Re: plus4 power supply

On 09/22/2012 05:55 PM, silverdr@wfmh.org.pl wrote:
>
> On 2012-09-22, at 17:29, Gerrit Heitsch wrote:
>
>>>>> BTW, Gerrit - what do you think was the point in providing two +5Vs in the 64? One called +5 and the other CAN+5? Looking at 252312-right, they dropped this idea on the narrow boards. But I am wondering why they introduced it in the first place.
>>>>
>>>> There are 3 reasons I can imagine:
>>>>
>>>> 1) Power, 5V, 2A might have needed a different plug
>>>
>>> I think this DIN should handle 2A w/o problems but In fact I am not sure about the actual specs.
>>
>> Hm... It would be borderline... If the contacts are just a bit worn, you start having a measurable voltage drop on the connection.
>
> But there are two pins allocated for +5. Just by adding second pin to the plug they could have doubled the current there.

You also need 2 pins for GND to make that work properly. Otherwise you 
still have a bottleneck.


> First I simply bent out pin 40 out of the socket and supplied it with +5 from the PWR switch. I noticed (really barely) a degradation to the picture quality but when supplying the same pin with CAN+5, there was virtually no difference. Meaning also a slight (if at all) degradation of the quality. So I decided to do better test and keep the two decoupling capacitors in the loop. So I cut the trace and installed a pinhead like here:
>
> https://dl.dropbox.com/u/58002657/vic_pwr_supply.jpg
>
> and after switching back and forth the supply between +5 and CAN+5 I don't see any difference.
>
> So as the last iteration I removed pin 2 of 7805 and supplied the pad with +5.
>
> https://dl.dropbox.com/u/58002657/whole_can%2B5_replaced.jpg
>
> Again - no noticeable difference at least on the screen. Maybe on a scope someone could notice something but on the screen I see no noticeable difference.
>
> After doing this I tend to believe that it must have been something around 2) or something about utilising the PSU's current capacity better.

Possibly... Maybe they wanted to equalize the load on the 2 outputs of 
the transformer. On the other hand, the 250469-boards put almost all of 
the load on the +5V (about 1.1A) and almost nothing on 9V AC.

But while you're at it... if you feel like it, you could find out what's 
the minimal Vdd (usually +12V, pin 13) for VIC to give you a picture 
with colors. My last attempt was 3 diodes (1N4001) in series, lowering 
the voltage on pin 13 from 12V to about 10V and still everything worked. 
 From my experience with a dead C90, I know that there is a voltage 
where everything still works but the picture loses color. For the 6569R3 
involved that was about 8V.

  Gerrit






       Message was sent through the cbm-hackers mailing list