[Coco] Weird CoCo3 problem - AAAARRRGGGGGHHHHH!!!!

[Bob Devries]

Bruce,
Brian has already mentioned that the controller works in another coco3, so 
the components on the controller are not suspect IMHO.

--
Besides a mathematical inclination, an exceptionally good mastery of one's 
native tongue is the most vital asset of a competent programmer.

Edsger W.Dijkstra, 18 June 1975

----- Original Message ----- 
From: "Bruce W. Calkins" <brucewcalkins at charter.net>
To: "CoCoList for Color Computer Enthusiasts" <coco at maltedmedia.com>
Sent: Monday, January 04, 2010 9:08 AM
Subject: Re: [Coco] Weird CoCo3 problem - AAAARRRGGGGGHHHHH!!!!


> IIRC; there are two 74LS16s on the output side of the controller. These 
> are slightly underrated and often fail.  I have removed them, replaced 
> them with sockets and installed 7416s which restored functionality.
>
>
>
> Bruce W.
>
> =========================================
>
> ----- Original Message ----- 
> From: "Brian Blake" <random_rodder at yahoo.com>
> To: "CoCoList for Color Computer Enthusiasts" <coco at maltedmedia.com>
> Sent: Sunday, January 03, 2010 4:35 PM
> Subject: Re: [Coco] Weird CoCo3 problem - AAAARRRGGGGGHHHHH!!!!
>
>
>> The latest;
>>
>> Upon further testing, R22 was not doing anything. The solder pad on the 
>> bottom of the mobo was broke, an the leg on the end that's supposed to 
>> connect to C65 had been lifted. I took R22 completely out and replaced it 
>> with a new 120-ohm resistor. Then I took a short piece (3/16 - 1/4") of 
>> speaker wire and soldered it to the leg of R22 that is supposed to go to 
>> pin 4 of the GIME, scraped away some green stuff and soldered the other 
>> end directly to the trace. Continuity restored. Continuity from R23 was 
>> fine. Cleaned up the solder pads from where I clipped out the 6809, 
>> soldered in the socket, installed the 6309 and put everything back 
>> together. Turn her on and was greeted with the 'Extended Color 
>> Basic....yada, yada' greeting, okay that worked. Tried Tetris, S/S Pak 
>> and O-90, all worked as expected. Still have the same problem with the 
>> FD-502; POKE &HFF40,1 does not turn on the drive light, and any disk 
>> commands end up with an I/O? error with no activity
>> being present on the drives when the commands are issued... 
>> AAAARRRGGGGGHHHHH!!!!
>>
>> I went to R/S today only to find out they no longer carry a logic probe, 
>> so I'm stuck with using my DMM for now. When issuing a POKE &HFF40,1 in a 
>> loop, IC9 pin 6 is 'HI' on the DMM in logic mode, but, in frequency mode 
>> it shows up as a 192.5-kHz signal. Pin 36 of the 40 pin connector shows 
>> the same results. Other than evidently ruining a perfectly good 6809, so 
>> far the only thing I've accomplished is completing a 6309 swap on a CoCo3 
>> with 'floppy phobia'... So, I'm still open for suggestions. Tomorrow I'll 
>> be bringing home my 50-MHz scope so I'll at least be able to look at 
>> waveforms. At this point,based on my limited knowledge and materials I'm 
>> looking at, I'm leaning towards replacing IC9 to see if that helps, but, 
>> I'd rather not start chip swapping just for the heck of it, so PLEASE, if 
>> you guys who are far more knowledgeable than I have any suggestions, I'm 
>> listening!!!
>>
>>
>> Thanks,
>>
>> Brian
>>
>>
>>
>>
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>
>
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