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TR808 memory problem Drum Machines & Samplers
Old 31st August 2011
  #1
Gear Head
 
krikorola's Avatar
TR808 memory problem

Hello,

i have a problem with my TR808.
The accent, bass drum, snare drum and low tom cannot be writen in the patern anymore. I can play them manually, even though they don't react so good to the triggering.
all other sounds are behaving normally.

Has anyone encountered a similar problem?

Are the NEC 1024k SRAM [NEC1024k] [RS444] memory modules responsible for the pattern writing?

Thanks
K
Old 31st August 2011
  #2
Gear Head
 
krikorola's Avatar
Ok the modules are indeed responsible.
just need to find now if the module itself is dead, or if it's a resistor around it.

extract from page 4 of the 808 service manual

Old 31st August 2011
  #3
Lives for gear
Very rarely does a resistor go bad..

(I have had it happen tho)

It could be the ram.. It also could be an ic that indexes the ram.
Old 31st August 2011
  #4
Gear Head
 
krikorola's Avatar
Quote:
Originally Posted by Futureman84 View Post
It also could be an ic that indexes the ram.
if this is the problem it might be really difficult to fix, right?
Old 31st August 2011
  #5
Lives for gear
Quote:
Originally Posted by krikorola View Post
if this is the problem it might be really difficult to fix, right?
No.

I don't have the schems here, but it'll prob be a 4011 or something similar. About $3.

I'll have a look tonight, and get back to you.
Old 9th October 2011
  #6
Gear Head
 
krikorola's Avatar
It seems it might be more related to the SRAM.
The IC5 (TC4011BP) indexes the 4 SRAM modules (uPD444C) named IC7 to IC10, from what i understand it is unlikely that only one SRAM module would suffer from a malfunctioning IC5.
All four would be acting wrong if it was the case, in my case only the RAM IC7 is not working right.
Old 11th February 2012
  #7
Gear Head
 
krikorola's Avatar
Fixed! that was the uPD444C, the IC7 more exactly.
Old 18th November 2012
  #8
Here for the gear
 
Rhythm Machine's Avatar
Quote:
Originally Posted by krikorola View Post
Fixed! that was the uPD444C, the IC7 more exactly.
My 808 has the same problem. Can you elaborate as to exactly what the fix entailed? Is it as simple as getting a new RAM module and replacing the old one? If that's the case was it soldered or socketed? Does the ram need to have anything written to it beforehand or does a fresh blank chip do the trick? Still getting a handle on the 808 so excuse any misused terminology. Thanks!
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