-----Original Message-----
From: cctalk [mailto:cctalk-bounces at
classiccmp.org] On Behalf Of
js at
cimmeri.com
Sent: 21 February 2015 18:43
To: General at
classiccmp.org; Discussion at classiccmp.org:On-Topic and Off-
Topic Posts
Subject: Re: VT101 8085 CPU Fault
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).
Longer term I will have to get one, but for now that is all I have. I do
have a variac and a rectifier, so I could get it to 50V that way.
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.
So what sort of value is reasonable for 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.
By "worst" I mean the one that was furthest from its nominal value.
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?
I have posted a picture of it here:
http://1drv.ms/1Lo1hWB
As far as the non-electrolytics, mainly
start by just making sure none of them
are shorted or open.
- J.