Author Topic: Looking for SRAM substitution...  (Read 5249 times)

Projectile

Looking for SRAM substitution...
« on: August 14, 2011, 04:29:25 AM »
Not sure where to find help with this, so I thought I'd post here.

I'm trying to fix a Juno-60 synthesizer that is having some issues: erratic memory bank behavior, attack slider doesn't work, LFO glitches. I'm pretty sure I've narrowed all of these problems down to the logic control side of things. The audio signal path and all of the mechanical parts seem to be working perfectly. I noticed some nasty corrosion on a few ICs, so I figure I'd replace those first, but I'm having trouble finding replacements.

The ones that are giving me the most trouble are the 2 SRAM ICs:

TC5513APL-20

The closest thing I can find is a set of NOS TC5514AP chips on ebay, which look pretty similar from the datasheet, but they want $25 for them, and the seller is overseas. I'd much rather find a cheaper or local alternative, but I don't know the first thing about SRAM. The datasheet says its 4k CMOS static RAM (1024x4) 18pin with 200ns seek time and low power usage.

So, do I have to use this vintage SRAM chip, or is there a drop in replacement I can use? Are there any other substitutions that will work?

I did some searching and it looks like any 2114 sram chip might work as a drop in replacement. I can't find any info on the 5513, but apparently the 5514 is Toshiba's low power version of the standard 2114 chip, and the 5514 is very close to the 5513 as far as specs go, so I assume it will work. Here's the problem I'm having though: I can find cheap 2114N chips all day long, but they all use WAY more power than the 5513. the Toshiba chip only uses 9mA in use and a few microamps when in standby (perfect for retaining memory with a small battery). I can't seem to find any other 2114 chips with this low amount of power usage. I know they must exist since Toshiba can't be the only company that made low power SRAM chips in the 80s. I'm wondering if maybe the 5514 is a later improvement on the 2114 format? In that case I need to find other companies' next generation improvements on the 2114 in order to find something that will work. There are so many devices that used these chips, I'd be really surprised if there weren't drop in replacements out there, but I don't know the first place to look. I need someone with more knowledge on the subject to point me in the right direction. Can anyone give me some help? 

toneman

Re: Looking for SRAM substitution...
« Reply #1 on: August 14, 2011, 01:13:42 PM »
Are U *sure* it's the SRAM chips. 
IIRC, the 2114 was used in the old Paia Programmable Drum set.
Did U check ALL power supply voltages?  Are they ALL within plus/minus point2 to point5 volts.
Did U have a previous power supply voltage surge?
That might have taken out all the +5V logic...so it the CPU is working, the SRAM is probably ok.
With a small SRAM like this, get the datasheet and breadboard a test circuit using DIPswitches.
Maybe use a 4040 counter to step thru the addresses(?)
Hope this helps...Good luck with your repair.
Want a Prophet2000?  Got a keyboard scan problem...
afn
T
TONE to the BONE says:  If youTHINK you got a GOOD deal:  you DID!

Projectile

Re: Looking for SRAM substitution...
« Reply #2 on: August 14, 2011, 03:51:08 PM »
Are U *sure* it's the SRAM chips. 
IIRC, the 2114 was used in the old Paia Programmable Drum set.
Did U check ALL power supply voltages?  Are they ALL within plus/minus point2 to point5 volts.
Did U have a previous power supply voltage surge?
That might have taken out all the +5V logic...so it the CPU is working, the SRAM is probably ok.
With a small SRAM like this, get the datasheet and breadboard a test circuit using DIPswitches.
Maybe use a 4040 counter to step thru the addresses(?)
Hope this helps...Good luck with your repair.
Want a Prophet2000?  Got a keyboard scan problem...
afn
T


Thanks for the advice. I haven't checked the voltages yet, and I don't know this synth's history. It was like this when I got it. The reason I immediately went for replacement was that the chips are really ugly and corroded, so I assumed that was probably the source of the problem.  I figured that once I replace all of the corroded components, if there is still an issue, then I would start checking voltages. Maybe you're right and even though the memory is corroded it might still be okay. I'll try cleaning them up, testing, and re-soldering before I drop the coin on new chips. Thanks.

I'd love a prophet2000, but I don't think I can afford to purchase one atm. Thanks though.

AdamM

Re: Looking for SRAM substitution...
« Reply #3 on: August 16, 2011, 04:16:41 PM »
you could use almost any modern SRAM but you'd have to make up an adapter board so that it appears as a 1024x4 - i.e. only wire up 4 of the data lines, and 10 of the address lines (tie the unused addresses to 0V). Hook up the chip select(s) etc & you should be good to go.

Most modern parts should have much higher speed capability & so will cope with the relatively slow speed of old kit like this.

Alternatively, get an Actel nano FPGA & create your own 1024x4 SRAM - probably overkill & more expensive than your n.o.s. ebay option!