VT101 8085 CPU Fault

[Robert Jarratt]

> -----Original Message-----
> From: cctalk [mailto:cctalk-bounces at classiccmp.org] On Behalf Of Matt
Burke
> Sent: 22 February 2015 13:56
> To: cctalk at classiccmp.org
> Subject: Re: VT101 8085 CPU Fault
> 
> On 21/02/2015 18:59, Robert Jarratt wrote:
> > So what sort of value is reasonable for leakage?
> 
> You need to look at the datasheet for each capacitor to find out what the
> maximum leakage should be. Here is an example taken from the Panasonic M
> Series datasheet:
> 
> DC Leakage Current: I <= 0.01CV or 3uA after 2 minutes (whichever is
> greater)
> 
> So if C321 on the monitor board was a Panasonic M series then the leakage
> would be:
> 
> I = 0.01 x 1000uF x 16V = 160uA
> 
> You need to connect a DMM with mA (or better uA) range in series with the
> bench supply and capacitor so you can check that the leakage falls below
this
> value. You may find that it takes a while to reach this value if the
capacitor has
> not been reformed recently.
> 
> Once you've done a few of these you may not need to look at the datasheet
> every time as you will get to know what reasonable values are for a given
> capacitance and voltage.
> 
> Matt


I did pretty much what you say last night. All the caps settled down to a
leakage of the order of 10-20uA after no more than a minute on their maximum
voltage. Although my bench PSU does not go to the 50V needed for some of the
caps. Was considering putting the board back in after having done some light
reforming on them (ie not for more than a couple of minutes each), in case
they just needed reforming.

Regards

Rob