[GreenKeys] ST-8000 Memory Backup Replacement Recommendation

[W2HX]

Maybe check this out
https://www.tindie.com/products/tebo/dallas-ds1220-replacement-without-battery-2/



73 Eugene W2HX
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From: greenkeys-bounces at mailman.qth.net <greenkeys-bounces at mailman.qth.net> On Behalf Of Dino Papas
Sent: Saturday, September 9, 2023 12:53 PM
To: Mail List - Green Keys <greenkeys at mailman.qth.net>
Subject: [GreenKeys] ST-8000 Memory Backup Replacement Recommendation

To those of you who might still be using the Hal ST-8000 HF modem….historically the eight memory settings for shift/baud rates have been maintained by a Dallas DS1220 type non-volatile RAM device.  The IC style device contains a small lithium battery that maintains the data when disconnected from the +5 VDC supply pin.  Those backup batteries have a useful life of about 10 years and the internal battery does not recharge.

Back around 2007 I replaced the two Dallas chips in my ST-8Ks; the originals had date codes of 1986 or 1987 as I recall.  At that time I purchased the new chips direct from Dallas.  So those two units are now getting toward exhausting their battery energy even though they are still functional.

Although DS1220’s are still available I decided to preemptively look for a substitute that wouldn’t be tied to a internal battery…I’d seen some pages on the web where folks had actually done surgery of old units, which are potted, trying to substitute a coin cell for the internal battery but that was a bit too Rube Goldberg for me.

The DS1220 is still available and an interesting note I found in the device’s data sheet is that they are now shipped without the internal battery connected to maximize shelf life and that the first time 5VDC is applied the battery is engaged…but I still wanted a better long-term substitute.

Recently I found a seller on Tindie who selling a small 24-pin PCB using the Cypress FM16W08 F-RAM chip, a pin compatible device that replaces the Dallas DS1220 NVRAM on a small PCB but without the need of a internal or external backup battery.  Apparently the Cypress device is rated to last for 151 year retention cycle!

You can see the device data sheet at:

https://www.infineon.com/dgdl/Infineon-FM16W08_64-Kbit_(8_K_8)_Wide_Voltage_Bytewide_F-RAM_Memory-DataSheet-v07_00-EN.pdf?fileId=8ac78c8c7d0d8da4017d0ebdeb9030f2

The seller Tobias Bonetti on Tindie (who is a great guy by the way!) offers his board in three configurations, see:

https://www.tindie.com/products/tebo/dallas-ds1220-replacement-without-battery-2/

The Swiss postal service got the replacements to me in less than a week.

One thing I learned the hard way was that 0.1” Arduino style headers will not work with the circular IC pin sockets in the ST-8K (thank goodness for my Hakko desoldering gun).  I actually ended up using cut off component leads to tack solder the PCB down at the four corners and then used more leads for each pin.  This actually worked quite well (hams gotta be inventive!) but I have in the interim gotten a supply of the correct circular header pins that I will install if required.

Finally, if you replace the DS1220 with either a new unit or this substitute be careful inserting it into the socket as the socket actually has 2 more holes than the number of pins on the chip....check the orientation BEFORE you take the old one out so you put the replacement chip in correctly!

Hope this helps!

73 - Dino KLØS
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