Re: 6561-101

Re: 6561-101Hi,

You are right. I have not noticed it in the schematic...
This must have been the reason!
Thanks
Istvan

From: Julian Perry 
Sent: Thursday, November 17, 2016 11:11 PM
To: cbm-hackers 
Subject: Re: 6561-101

The same 7406 also drives RESET from the 555 timer, and inverts θ0 (clock) from the VIC. It's likely it was holding reset down, or otherwise messing with the clock.

As to why removing the 6522's triggered a change, I'd guess that this was due to some weird interaction between inputs arising from failed silicon on the die of the 7406.
Always nice to hear of another VIC brought alive!  The numbers of working VICs continue to shrink alarmingly.

Julian


> Hi,

> I have managed to repair my VIC20. It was the SN7406 next to the 6522 ICs.
> When I have removed the 6522s the computer came alive but with garbage
> characters on the screen. When the 6522s were in place there was just black
> screen.
> After replacing the SN7406N everything was ok, the 6522s work fine. How
> could this 7406 cause this problem when it is not connected to the databus
> only to the 6522s?

> Istvan

> -----Original Message----- 
> From: Didier Derny
> Sent: Wednesday, October 26, 2016 1:57 PM
> To: cbm-hackers@musoftware.de
> Subject: Re: 6561-101

> Hi

> to repair your vic20 you can use this product:

> http://vic-20.de/x1541/hardware/petram.html

> it replaces ram and/or rom...

> it helped me to fix a old cbm 8032...


> it is clear that if the VIC is not correctly initialized you probably
> get a black screen.




> On 26/10/2016 10:33, Hegedűs István wrote:
>> The problem is that this is my first ever VIC20 so I have no cartridges... 
>> The idea is however good.
>> Thanks
>> Hege


>> -----Original Message----- From: Clockmeister
>> Sent: Wednesday, October 26, 2016 3:00 AM
>> To: cbm-hackers@musoftware.de
>> Subject: Re: 6561-101



>> On 26/10/2016 4:38 AM, Hegedűs István wrote:
>>> Hi,

>>> It has black screen of course. I know that the Kernal ROM or VIC used to 
>>> be the guilty ones. I have burnt a 27c128 with Kernal but still have to 
>>> build an adapter so I cannot 100% rule out Kernal issue. The guy who sold 
>>> it said that the 6502 is also sick (he has tried the CPU in an 1541), 
>>> though with oscilloscope I have seen e.g. proper phi2 signal coming out. 
>>> I have bought some Rockwell 6502s to replace it. Anyway even if it turns 
>>> out that VIC is good it is better to have a spare IC.
>>> I should hook up my logic analyzer to it but so far I had no time (or I 
>>> was just too lazy).



>> Whilst mask ROM (and RAM for that matter) failures are common on vintage
>> equipment, the last two VIC-20's with a black screen that I repaired had
>> a bad 6561-101.
>> In my case both were easy to diagnose by simply plugging in a cartridge
>> or blind loading a game. On both occasions the game you could hear the
>> game playing even though there was a black screen.





>>       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 


>        Message was sent through the cbm-hackers mailing list




-- 
Best regards,
Julian                            mailto:jp@digitaltapestries.com Message was sent through the cbm-hackers mailing list 


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