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Akai S900 help
Old 2nd August 2012
  #61
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ernest1970's Avatar
 
🎧 5 years
Hi guys,

I have the same problem with my S900, running the ram test shows code: DK10.

I started change some chips, and this is my list of error codes:

DK08 = IC57
DK09 = IC58
DJ06 = IC63
DK11 = IC64
DK12 = IC65

DK10 = ?? :(

i hope find a way to locate the bad RAM.

Bye!
Old 9th August 2012
  #62
Gear Head
 
midnightmarauder's Avatar
 
🎧 10 years
After some hours working with this, consulting my engineer friend Hans, we have some progress.

My friend reprogrammed a silent sample transfered with Omniflop to consisting only of 1's. I scoped the Digital Out (pin 14) of the 28 RAM ic's while running the sample and found that IC45-IC60 (located in the two senter coloumns) gives a very different signal then the 12 RAM ic's located in the outer coloumns. Looking at what we already known locations of DK-messages (except some of them :S ) I suggested that the outer coloumn RAM's are indicated by DKxx, and the inner are DJxx.

After replacing 4 different "DJ" ic's correctly following the RAM check codes I found that IC45-IC60 = DJ00-DJ15

So now I have RAM OK, but still the clicking sound in the beginning of a full length sample. I don't know, maybe the RAM test won't find the real faulty one, or the fault lies elsewhere. Maybe I'll replace them all now that I've got the hang of it...
Old 10th August 2012
  #63
Gear Nut
 
deep_disco's Avatar
 
🎧 10 years
Sad to see so many S900s struggling these days.

Hate to cross reference posts, but I'm having a bit of trouble with my unit, as described in this thread here:

https://gearspace.com/board/electron...-response.html

If any of you experienced S-series sampler heads can help me out, I would be so grateful.
Old 10th August 2012 | Show parent
  #64
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ernest1970's Avatar
 
🎧 5 years
Hi,

If you remove an outer ram and turn on the s900 it works, but if you remove a RAM IC45-IC60 will not start, and blink the leds. I think the inner rams (IC45-IC60) are used, in part, by the OS.



Bye.
Old 10th August 2012 | Show parent
  #65
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midnightmarauder's Avatar
 
🎧 10 years
Quote:
Originally Posted by ernest1970 ➡️
Hi,

If you remove an outer ram and turn on the s900 it works, but if you remove a RAM IC45-IC60 will not start, and blink the leds. I think the inner rams (IC45-IC60) are used, in part, by the OS.



Bye.
I experienced this as well, cutting pin 2 on IC58 led to OS not loading.
Old 16th November 2012 | Show parent
  #66
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🎧 5 years
If I have a "bad bit dk14" is enough to replace the IC67?
Old 10th April 2013
  #67
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🎧 5 years
First post here!

I've been starting to use my good old s900 again lately, but some times it freezes when im trying to sample. Sometimes i can sample 10 seconds, but with crackling noise. Other times it freezes after a 0,5 sec sample. Im not shure, but it seems like it gets worse the longer the sampler is on. The other day i left it on for about 5 hours. When I came back all I could see was strange numbers.
I did run the mem test "bad bit dk10". I have ordered 28 new ic's, but I don't want to replace them all if i dont have to.
Does anyone have any new information about the bad bit messages?
I tried at akai support with no luck. (not that i really thought they would help me either). Bastards! Here is what they said: Akai s900 Bad Ram Ic (DK10)

I might change all the ic's and will report back how it turns out, but it will take some time.
Old 19th April 2013
  #68
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ernest1970's Avatar
 
🎧 5 years
hello
I have the same problem, and I could not find the faulty chip

bye!
Old 30th April 2013 | Show parent
  #69
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🎧 5 years
I picked up an S900 a couple of years ago with a Bad Ram Bit DJ10 message and nothing after.

This is a very useful thread, thanks everyone. I have 2 S900s that don't work, the other just has black blocks on the display and thats all I get from it. Was going to canibalise it for the Bad Ram one but now I'll get that working (using the info from this thread and new parts) and swap various parts between the two until I find the issue.

