ram.. they couldnt pull some data down like that could they?...

WacKEDmaN

well.. i bit the bullet and pulled the "bad" ram....

3 out of the 4 of them are toast...

ill pull the rest and socket them tomorrow...

strange thing is...i still cant get the lower rom board to work.. even with that ram pulled...
i even put some solder on the fingers for better contact... the light comes on..but no action...

eto

If any data line is constantly low or high, it won't boot. This can be caused by any of the ICs that is related to the data lines. I had it twice with the ROM. I first thought ROM should not impact it as the external ROM should take over, but since the ROM set one data line to 0, the external ROM could not work either. 

WacKEDmaN

Quote from: eto on 15:15, 16 November 22If any data line is constantly low or high, it won't boot. This can be caused by any of the ICs that is related to the data lines. I had it twice with the ROM. I first thought ROM should not impact it as the external ROM should take over, but since the ROM set one data line to 0, the external ROM could not work either.
ROM has been pulled aswell...lower rom board still didnt boot....all logic major logic changed... the only things left on the data bus are the printer port and the PIO
ill pull the rest of the ram in a few hours n see what happens...

WacKEDmaN

ram has all been pulled... and socketed and replaced with good working chips.. 

but still no boot...and still the bad data on the lines

im beginning to think GA (40010)....
i tried the 40007....but..ZERO activity on the data bus... (40007 needs VCC2 which this board does not have)

but now im actually seeing something on screen on boot (black with blue pixels!)...

...could it still be the 153 mux ICs causing this?... or am i still looking to the PIO or printer port for the data errors?
(lower rom board is now starting to show signs of life.. but colored screens.. no proper boot)

d_kef

Quote from: WacKEDmaN on 14:36, 17 November 22...could it still be the 153 mux ICs causing this?... or am i still looking to the PIO or printer port for the data errors?
(lower rom board is now starting to show signs of life.. but colored screens.. no proper boot)
The 153s can definitely be the problem. I got my 464 on ebay a few months ago and it had a similar problem: sometimes black screen and sometimes lines of pixels. It turned out to have a fried RAM chip and a a fried 153 shorting an address line.

d_kef 

WacKEDmaN

thanks d_kef ...yeah looks like im pullin the 153s next.... 

...if it still does it then its defo PIO or printer port...

WacKEDmaN

got this board working today...
put in the 2 12ohm 1/2w resistors.. and the 40007

40010,153, 244 and a ram bad....

thing is ..it really didnt like mixing the ram after pulling the one bad ram chip it was showing..
i tried my one of my original ram chips, and it failed..
i tried one of my 12ns chips and it also failed...

so i pulled all the ram and put in my 12ns and it worked....
seems all the ram was bad...

WacKEDmaN

heres an update of the board working...
..i fixed it for a mate who was fixing it for a mate!... 
should be back in the hands of the owner soon!...

check out mates channel too.. he does a bunch of vids on different retro systems..alot of soviet clones too..

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