11/45, sick or not?

Mike Cesari mcesari at comcast.net
Tue Jul 5 22:31:11 CDT 2005


On Jul 5, 2005, at 6:45 PM, Jay West wrote:

> Joe wrote...
>
>>  Are you sure that the lights aren't blinking too fast to see?  
>> Perhaps you
>> can hang a logic probe (with a pulse extender) on one of the  
>> lights to be
>> sure.
>>
>
> I'll try that tomorrow... but I wouldn't think that is what is  
> happening. Also, pardon my lack of knowledge, but... shouldn't I be  
> seeing the .2v ripple as an AC component (ie. a sine wave)? It's a  
> very clear perfect sawtooth. And it's exactly the same on all the  
> 5V regulators, which strikes me as odd.
>
> Jay
>

The sawtooth is correct for h744's. 0.2v is a bit much, but shouldn't  
be a show-stopper. The 11/70 maint. manual has a
decent description of the h744 on pages 4-59 thru 4-62 (EK-11070- 
MM-002_May79.pdf on bitsavers). It says the voltage should
range from 4.95v - 5.05v. (The description in the 11/45 manual isn't  
as good.)

Also check for high frequency spikes at the valleys of the sawtooth,  
for example:

5v_     /\  /\   ...     If these are more than 2 volts (go below  
3v), you will have "issues".
        /  \/  \/         Welcome to the wonderful world of aged DEC  
switching supplies =:O
            |   |
3v_        |   |

Ascii art, feh. Put up some pics of the `scope display. :-)

Mike




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