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Hi David

I had wondered about upgrading my 7854 with newer RAM and ROM boards and was even considering laying out new PCB's. I havn't looked at pricing for a small run of PCB's but it is probably cheaper than buying new Tektronix boards.

I don't think it would be worth trying to modify an old RAM card for battery backup as the standby current is probably too high. Will look into it at a later date.

Chris

--- In TekScopes@..., "David C. Partridge" wrote:

David,

Do you have the schematics of this later memory board? I think it would be a great modification to change the earlier board to do this too.


Regards,
David Partridge
-----Original Message-----
From: TekScopes@... [mailto:TekScopes@...] On Behalf Of David
Sent: 21 January 2013 16:35
To: TekScopes@...
Subject: Re: [TekScopes] Re: 7854 RAM magic

I believe the behavior you are seeing is normal.

I have the most recent 7854 hardware version which has a lithium backup battery mounted on the memory board. On the back of the mainframe where the connections for external memory backup power used to be, there is a toggle switch which selects between self test and memory backup.

In self test mode, the memory is cleared every time the mainframe is powered up and the self test is run.

In memory backup mode, the self test is skipped and the mainframe starts in stored mode. "SELF TEST" on the ID screen is replaced with "NV MEMORY".




On Mon, 21 Jan 2013 15:20:24 -0000, "bogroca"
wrote:

Hi Herbert,

I assumed that myself.

The question that bothers me, is that about what is the NORMAL behaviour when power-up with the battery back-up connected?

The manuals, both the op and service, say on page 1-7 and 1-3 respectively:

"Power-up Conditions
When the 7854 is turned on (without the memory back-up applied)..."

Bet never gets back to the topic, WITH the memory back-up applied.

Any thoughts?


Best regards,

Bogdan

--- In TekScopes@..., "Herbert" wrote:

Hi Bogdan,

it is normal for the HM62256B to keep the data down to approx. 1V.
I think what zou see is, that the system does not recognnize the power off phase .

Herbert


--- In TekScopes@..., "bogroca" wrote:

Hi all,

After replacing the ROMs (document to come soon), I got on to the RAM.

Replaced all 91L24 chips with 2x HM62256B (that's all I had at hand), thinking to first try out the simple SRAM and then, if all OK, to move over to NVSRAM like DS1230.

First boot with the new chips went fine, but then, to my surprise, from the second boot on, it bypassed the self-check routines, booting (seem correctly) directly into the scope mode. Quickly digitized a wave and display it. All good. Powered off and then on again...

...It booted directly in the "stored" mode with the right wave displayed.

I can assure you that the first impulse was to check if the battery backup is present. The second was to see if, by mistake, I did not inserted the NVRAM chips instead. None of this was true. It must be some energy stored in the caps. Tested some more and got to fully discharge in about 3-4 minutes, when it boots with the self-check.

One question, before proceeding further: is it normal to bypass the self-check if the contents of the RAM is still present, like when the backup battery is present? I find this a little weird.

Sorry for the long post and thank you inadvance!

Bogdan

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