I'll post my progession with the Bad Ram S900 in case it is any help...
Old 13th May 2013 | Show parent
  #70
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ernest1970's Avatar
 
🎧 5 years
Quote:
Originally Posted by Lazster ➡️
I picked up an S900 a couple of years ago with a Bad Ram Bit DJ10 message and nothing after.

This is a very useful thread, thanks everyone. I have 2 S900s that don't work, the other just has black blocks on the display and thats all I get from it. Was going to canibalise it for the Bad Ram one but now I'll get that working (using the info from this thread and new parts) and swap various parts between the two until I find the issue.

I'll post my progession with the Bad Ram S900 in case it is any help...
Thanks!!!!
Old 3rd June 2013 | Show parent
  #71
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ernest1970's Avatar
 
🎧 5 years
Quote:
Originally Posted by Lazster ➡️
I picked up an S900 a couple of years ago with a Bad Ram Bit DJ10 message and nothing after.

This is a very useful thread, thanks everyone. I have 2 S900s that don't work, the other just has black blocks on the display and thats all I get from it. Was going to canibalise it for the Bad Ram one but now I'll get that working (using the info from this thread and new parts) and swap various parts between the two until I find the issue.

I'll post my progession with the Bad Ram S900 in case it is any help...
Do you have any progress?
Old 6th January 2015 | Show parent
  #72
Gear Nut
 
🎧 5 years
Bump cuz im getting a bad dk12 code too
Old 6th January 2015
  #73
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kazper's Avatar
 
🎧 15 years
I don't know how many ram chips are in the S-900 and if there available still but it may be just worth it to pull em all and install sockets then plug in some new ones and give it a try. Worth a shot if there is a semi common equivilent ram chip still available on the cheap.
Old 14th September 2015
  #74
Gear Maniac
 
🎧 5 years
I tried to to replace a ram chip dj04 today on my s900.

I made an assumption that it was ic49 given the results earlier in this thread and since fitting a socket and new ram chip the akai doesn't start up anymore.

All the LEDs on the front come on and the screen lights up but that's it. Hoping it's just a lose connection somewhere as I was extremely careful in the repair and I can't see any damage anywhere. I'm getting continuity with each of the ram ic pins and the corresponding solder on the bottom of the board so I think the socket and ic are installed correctly. (I've tried other chips and the one I desoldered with no change)

The cpu board is getting 5v's but I'm not really sure where to start testing.

Any ideas?
Old 19th January 2018
  #75
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🎧 5 years
It takes eight 1-bit 256k D-RAMs to makes a standard 256KB chunk of memory, four to make 128KB, two to make 64KB or one to make 32KB (math: 256Kbits divided by 8 bits per byte = 32KBytes).

The Akai has 28 D-RAMs, therefore it has 896KB total. And the response some of you are going to give is: "You're an idiot! The Akai S900 only has 750K! It says so in the specs!"

That's because the specs are only regarding sample memory, not actual system RAM, and it's using "kilo" as traditional 1000 instead of the digital kilo of 1024 -- 768KB is 3/4 of 1024KB. In other words, it's 75% of a megabyte = 750 thousand out of a million = 750K. Technically, it would be 768 *kibi*bytes and literally 750 *kilo*bytes, so--although entirely confusing--Akai isn't exactly wrong.

24 of the DRAMs are allocated as sample storage (or wave memory) and 4 of the DRAMs as OS (or work memory).

The S950 uses the same configuration but uses DRAMs that are four times as large as the S900 (4-bit instead of 1-bit), so there are only 7 RAM chips in the stock S950 instead of the 28 in the S900 -- a quarter of the ICs for the same amount of RAM.

In the S950, one D-RAM is allocated as work memory and the remaining six are sample memory.

As far as Akai S900 RAM testing and troubleshooting is concerned, the assumption that DK and DJ are both 00~15 is obviously wrong as that would make 32 RAM chips and there are only 28 total. Therefore DK and DJ cannot both be numbered as such. That means four numbers will not be present -- if there are only two letters (K/J) then there are either 14 per letter, or 16 of one and 12 of another. I would assume something like DK0~3 are missing.
Old 20th January 2018 | Show parent
  #76
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🎧 5 years
Disclaimer: Keep in mind that I've never actually tested these notions, so it's all (an educated and researched) speculation and the information could be invalid. But this is my take on unraveling the great mystery from the comfort of my armchair.

