Potential batteryless mods

[kfowler8]

Hey guys.

About a year ago I posted an issue I was having with my battery draining quickly in my MP-1. (http://adadepot.com/index.php?topic=1048.0) A year later and I'm still fighting the problem. I get probably 1-2 months of battery life. I placed an order for a new 6264 ram chip. That should be here today. Perhaps that will fix the issue.

In the mean time I've been looking into the batteryless mod I've seen. You can read some of that here: http://www.kylheku.com/lurker/message/20131111.161931.09863a88.en.html#ada-mp1/

It seems pretty straightforward. In my search though I've found eprom chips that seem to be the exact same size as the stock SRAM chip. So it would be a straight drop-in without having to make a daughter board.

Here's the eprom chip I'm looking at and the data sheet. http://www.ebay.com/itm/Advanced-Micro-Devices-AMD-AM-27C256-UV-EPROM-28-pin-Ceramic-Package-/301851216704?hash=item4647bc0b40:g:4mQAAOSwa-dWnR3r and http://pdf1.alldatasheet.com/datasheet-pdf/view/55434/AMD/AM27C256-255DC.html

I admit I know very little about how these things work. The eprom chip has more memory but I can't believe that would be an issue. I'm a little more concerned with the power feeding the chip. The original mod uses a couple of resistors and a cap. I'm hoping I could make this really easy and just drop in the eprom chip. For $2 plus shipping I'm tempted to just try it assuming I wouldn't damage the MP-1.

What do you think?

[MarshallJMP]

An eprom won't work,the MP-1 can't write eproms since these are programmed with 12.5V and a special programming algorithm.And second the pin layout doesn't match since the RAM has only 12 address lines and the 256 has 14 address lines.Plus there are some other differences.

So you replaced D43 and C137 right?The only that is powered by the battery is the RAM chip and U44 (74HC20,also make sure it's a HC type and not LS)

Another possible thing to use is a NVRAM chip but sometimes they don't work in the mp-1.Plus these have an internal battery which also fails after years of use so it's not much different from how it works now.If the battery fails you have to buy a new NVRAM because you can't replace them.
And another thing is if you get corrupt data inside the NVRAM you need some programmer to reset it.

[kfowler8]

An eprom won't work,the MP-1 can write eproms since these are programmed with 12.5V...

I assume you mean "can't".

I know a couple of others who have use eproms with success. Here's one that was used in the mods I site all though it is different than the one I listed above. STK12C68 Come to think of it is this really an eprom?

I did replace D43 and C137. I'm hoping it's not U44 since that'll be a little more pain to de-solder. I'm going to give the replacement 6264 a shot and see what happens.

Really sucks too because I've been using the MP-1 a lot lately for recording.

Thanks for all the help!

[MarshallJMP]

Yes i meant "can't" ,sorry (already edited this).

You just can't replace a RAM with an eprom,won't work,100% sure.

That STK chip is a NVsRAM,this is not an eprom.I heared about this chip,it's also used as a replacement for RAM memory in pinball machines,but i never used it.This NVram doesn't use a battery but stores the content of the RAM into non volatile memory at power off.At power on it will copy the data from non volatile to RAM.

But it's not a direct plugin,you need to add some stuff (2 resistors and a cap) to make it work,like explained in that link http://www.kylheku.com/lurker/message/20131111.161931.09863a88.en.html#ada-mp1/
So you either have to make a small pcb or implement it on the main board.
Now this leaves one question,what will happen with U44 since it's not powered anymore with the battery.There was a reason why ADA attached it to the backup battery.

[kfowler8]

New ran chip came today. Installed it and seems to work. I'm going to put a fresh battery in and see how long it lasts. Hopefully the new chip cured the problem.

[MarshallJMP]

Ok keep us updated.Let's hope it works.Did you check U44 if it's a HC type?

[kfowler8]

Yes, it is HC. Out of curiosity what's the difference with the LS?

I wrote the date of the new battery on it with a Sharpie. We'll see how long it lasts. If it lasts over two months, I should be good.

[MarshallJMP]

The 74LS is Transistor to Transistor logic. Uses Shottky transistors to reduce the stored charge and get higher switching speeds then with conventional bipolar transistors.
The 74HC uses MOSFET technology. Therefore can operate with wider variety of voltages. Power consumption better then TTL
So in this case they use a HC since the power consumption is lower.

Did you also replaced D42?

[kfowler8]

 Big update. So for some reason the new chip I bought didn't work. It would work for a bit and then look like the memory would get scrambled.

So I decided to go ahead and try the batteryless  mod.  After an initial  screwup of building the daughterboard and having to order some new parts, I finished it last night and guess what? It works! I'll post a full rundown of the parts and everything soon.

[rnolan]

Well done  , look forward to the rundown  >:D :wave: