[Coco] Weird CoCo3 problem...

[Brian Blake]

Hi Bob,

Clipping those caps is what my memory was telling me as well, but, I trust your memory better than mine, lol. 

R22 is supposed to be a 120-ohm resistor and it check out to be 118.6 - within the 5% tolerance.





________________________________
From: Bob Devries <devries.bob at gmail.com>
To: CoCoList for Color Computer Enthusiasts <coco at maltedmedia.com>
Sent: Sun, January 3, 2010 1:30:02 AM
Subject: Re: [Coco] Weird CoCo3 problem...

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
>> 
>> 
>> 
>> 
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