C128 problem

classic Classic list List threaded Threaded
3 messages Options
Reply | Threaded
Open this post in threaded view
|  
Report Content as Inappropriate

C128 problem

traymond
The issue with my C128 I found the 
Regulator output I read with a multimeter 
had zero volts.

I asked Ray Carlsen by email he said there's a component shorted
(somewhere).  😂
The safest way is to unplug the power source
Instead of applying power set multi meter on OHM's
I selected the buzzer 
Use a good ground, touch the positive probe on the output side of regulator
I could just barely hear a click from the buzzer which indicates a component is
shorted.
I then removed all socketed chips one at a time checking for the short
but all chips seem okay.
I checked all the caps in the power part of the MB, down towards the power regulator are two smaller tiny caps, one there after I desoldered it finally cleared the
short,  I think the location is C111
I tack soldered tiny cap in and it definitely reads shorted to GND.

So far this looks like the culprit but I'm renewing all the power related caps.
Amazing one tiny little cap could cause all this trouble.

I'm assuming this short fried the VIC chip, I pulled it out and plugged it into a working C128DCR the screen when powered up had a snowy appearance only.
I have 2 other C128 Vic chips they are good Vic chips.

Anyway I did learn how to find a shorted component but finding the right test points
helps.

Will let you all know how this turns out, most if you steered me In the direction of 
the Caps thanks.

Terry Raymond
Reply | Threaded
Open this post in threaded view
|  
Report Content as Inappropriate

Re: C128 problem

william degnan
hope you get this fixed
Bill

On Fri, Jul 21, 2017 at 12:31 PM, Terry Raymond <[hidden email]> wrote:
The issue with my C128 I found the 
Regulator output I read with a multimeter 
had zero volts.

I asked Ray Carlsen by email he said there's a component shorted
(somewhere).  😂
The safest way is to unplug the power source
Instead of applying power set multi meter on OHM's
I selected the buzzer 
Use a good ground, touch the positive probe on the output side of regulator
I could just barely hear a click from the buzzer which indicates a component is
shorted.
I then removed all socketed chips one at a time checking for the short
but all chips seem okay.
I checked all the caps in the power part of the MB, down towards the power regulator are two smaller tiny caps, one there after I desoldered it finally cleared the
short,  I think the location is C111
I tack soldered tiny cap in and it definitely reads shorted to GND.

So far this looks like the culprit but I'm renewing all the power related caps.
Amazing one tiny little cap could cause all this trouble.

I'm assuming this short fried the VIC chip, I pulled it out and plugged it into a working C128DCR the screen when powered up had a snowy appearance only.
I have 2 other C128 Vic chips they are good Vic chips.

Anyway I did learn how to find a shorted component but finding the right test points
helps.

Will let you all know how this turns out, most if you steered me In the direction of 
the Caps thanks.

Terry Raymond

Reply | Threaded
Open this post in threaded view
|  
Report Content as Inappropriate

Re: C128 problem

traymond
Hey Bill,
Thanks  yes been having more fun learning and fixing.☺

This looks to be promising after I found this nothing else seemed to be shorted
finally.
I had to replace the Monitor cable socket the cable plugged In way too hard
so that's hopefully fixed too.

Fingers crossed 😂

Terry Raymond

On Jul 21, 2017 11:00 AM, "william degnan" <[hidden email]> wrote:
hope you get this fixed
Bill

On Fri, Jul 21, 2017 at 12:31 PM, Terry Raymond <[hidden email]> wrote:
The issue with my C128 I found the 
Regulator output I read with a multimeter 
had zero volts.

I asked Ray Carlsen by email he said there's a component shorted
(somewhere).  😂
The safest way is to unplug the power source
Instead of applying power set multi meter on OHM's
I selected the buzzer 
Use a good ground, touch the positive probe on the output side of regulator
I could just barely hear a click from the buzzer which indicates a component is
shorted.
I then removed all socketed chips one at a time checking for the short
but all chips seem okay.
I checked all the caps in the power part of the MB, down towards the power regulator are two smaller tiny caps, one there after I desoldered it finally cleared the
short,  I think the location is C111
I tack soldered tiny cap in and it definitely reads shorted to GND.

So far this looks like the culprit but I'm renewing all the power related caps.
Amazing one tiny little cap could cause all this trouble.

I'm assuming this short fried the VIC chip, I pulled it out and plugged it into a working C128DCR the screen when powered up had a snowy appearance only.
I have 2 other C128 Vic chips they are good Vic chips.

Anyway I did learn how to find a shorted component but finding the right test points
helps.

Will let you all know how this turns out, most if you steered me In the direction of 
the Caps thanks.

Terry Raymond

Loading...