VT101 8085 CPU Fault
js at cimmeri.com
js at cimmeri.com
Sat Feb 21 12:42:42 CST 2015
On 2/21/2015 1:33 PM, Robert Jarratt wrote:
> I have been desoldering and checking
> all the electrolytics. I have set each
> one up on my bench PSU with the
> current limiter set, and taking them
> up to their rated voltage, or as near
> as I could because some are rated 50V
> and my bench PSU only reaches 30V.
Then you need a better bench PSU or a
dual supply that allows you to gang them
in series (like mine does, 2x30 -> 60V).
> None of them seemed to show any
> leakage, but my bench PSU will not
> display currents below 10mA
That's not good enough either. 10Ma
would be far too much leakage.
> I am not sure if that is enough to
> show leakage that matters. I also
> tested their capacitance values, a few
> are well above nominal value, but
> within the tolerance shown on the
> printset. The worst one is +41% when
> the range is +50-10%.
Why do you consider +41% to be "worst"?
Sounds better to me.
> I started checking some of the
> tantalum capacitors. They all looked
> fine, but I don't know what a sensible
> ESR value is for these. One of them
> (C315) is rated 1uF 35V and has an ESR
> of 3.4. Is that high for a tantalum?
> One respondent asked for a picture,
> the printset is here,
> http://manx.classiccmp.org/details.php/1,5422
> and the relevant drawing is on page 58.
That was me. Do you have a photo of the
actual board you're working on?
As far as the non-electrolytics, mainly
start by just making sure none of them
are shorted or open.
- J.
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