AKAI S900 DRAM THEORY

Any given DRAM can be found by a combination of its address/data line and its column address. In other words, each DRAM is a point in a matrix where its assigned column address strobe (CAS) and its specific address/data line intersect.

The address/data lines are numbered 0~15 (16 total) and since the DRAMs in the S900 are 1-bit then there should only be one address/data line per DRAM,
as opposed to the S950 which uses 4-bit DRAM and therefore has four address/data lines per DRAM.

As for CAS, there should only be two groups: CAS0 and CAS1.

So, the intersection of CAS0 and AD0 should land us at the first DRAM in the OS RAM space, and CAS0/AD1 should land us at the second OS DRAM, CAS0/AD2 at the third OS DRAM, and CAS0/AD3 at the fourth and last OS DRAM.

The same idea applies to the wave sample DRAMs with varying CAS and address/data combinations.

In short, to answer a rhetorical question posed in my previous post, the DRAMs should be in one group of 16, and one group of 12.

Reference the chart below:

Work Memory is AD0~AD3 [CAS0]
Wave Group 1 is AD4~AD07 [CAS0]
Wave Group 2 is AD8~AD11 [CAS0]
Wave Group 3 is AD12~AD15 [CAS0]

Wave Group 4 is AD4~AD7 [CAS1]
Wave Group 5 is AD8~AD11 [CAS1]
Wave Group 6 is AD12~AD15 [CAS1]

The CAS "grouping" the OS DRAMs belong to is assigned address/data lines 0~15 (16 total). The other CAS "grouping" is only 4~15 (12 total), and--since 16+12=28--this accounts for all 28 DRAM chips.

CAS assignment cannot tell us definitively if it is sample or OS RAM, but if we find a DRAM with CAS1 then we can definitively declare it is sample RAM.

As CAS0 comes before CAS1--just as J comes before K--it could be assumed that DRAM group 'J' [DJ] is equivalent to CAS0 and DRAM group 'K' is equivalent to CAS1.

From there we can speculate that DJ0~DJ3 would be the four DRAMs that form the OS RAM, DJ4~7 are Wave Group 1, DJ8~11 are Wave Group 2, and DJ12~15 are Wave Group 3. This is supported by the fact that the S900 fails to boot when certain DJ chips are removed or disabled; while the S900 either may or may not boot with certain portions of sample RAM missing (indeterminate at present), it is 100% definite that the S900 cannot possibly boot if a portion of its OS RAM is missing.

Also, since the RAM test cannot be run if the OS cannot boot, it's possible that the RAM test might not be able to report a bad DJ0, DJ1, DJ2, or DJ3 code. Likewise, if DK does not contain address lines 0~3 then it is impossible for the RAM test to ever report a bad DK0, DK1, DK2, or DK3. Therefore, all errors reported by the RAM test are fairly likely to be exclusively at address lines 4~15--regardless if DJ or DK.

That leaves the million dollar question: How can it be determined which DRAM (ICxx) is assigned to each error code?

First step is to do a continuity test between the CAS pin on one DRAM (an arbitrarily picked 'control' DRAM) and the CAS pin on all the other DRAMs (the 'experiment' DRAMs). Any DRAMs sharing continuity are all part of the same CAS line, so if the 'control' DRAM has continuity with 16 other DRAMs then it is part of the CAS0 line (DJ group) and if it instead shares continuity with only 12 other DRAMs then it is part of the CAS1 line (DK group). Any DRAMs not sharing continuity can all be automatically grouped into the opposite CAS of the 'control' DRAM's CAS group (CAS0 vs CAS1 or vice versa).

Second step is to find something which has the AD lines (AD0~AD15), so if the RAM test error code is DK4 (for example) then find the AD4 pin and continuity test the address/data pin on all the DRAMs which were grouped into DK/CAS1. There should only be one DRAM in that CAS group which has continuity with that specific address/data pin.

Fill in the newly discovered IC # into an error-code-to-IC table and repeat the process for any unknown DRAMs. The choices and test time will get smaller and smaller the more DRAM locations are known, and the selection of unknown chips dwindles. Eventually the table will be complete and definitive.


TECHNICAL SPECIFICS


Where are the proper pins for CAS and address/data on the DRAMs?

