[Coco] Fwd: Re: Disto Super II controller repair

[Tim Fadden]

For any one following this:

I replaced the  7416 chips.  Upon investigation I see that the head only 
gets the signal to move the head out (low), not in.
This means the 7416 is not going high for the in direction on pin 12. 
The input for this is pin 13 which connects directly to the WD1773. I 
ordered a couple of these.

In the case that this does not fix it, how do I check which chip sends 
the signal to the WD1773?   Which is next in line?  It looks to me like 
U15, the 74HC245 and from there it looks like it goes straight to the 
coco buss.

Please be patient, this my first time trying to trouble shoot this type 
of problem from a schematic!  As a Sun Service rep all I had to do was 
trouble shoot to the fru level, not the chip!  he he....

Also, I have another Super II controller which I tested on the same 
machine, and it works just fine, so I know it is the controller, and not 
the coco.
Any words of wisdom (or not so wise) :-) are appreciated!

Tim

On 5/30/2017 3:10 PM, Bruce W. Calkins wrote:
> The 7406 tolerates higher voltages.  The other specifications are well 
> within the needs for this circuit.  This results in a part that 
> probably will never need replacing.
>
> If I remember correctly, these chips pass the signals that move the 
> drive head among other things.  If the head does not move, the disk 
> does not get formated.
>
> Bruce W.
>
>
>
> On 05/30/2017 01:02 PM, Tim Fadden wrote:
>> Bruce,
>>
>> Ok, I got it stable now, by replacing the ROM socket.
>>
>> I get no head movement when doing a format, so perhaps the 7416 like 
>> you say.  Worth a shot.
>>
>> So, how would one go about checking them, besides just replacing them?
>>
>> And, I was wondering, whats the difference between the 7416, and 
>> 7406. Both are available.
>>
>> Cheers.
>>
>> On 5/29/2017 8:04 PM, Bruce W. Calkins wrote:
>>>
>>>
>>>
>>> -------- Forwarded Message --------
>>> Subject:     Re: [Coco] Disto Super II controller repair
>>> Date:     Mon, 29 May 2017 22:01:24 -0400
>>> From:     Bruce W. Calkins <brucewcalkins at charter.net>
>>> To:     Camillus Blockx <camillus.b.58 at gmail.com>
>>>
>>>
>>>
>>> A common failure on the Tandy controllers was one or both 7416 chips on
>>> the output side.  Removing the chips and socketing a pair of 7406 chips
>>> was the cure.
>>>
>>> I see there are two 7416 chips on the output side of my Super 
>>> Controller
>>> II.  I would suggest starting with checking them.
>>>
>>> Bruce W.
>>>
>>
>
>

-- 
Tim Fadden
"Hey Schmidt, don't forget about the six P's.
Proper Preparation Prevents Piss-Poor Performance!"