DEC KA650 VAX memory troubleshooting

Joseph Zatarski joezatarski at
Sun Nov 24 09:35:40 CST 2019

I used an HP 16700A, which you can see in the video I linked some time back:

On 11/24/19 8:27 AM, W2HX wrote:
> Wow. Very nicely done! Which logic analyzer did you use to capture those displays?
> 73 Eugene W2HX
> ________________________________________
> From: cctalk <cctalk-bounces at> on behalf of Joseph Zatarski via cctalk <cctalk at>
> Sent: Sunday, November 24, 2019 1:28 AM
> To: General Discussion: On-Topic Posts
> Subject: Re: DEC KA650 VAX memory troubleshooting
> Well, I finally got around to posting this on the CHWiki, in case
> anybody was curious about this.
> On 6/17/19 7:56 PM, Joe Zatarski wrote:
>> OK, so where should a thing like this go:
>> Anybody got a decent place to upload that? it's my notes on the
>> MS650-AA, and more generally the KA650 CMCTL memory subsystem.
>> Includes my theory of operation of the CMCTL, the organization of
>> memory, the ECC equations (kinda, the info is there to derive them),
>> explanations of the signals on the memory bus, and most importantly, a
>> list of which bits and RAM regions correspond to the 312 DRAMs on the board.
>> On Sat, Jun 15, 2019 at 8:33 PM Joe Zatarski <joezatarski at
>> <mailto:joezatarski at>> wrote:
>>   >
>>   > Hey Everyone,
>>   >
>>   > I just thought I'd share a video of how I'm going about
>> troubleshooting the bad DRAMs on my MS650 memory board.
>>   >
>>   >
>>   >
>>   > I apologize for the shaky-cam, I don't have a tripod, and I needed to
>> do a lot of panning anyway.
>>   >
>>   > I will be sharing my notes on the MS650 once I have a chance to write
>> them up properly as well. I wasn't able to find a printset for the RAM
>> card itself, so I assume one doesn't exist in digital form yet. I have
>> documented what bit and memory range each DRAM on the card corresponds
>> to, which may help someone troubleshooting in the future
>>   >
>>   > Regards,
>>   > Joe Zatarski

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