Author Topic: Trying to find old 8k sram chips for HP-75c calculator pod  (Read 3589 times)

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Online oPossum

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Re: Trying to find old 8k sram chips for HP-75c calculator pod
« Reply #25 on: June 09, 2019, 07:33:48 am »
Is 15 "faster" than 12 or 10 ?

Smaller numbers are faster. Less time between stable address and valid data.
 
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Online RichardMTopic starter

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Re: Trying to find old 8k sram chips for HP-75c calculator pod
« Reply #26 on: June 09, 2019, 09:01:44 am »
I will definitely use them, thanks. Can I PM you my details ?
Cheers
 

Offline Kjelt

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Re: Trying to find old 8k sram chips for HP-75c calculator pod
« Reply #27 on: July 04, 2019, 03:27:32 pm »
You have a pm, need your address for shipping.
 

Offline james_s

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Re: Trying to find old 8k sram chips for HP-75c calculator pod
« Reply #28 on: July 04, 2019, 04:40:32 pm »
8k*8 SRAM chips are common as muck. You can buy them from Digikey or other reputable sellers for a few dollars each. It will cost more to ship an old board than it costs to just buy brand new known working chips.
 

Offline Kjelt

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Re: Trying to find old 8k sram chips for HP-75c calculator pod
« Reply #29 on: July 04, 2019, 04:51:24 pm »
Besides these are not just srams they are ultra low power versions with uktra low leakage current.
 

Offline james_s

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Re: Trying to find old 8k sram chips for HP-75c calculator pod
« Reply #30 on: July 04, 2019, 07:13:38 pm »
What was considered ultra low leakage current when the HP-75 was made is nothing special today.

https://www.digikey.com/product-detail/en/alliance-memory-inc/AS6C6264-55SCN/1450-1037-ND/4234596

1uA typical standby current, 2.7-5.5V supply range, 55ns access time, 28 pin SOP, current production part and only $2.13 each in single quantity. Am I missing something? Because this looks like a fully compatible and superior part.
 
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Online oPossum

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Re: Trying to find old 8k sram chips for HP-75c calculator pod
« Reply #31 on: July 04, 2019, 11:19:00 pm »
That looks like a nice universal replacement for 6264 RAMs. Fast, low power, and DIP/SOP/TSOP packages.
 

Offline chickenHeadKnob

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Re: Trying to find old 8k sram chips for HP-75c calculator pod
« Reply #32 on: July 04, 2019, 11:37:15 pm »
As Kjelt tried to caution RichardM I would also doubt that the RAMs are faulty. I would not eagerly replace them first as they do not just go bad on their own. Only two things commonly kill them, static discharge and an out of range power supply. In either of those two cases it is more likely for a static discharge to go through what ever is connected to the keyboard, likewise a power rail disruption or reversal could easily kill everything not just the RAM.

You can measure the resistance of the cruft on the PCB with a multimeter if it is conductive enough.
 

Offline james_s

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Re: Trying to find old 8k sram chips for HP-75c calculator pod
« Reply #33 on: July 05, 2019, 12:59:53 am »
I thought he wanted additional chips to fill blank spots on the board, not to replace suspected faulty parts?

I've seen a lot of faulty SRAM chips on old arcade games but those are mostly 2114's.
 

Offline chickenHeadKnob

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Re: Trying to find old 8k sram chips for HP-75c calculator pod
« Reply #34 on: July 05, 2019, 01:47:43 am »
I thought he wanted additional chips to fill blank spots on the board, not to replace suspected faulty parts?

I've seen a lot of faulty SRAM chips on old arcade games but those are mostly 2114's.

Oh I see now, both wraper and kjeltthought led me to think this was a repair. Kjelt mentioned Richard would have to "unsolder" the chips himself. But richard says he wants to upgrade and that the device is working, my bad for skimming the replies. so ignore previous message. I have never had a bad SRAM even once on any repair.
I am just chock full of failtard sauce today  :palm:
« Last Edit: July 05, 2019, 10:01:36 pm by chickenHeadKnob »
 

Online RichardMTopic starter

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Re: Trying to find old 8k sram chips for HP-75c calculator pod
« Reply #35 on: July 05, 2019, 02:34:33 am »
Correct. I am just filling empty spaces. I have used 5 x new 8k chips with 55ns speed and they work fine.

https://au.mouser.com/ProductDetail/Alliance-Memory/AS6C6264-55SIN?qs=LD2UibpCYJowQ%252BJQYivAeg==

Thanks everyone.
 

Offline james_s

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Re: Trying to find old 8k sram chips for HP-75c calculator pod
« Reply #36 on: July 05, 2019, 06:36:14 pm »
He said he would have to unsolder the SRAM chips from the scrap board he is offering for salvage, not from the HP.

I think newer SRAMs are quite a bit more reliable than the ones made in the 1970s and early 80s. RAM is one of the most common failures I encounter on arcade games.
 


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