RE: Will pay good money for NON working PET 2001 motherboard.

Phil, 

Ah... and if you DONT have the high resistance measurement then the
transistor is Bad. Since you are checking in circuit something in the
circuit could be shorted so it is best to pull the transistor in question
out of the circuit and test again. 

-----Original Message-----
From: Scott [mailto:rylos@charter.net] 
Sent: Sunday, November 08, 2009 09:58
To: 'cbm-hackers@musoftware.de'
Subject: RE: Will pay good money for NON working PET 2001 motherboard.

Phil, 

Phil wrote:
I'm also wondering how exactly would you test for a short in a  
transistor??? Is that something that can be done in circuit  with a  
multimeter?

Yes...

Look on the internet to see which pin on your type of transistor (transistor
case style) is the base. Then, using your multimeter on resistance or Ohm's,
go between base and the other two leads noting the results. Swap your leads
and measure from base to the other two leads again noting the results. For a
"electrically" good transistor you should have got the following results. 

1st or 2nd test
Short - 0 ohms
Short - 0 ohms

2nd or 1st test
Short - 0 ohms
Open - High resistance. 

Between the Base and the emitter of the transistor it should check like a
Diode. Letting current flow one way but not the other. But it still may be
breaking down under voltage. Checking from Base to collector should be
shorted or have very low resistance both ways.

Hope this helps. 


-----Original Message-----
From: owner-cbm-hackers@musoftware.de
[mailto:owner-cbm-hackers@musoftware.de] On Behalf Of Philip Lord
Sent: Sunday, November 08, 2009 07:54
To: cbm-hackers@musoftware.de
Subject: Re: Will pay good money for NON working PET 2001 motherboard.

Hi William,
Thanks for he reply.
For my own education, I was wondering why you feel the the transistors  
are the issue?
I'm also wondering how exactly would you test for a short in a  
transistor??? Is that something that can be done in circuit  with a  
multimeter?

I'll take your advice on dismantling the keyboard and cleaning with  
alcohol. I'll need to be especially careful as this keyboard is  
actually a Japanese variant with Japanese characters also printed on  
the keys.

Thanks again
Phil


On Nov 8, 2009, at 2:10 PM, William Levak wrote:

> On Sun, 8 Nov 2009, Philip Lord wrote:
>
>>>> First thing I noticed was that there were many keys not working or
>>>> working sporadically, however I was still able to quickly write a
>>>> 'hello world' program to confirm that the basic was function
>>>> correctly. All seemed good until I tried to load a tape. After  
>>>> typing
>>>> 'LOAD' and pressing return the computer would freeze. I would not  
>>>> get
>>>> the 'press play now' message, and the tape drive would no longer
>>>> function. Turning the machine off and on again brought the machine
>>>> back to life, and the tape drive was able to move again through FF,
>>>> REW and PLAY buttons. Typing LOAD or SAVE would lock everything up
>>>> again.
>
> Sounds like a short in the cassette moter switching transistors, Q1  
> - Q6.
>
> Problems with the keys is normal for these computers.  First thing  
> to try is to take apart the keyboard and clean the contacts with  
> alcohol.
>
>
>      Message was sent through the cbm-hackers mailing list


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