LC475 with no video

[falen6]

Hi all

recently got me an LC475

battery did not leak

caps did

removed old caps and solder - scrubbed board - recapped with tants

power on gives good chime but no video display

have tried different vram pairs , tested on another machine

have tried different ram sims , also known to be good

still no video

when i add a ram simm i get bad chime , so thinking ram problem

then i pressed on first onboard ram chip next to c128 and c127 and hit the power , i get very fast chimes of death

i dont press on anything and i get good startup chime

c127 and c128 ( along with all the other caps ) leaked all over the place

the board has been thoroughly cleaned over and over with iso , acetone , ..... even boiling water !! - still no video

also - when i add ram expansion i always get chimes of death

so im thinking it is the onboard ram , bad pin / pad / trace connectivity

I have already reflowed all the onboard ram chip pins , still no video

If I have an onboard ram problem how come I am getting a good chime

also - even thought i have no video output I think the computer is crashing after the good chime as it will not boot from floppy or reboot when doing the command, option , p , r reset - nothing

i DONT have a pram battery installed ( have to get one ) but even the quick off and back on trick yields no video

im thinking of using hot air to take off the ram chips next to c127/128

just wondering if anyone has had similar issue

cheers

 

[Realitystorm]

I never had any luck with the quick on and off, I only get video with the pram battery installed

 

[falen6]

I never had any luck with the quick on and off, I only get video with the pram battery installed

thanks storm

i have a 3 volt dc power adapter - u rekon it would be ok to wire that into the battery holder terminals just to see ? , just to test it

i really dont want to blow this up !!!!

 

[falen6]

also - i have tested the power , even swapped out the psu from my working lcIII , thats where i swapped the simms just to see

they all come up good

 

[shirsch]

From my experience a battery is required in order to get video display.

 

[croissantking]

I’ve had good results with quick on and off.

 

[falen6]

ive ordered up a few of those 'macbatt' things

i had a 475 before and the quick on/off/on always worked for me as well

who knows

maybe its part of the startup sequence , that if the video is not initilized the start up freezes

 

[Juror22]

From my experience a battery is required in order to get video display.

Ditto on the battery with this model. And I have much better luck since I started using a white vinegar soak to eliminate the cap juice (followed by DI water and 99% alcohol) for what its worth.

 

[falen6]

well , just tried it with a 3 volt battery and still no video

good chime

no video

does not try boot from good floppy in a good floppy drive

it appears to chime and then just freeze

as i said before , i got this , battery removed , no sign of any acid damage , caps leaked but no bad signs of the usual corrosion from electrolite

its even chiming now with the ram extension installed - im using 2 good vram simms

but no video

have not seen a video display on this since i started working on it

ill try the vinegar both sides , see if that helps

has to be something stupid !!!

 

[falen6]

tried the vinegar bath ........ no change - let it soak for an hour

why is this machine giving good startup chime , but no video .. zip ..... nada

anyone know of the chips/ traces that could be at fault

from the condition of the board ( very very good ) it has to be something close to the old caps that leaked .......... or im jinxed and their is a dead chip or something on here

kinda giving up here

 

[croissantking]

Ooh that’s a tough one to diagnose.

If I had to guess I’d say broken trace rather than bad onboard RAM, maybe you could tone out the traces between the memory controller and the RAM.

 

[Juror22]

well , just tried it with a 3 volt battery and still no video

What was your arrangement for this? The normal lithium battery (14250) is 3.6 volts.
I will test out mine with a lower voltage and see if there is a point where I can recreate the issue.

Alternatively if it is a broken trace, here are the 475 schematics from the MacDat site (nice place btw). I don't know where to direct you next, hopefully someone else does?

 

[croissantking]

What was your arrangement for this? The normal lithium battery (14250) is 3.6 volts.
I will test out mine with a lower voltage and see if there is a point where I can recreate the issue.

Alternatively if it is a broken trace, here are the 475 schematics from the MacDat site (nice place btw). I don't know where to direct you next, hopefully someone else does?

Presumably a CR2032 as OP mentioned Macbatt. This should be fine as I run one of my LC475’s (as well as several other vintage Macs) like this.

 

[falen6]

i have ordered the macbatt - so in the mean time to test it i just soldered 2 x 1.5 batteries - gives 3.12 volts - thats good enough to test it , made no difference

the fact that the machine is not booting from the floppy ( known good disk and drive ) tells me the machine is stuck / crashed

if it was just a video issue the machine should start booting from floppy , even with no video i would hear it reading the floppy

i dont think the 475 can create a video signal without a pair of vram simms installed

i have tested the pair of vram that came with the machine on my lciii and thy work fine

on my lcIII i turn it on , there is a delay , then the chime , then about 2 seconds later the video signal is output

at a guess would the startup be something like , power on , self test , test ram , chime , test vram , initilize video , boot ?

i get as far as chime so im thinking the machine is getting stuck testing vram - ill have to start checking traces

thanks for the schematics Juror