Re: Pet64 DOA

Ok this morning I printed out the schematic and theory of operation  
for the C64.

The theory of operation states that the reset signal is originally  
produced at pin 9 of the 556 time (MC3456p in my case). The output is  
active high. I have tested this pin with my probe, and it does indeed  
switch from low to high on power-up. The theory of operation then says  
that this signal is sent to pin 13 of a 7406 hex inverter (U8) and the  
output from the 7406 is active low from pin 12...this is the reset  
signal.

However, on my machine pin 9 of the 556 is tied to pin 13 (on the same  
556) with some wire, and I have tested the continuity from pin 9 of  
the 556 to pin 13 of the 7604, and I can't see any physical connection  
between these pins which in contrary to the schematic and the theory  
manual. Maybe I'll pull the board out and have a look at the bottom  
side for any damage or cut traces.

I probed pins 12 and 13 of the 7406 and pin 12 is always low and pin  
13 is always high.

So I'm a little confused...this doesn't seem right. Maybe I can I  
briefly apply 5v to pin 12 of the 7604 to see what happens?

Maybe I have the wrong schematic, but I don't think so. I'll look for  
others anyway.




On Dec 10, 2010, at 12:43 AM, MikeS wrote:

> The supply voltages to the ICs are all correct?
>
> Reset line is being released?
>
>
> ----- Original Message ----- From: "Philip Lord" <random6000@mac.com>
> To: <cbm-hackers@musoftware.de>
> Sent: Thursday, December 09, 2010 3:23 AM
> Subject: Re: Pet64 DOA
>
>
>> Well, it seems like the power might be ok after all, so I broke out  
>> my  logic probe...it's a cheap one but has helped me fix many  
>> simple  issues over the years.
>> The first think I noticed after probing around is that I'm not  
>> getting  any pulsing (or at least that what the probe indicates),  
>> lines are  either high, or low, or nothing, but there doesn't seem  
>> to be any  pulsing at all!
>> So I guess I should look at the timing circuit or Xtal? Anywhere  
>> else?  Not sure how to test is a Xtal is working as I don't think  
>> my probe  can do that.
>> Cheers
>> Phil
>> On Dec 9, 2010, at 2:10 PM, Philip Lord wrote:
>>> Great...so then maybe my power voltages are all good? Should I  
>>> find  some test point on the C64 motherboard and get some voltages  
>>> there?  Any idea what I should check next?
>>>
>>> Re-PET board. Ethan has been working very hard, and he believes  
>>> he  has fixed both boards now (but can not test loading as his C2N  
>>> data  cassette deck is in need of a new drive belt). Last I heard   
>>> everything is almost packed up and ready to ship. It would be  
>>> great  to get the boards back before years end, as I have been  
>>> building a  number of add-ons in anticipation for their arrival  
>>> and I'm excited  to try everything out.
>>> I have built one of Nicolas Welte's Ram/Rom boards which will   
>>> hopefully take my ram to 32k and allow me to use various basics  
>>> (V1  through V4) and not have to worry about failing RAM in the  
>>> future. I  have also built a number of adaptor boards to replace  
>>> the video ram  and character ROM. Finally I got myself a C2N232 as  
>>> I don't know how  reliable the original cassette drive is. I'm  
>>> hoping to 'fail proof'  this machine for at least another 30  
>>> years ;-)
>>>
>>>
>>>
>>>
>>> On Dec 9, 2010, at 1:44 PM, MikeS wrote:
>>>
>>>> 5V DC and 9V AC - sounds OK.
>>>>
>>>> Did you finally get your PET boards back and working?
>>>>
>>>> m
>>>>
>>>> ----- Original Message ----- From: "Philip Lord" <random6000@mac.com 
>>>> >
>>>> To: <cbm-hackers@musoftware.de>
>>>> Sent: Wednesday, December 08, 2010 10:41 PM
>>>> Subject: Re: Pet64 DOA
>>>>
>>>>
>>>>> 8.91 vac
>>>>> On Dec 9, 2010, at 12:31 PM, MikeS wrote:
>>>>>> Hi Philip!
>>>>>>
>>>>>> What AC voltage do you get between the two white wires?
>>>>>>
>>>>>> mike
>>>>>>
>>>>>> ----- Original Message ----- From: "Philip Lord" <random6000@mac.com 
>>>>>>  >
>>>>>> To: <cbm-hackers@musoftware.de>
>>>>>> Sent: Wednesday, December 08, 2010 10:07 PM
>>>>>> Subject: Re: Pet64 DOA
>>>>>>
>>>>>>
>>>>>>> Sorry maybe I should have tested the some lines using AC not DC.
>>>>>>> So here again is what I believe I have (suing the black line  
>>>>>>> as  GND):
>>>>>>> White: - 5.8 vac
>>>>>>> (KEY)
>>>>>>> White - 0.5 vac
>>>>>>> Black (I'm guessing this is ground)
>>>>>>> Red - 4.98 vdc
>>>>>>> Of course I could just be confused as I've never owned a C64   
>>>>>>> before.
>>>>>>> Looking at schematics seems maybe the two white lines could/  
>>>>>>> should  be  9vac, and maybe the red line should be 5 vdc???
>>>>>>> Phil
>>>>>>> On Dec 9, 2010, at 11:16 AM, Philip Lord wrote:
>>>>>>>> I just got myself a PET64 from Yahoo Auction Japan. Quite a   
>>>>>>>> rare   machine I hear, so I'm not sure how one ended up in   
>>>>>>>> Japan. I got  if  for a decent price as I don't think the   
>>>>>>>> Japanese knew exactly  what  it was.
>>>>>>>>
>>>>>>>> Anyway, It arrived the other day, after a quick internal    
>>>>>>>> inspection,  I powered it on. I can hear the transformer    
>>>>>>>> buzzing(!), but no  action at all on the screen at all, and  
>>>>>>>> it   doesn't seem like the  chips are getting warm at all  
>>>>>>>> Maybe need  to  leave it on a little  longer to make sure,  
>>>>>>>> but I didn't  want to do  that incase bad  voltages kill  
>>>>>>>> anything more).
>>>>>>>>
>>>>>>>> There are 4 wires leading from the small PCB which is  
>>>>>>>> attached  to   the transformer to the C64 motherboard, and I  
>>>>>>>> have  measured the   voltage from the black wire (GND?) to  
>>>>>>>> the 3  others. Here are the   reading i get:
>>>>>>>>
>>>>>>>> White: - 100mv
>>>>>>>> (KEY)
>>>>>>>> White - 100mv
>>>>>>>> Black (I'm guessing this is ground)
>>>>>>>> Red - 4.98v
>>>>>>>>
>>>>>>>> That's as far as I have gotten. Next I will remove the    
>>>>>>>> motherboard  and see where exactly these 4 wires go.
>>>>>>>> Anyway, I was just wondering if anyone had any insights or   
>>>>>>>> thoughts.
>>>>>>>>
>>>>>>>> Cheers
>>>>>>>> Phil
>>>>>>>   Message was sent through the cbm-hackers mailing list
>>>>>>
>>>>>>   Message was sent through the cbm-hackers mailing list
>>>>>    Message was sent through the cbm-hackers mailing list
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>>>
>>>
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