[Coco] Weird CoCo3 problem...

[Bob Devries]

Brian,

as far as I know all 512k upgrades required those caps to be clipped. I'd be 
worried about that problem with R22 also. You should check to see if R22 is 
in fact still a resistor, and not an open circuit. As I recall, it should be 
a low ohms value.

Regards, Bob Devries
Goulburn, NSW, Australia
(soon to be in Las Pinas City again)

--
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: "Brian Blake" <random_rodder at yahoo.com>
To: "CoCoList for Color Computer Enthusiasts" <coco at maltedmedia.com>
Sent: Sunday, January 03, 2010 5:06 PM
Subject: Re: [Coco] Weird CoCo3 problem...


> Hi Bob,
>
> Do those caps both get clipped with any 512k upgrade? C66 has definitely 
> been re-soldered. Looks like the prev owner tried, but, failed to 
> re-solder C65 - it is not soldered together. Looking at his soldering 
> jobs, I'd have to say that he should never be allowed to even look at a 
> soldering iron - I've done quite a bit of cleanup of solder splats and the 
> solder on the wires to R22 are scary. I tried to boot the CoCo with the 
> alligator clips detached, and was greeted with a green screen with no 
> text. Tried again and got the same thing. Reconnecting the clips allowed 
> it to boot.
>
> At any rate, I clipped off the 6809 today. Forgot my solder sucker is at 
> work, so, I've got a CoCo3 mobo with no CPU right now. Just need to 
> remember to be patient and not damage the soldering pads with too much 
> heat....
>
>
>
> ________________________________
> From: Bob Devries <devries.bob at gmail.com>
> To: CoCoList for Color Computer Enthusiasts <coco at maltedmedia.com>
> Sent: Sun, January 3, 2010 12:23:29 AM
> Subject: Re: [Coco] Weird CoCo3 problem...
>
> Brian,
>
> after having checked out the schematic of the NTSC Coco3, I realised that 
> the capacitors C65 and C66 should be removed if a 512k expansion board is 
> installed. I believe also that R23 was affected, but if I remember 
> correctly, it was only short circuited with a 1MB expansion (from Disto). 
> These components are in the /CAS and /RAS part of the circuitry near the 
> GIME.
>
> --
> 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: "Brian Blake" <random_rodder at yahoo.com>
> To: "CoCoList for Color Computer Enthusiasts" <coco at maltedmedia.com>
> Sent: Saturday, January 02, 2010 6:05 AM
> Subject: [Coco] Weird CoCo3 problem...
>
>
>>
>>
>> All of these new developments on the CoCo front finally lit the fire 
>> under my arse to set up real hardware again. Besides my repack project, I 
>> have 3 other CoCo3's, two with 512k upgrades (one C9 and one PBJ) and one 
>> 128k. The one with the C9 upgrade works fine - can load and play 
>> Sockmaster's Donkey Kong.
>>
>> The one with the PBJ upgrade, not so... At boot, it comes up as it should 
>> with the proper display. However, any floppy commands are met with no 
>> response from the floppy drive (with an FD-502 controller) at all. Almost 
>> like the drive is off. The drive responds as it should in the other two 
>> machines. Upon removing the top case and k/b, I saw two wires, each had 
>> been soldered to opposite sides of R23. Now, under the keyboard, is 
>> another wire with alligator clips on each end, and the clips are holding 
>> on to the bare end of the wires soldered to R23, effectively bypassing 
>> the resistor. I'm looking for the PBJ instructions, pretty sure I have 
>> them, to find out if this is called for. I can also see where C65 & C66 
>> have been cut and re-soldered. I have reseated the GIME and the PBJ 
>> memory chips, and cleaned the 40 pin connector.
>>
>> Any other suggestions? My 100MHz o'scope bit the dust so I don't have 
>> that tool any more (anybody have a CRT for a Leader 3 channel 100MHz 
>> scope??)
>>
>>
>> Thanks,
>>
>> Brian
>>
>>
>>
>>
>> --
>> Coco mailing list
>> Coco at maltedmedia.com
>> http://five.pairlist.net/mailman/listinfo/coco
>
>
> --
> Coco mailing list
> Coco at maltedmedia.com
> http://five.pairlist.net/mailman/listinfo/coco
>
>
>
>
>
> --
> Coco mailing list
> Coco at maltedmedia.com
> http://five.pairlist.net/mailman/listinfo/coco