[vcf-midatlantic] SASI Hard Drive Controllers

[Mike Loewen]

On Sat, 17 Dec 2016, Dan Roganti via vcf-midatlantic wrote:

> On Sat, Dec 17, 2016 at 6:04 PM, Jonathan Gevaryahu via vcf-midatlantic <
> vcf-midatlantic at lists.vintagecomputerfederation.org> wrote:
>
>> On 12/17/2016 11:03 AM, Dan Roganti via vcf-midatlantic wrote:
>>
>>> On Sat, Dec 17, 2016 at 10:06 AM, william degnan via vcf-midatlantic <
>>> vcf-midatlantic at lists.vintagecomputerfederation.org> wrote:
>>>
>>> Related to my post yesterday, I have a SASI XEBEC 104526 rev 4 that works
>>>> ok when there is a fan blowing on it but overheats after a while.  It
>>>> controls a SASI external hard drive used by a Visual 1050 computer.  OK,
>>>> I
>>>> will look through the electronics and replace failing components and sure
>>>> it up.  Seems like the typical course of action for an XEBEC and other
>>>> (SASI) external controllers.  I am also thinking about the CBM 9090 and
>>>> related 5-10Mb drives. 35 years in, they all seem to be failed or
>>>> failing.
>>>> Similar XEBEC controllers for things like IBM PC's seem to have fared
>>>> better.  Why?  Or just a coincidence?  Is there a common component that
>>>> fails more often in SASI controllers but not IDE and others of the era?
>>>>
>>>> I know the history of SASI/SCSI and I have some XEBEC docs.    I can
>>>> research further on my own, but maybe someone who actually supported
>>>> these
>>>> back when they were new has some casual knowledge to pass along.  How
>>>> reliable were these when they were new/current?
>>>>
>>>> Bill
>>>>
>>>>
>>> ?I don't have any repair history of that board, I think that's a long shot
>>> Unless you find someone who worked at XEBEC, they would have a more
>>> comprehensive view of failures.
>>> And most if not all of those components are well beyond their mtbf rating
>>> already.
>>> So that basically means, anything can go wrong.
>>> But the basic repair steps for something like this include several options
>>> One of which is using a ol' tried and true method of finding the hot
>>> component, your finger :)
>>> That's if the slot has room for you to get in there.
>>> There's other options such as using a temperature probe[thermocouple]
>>> adapter for your DMM.
>>> So you can measure the heat from each component.
>>> Also, for these tricky problems it helps to have a thermal imager -
>>> they're
>>> getting cheaper every year.
>>> Then you can pinpoint the source of the heat, but first turn off the Fan
>>> :)
>>> Dan
>>> .
>>>
>>> Can't you use a FLIR or similar thermal camera to figure out which IC or
>> capacitor has a partial/internal short, and replace just that one?
>> Keep in mind that some ICs normally get hotter than others, though.
>>
>>
> ?that was in my 3rd option

    Don't neglect the simple resistor as the culprit in your 
troubleshooting.  Back in the day, I used the freeze spray/heat gun method 
to track down a problem in the floppy controller of my TRS-80 Model 4 to a 
resistor whose value changed just enough when warm to make the controller 
fail.


Mike Loewen				mloewen at cpumagic.scol.pa.us
Old Technology				http://q7.neurotica.com/Oldtech/