C128 problem

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C128 problem

traymond
Hi,
My C128 has a problem with blowing the fuse in the power source what could cause this?

This C128 is dead, black blank screen, C64/C128 modes won't work, nothing 
She's completely dead.

I was told to check all logic chips, can this be done with a meter or logic probe, does this require and voltages on Logic chip pins?

I found jnfo on how to build a simple logic probe, maybe a different post later since this 
Has something to do with TTL/CMOS LOGIC OR LS logic, very interesting.

Terry Raymond

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Re: C128 problem

Mike Stein

I assume the fuse does not blow when the supply is disconnected from the computer? Voltages OK?
 
Relatively unusual that a chip would blow the fuse; I'd check the caps first, especially any tantalums.
----- Original Message -----
Sent: Thursday, May 25, 2017 2:38 PM
Subject: C128 problem

Hi,
My C128 has a problem with blowing the fuse in the power source what could cause this?

This C128 is dead, black blank screen, C64/C128 modes won't work, nothing 
She's completely dead.

I was told to check all logic chips, can this be done with a meter or logic probe, does this require and voltages on Logic chip pins?

I found jnfo on how to build a simple logic probe, maybe a different post later since this 
Has something to do with TTL/CMOS LOGIC OR LS logic, very interesting.

Terry Raymond

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Re: C128 problem

Francesco Messineo
On Thu, May 25, 2017 at 9:11 PM, Mike Stein <[hidden email]> wrote:
> I assume the fuse does not blow when the supply is disconnected from the
> computer? Voltages OK?
>
> Relatively unusual that a chip would blow the fuse; I'd check the caps
> first, especially any tantalums.

I have a 6569R1 that instantly blows the fuse on a C64 (this chip gets
+12V and +5V from a separate 7805 inside the C64).
But I agree, it's best to first test capacitors. Even a bypass ceramic
could get shorted.

Frank

>
> ----- Original Message -----
> From: Terry Raymond
> To: [hidden email]
> Sent: Thursday, May 25, 2017 2:38 PM
> Subject: C128 problem
>
> Hi,
> My C128 has a problem with blowing the fuse in the power source what could
> cause this?
>
> This C128 is dead, black blank screen, C64/C128 modes won't work, nothing
> She's completely dead.
>
> I was told to check all logic chips, can this be done with a meter or logic
> probe, does this require and voltages on Logic chip pins?
>
> I found jnfo on how to build a simple logic probe, maybe a different post
> later since this
> Has something to do with TTL/CMOS LOGIC OR LS logic, very interesting.
>
> Terry Raymond
>

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Re: C128 problem

traymond
Hi Thanks gives me a starting point.

Terry Raymond

On May 25, 2017 12:50 PM, "Francesco Messineo" <[hidden email]> wrote:
On Thu, May 25, 2017 at 9:11 PM, Mike Stein <[hidden email]> wrote:
> I assume the fuse does not blow when the supply is disconnected from the
> computer? Voltages OK?
>
> Relatively unusual that a chip would blow the fuse; I'd check the caps
> first, especially any tantalums.

I have a 6569R1 that instantly blows the fuse on a C64 (this chip gets
+12V and +5V from a separate 7805 inside the C64).
But I agree, it's best to first test capacitors. Even a bypass ceramic
could get shorted.

Frank

>
> ----- Original Message -----
> From: Terry Raymond
> To: [hidden email]
> Sent: Thursday, May 25, 2017 2:38 PM
> Subject: C128 problem
>
> Hi,
> My C128 has a problem with blowing the fuse in the power source what could
> cause this?
>
> This C128 is dead, black blank screen, C64/C128 modes won't work, nothing
> She's completely dead.
>
> I was told to check all logic chips, can this be done with a meter or logic
> probe, does this require and voltages on Logic chip pins?
>
> I found jnfo on how to build a simple logic probe, maybe a different post
> later since this
> Has something to do with TTL/CMOS LOGIC OR LS logic, very interesting.
>
> Terry Raymond
>

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