Q-Bus Memory Diagnostics and Repair

Jerry Weiss jsw at ieee.org
Sun Sep 25 20:34:51 CDT 2016

On Sep 9, 2016, at 8:17 PM, Jerry Weiss <jsw at ieee.org> wrote:
> On Sep 9, 2016, at 6:11 PM, Noel Chiappa <jnc at mercury.lcs.mit.edu> wrote:
>>> If your CPU is an 11/73 (which can directly 'access' [hate that verbism
>>> :-] all of memory from ODT, unlike the 11/23 which is restricted to the
>>> bottom 256KB), try playing around with a failing location, and its
>>> alternative, directly, and see if a store of random data into one can be
>>> read back directly from the other
>> Note: The 11/'73' CPU powers up with the cache enabled, even for ODT!
>> So if you write xxx into some location, if you then read it back, you will get
>> the correct data even if the memory location is busted - the CPU is getting
>> the (correct) data from the cache. To have your 'memory' reads and writes
>> actually go to the memory, you need to turn off the cache:
>> 17777746/ 02000 
>> Note that starting the machine does an INIT, which will again enable the
>> cache.
> That’s a very good piece of information, I hadn’t considered that.  I have 11/73. 
> I’ve checked the memory with ODT and can confirm the stuck bit.

Finally got back to this.  First clipped VCC on the suspect
and confirmed that the bank and address range was the same as the original error.

So finally pulled out the soldering iron and replaced as chip.   Back to memory test
and all is now good.
     R VMJA??
        11/83 CACHE AVAILABLE

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I board fixed, one to go.  Thanks for the support.


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