For CAS on the 1-bit DRAMs, check pin 15.
For A/D on the 1-bit DRAMs, check pin 14.


Where inside the S900 can the AD lines be found and tested?

On the S950 this is easy because IC1 contains them all. On the S900 this is trickier:

Find J103 (one of the ribbon connectors leading off the CPU PCB and on to another PCB). All the even pins (2~24) correspond to AD4~AD15. So pin 2 of J103 carries AD4, pin 4 of J103 carries AD5, etc.

A slight problem is that AD0~3 are used only on the CPU board (therefore omitted from the J103 header because the signals never need to be sent to any daughter PCBs--quite practical, really), but this actually opens up an easy way to quickly discover all the OS DRAMs. Probe the DRAM A/D pin and slowly rake the even pins 2~24 of J103 for continuity. If no pins have continuity with the DRAMs A/D pin then it's an OS DRAM.

Hint: Use the underside of the J103 header (the one with the solder points/peaks) for this so that removing the ribbon cable is not necessary.

Also, once you find one OS DRAM then whatever is connected to its CAS pin is also on that same CAS--for a group total of 16. Quickly finding all four OS DRAMs will drop the total number of DRAMs that need to be CAS tested from 28 to 24 since all OS chips will be on the same CAS. Finding out which CAS each sample DRAM is assigned to requires direct comparison, however.


But what about AD0~3?

Remember that AD0~3 only applies to CAS0 and--more specifically--the OS DRAMs. If there is a problem with any of the OS DRAMs then the S900 probably won't boot, so the RAM test cannot be run. Even if it does, the RAM test would be suspect anyway.

Still, AD0~3 should be able to be figured out based on other devices on the CPU board, such as the two EPROM chips for the OS. Either 27128 EPROM on the CPU board should have pins 11, 12, 13 & 15 connected to the needed AD lines.

27128 pinout:
pin 11 - Q0 - AD0
pin 12 - Q1 - AD1
pin 13 - Q2 - AD2
pin 15 - Q3 - AD3
pin 16 - Q4 - AD4
pin 17 - Q5 - AD5
pin 18 - Q6 - AD6
pin 19 - Q7 - AD7

As a secondary--and perhaps preferable--method for finding the OS RAM easily, hold one continuity probe on the OS firmware (either one -- LSB or MSB) pin 11 and sequentially touch each DRAM pin 14 with the other continuity probe. The only DRAM with continuity will be OS DRAM 1. Repeat for pins 12, 13, & 15 on the OS firmware, and the remaining three OS DRAMs will be located.


"Yo, man... just give us the right codes! I need to fix my bad RAM bit DK10!"

Maybe sometime in the near-ish future, time permitting. As of yet, I've only worked out a solid potential theory for people to track down their own issues or try constructing the error-to-IC "master table" everyone has been seeking. Once the table has been constructed and published, RAM test codes and proper repair should only be a 30-60 minute issue instead of a multiple decades old mystery involving wizardry and/or luck.

If someone actually confirms this information is correct by constructing the table, do please be a dear and share it publicly.
Old 22nd January 2018 | Show parent
  #77
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🎧 5 years
My DRAM theory appears to have fallen apart somewhere...

Measured all the CAS assignments today and they're broken into four groups, not the expected two.

IC45~52 are grouped, IC53~60 are grouped, IC61~68 are grouped, and IC69~72 are grouped. This follows the PCB layout exactly, as those are all grouped the same way as the ICs are physically -- when looked at in their numeric sequence, they form four (three and a half, really...) vertical columns.

IC45~48 are probably the OS DRAMs. IC45 is tied to AD0 of the LSB EPROM, and IC45 is the starting number of the DRAMs, so it makes perfect sense that it would be at the start of the memory assignment. IC46 is AD1, IC47 is AD2, and IC48 is AD3, so again, they progress logically in a physical sense, starting from the bottom of the PCB.

IC49~52 need to be puzzled out further. Since they're on the same CAS as IC45~48 then they should not be AD0, 1, 2, or 3 but the scheme isn't clear yet.

Still, it does agree with the suggested idea that the two inner most columns are DJ0~15. It seems that DK would therefore start on the right-most column at IC61 and then finish with the left-most half-column.

I was expecting something much closer to how the S950 works, but there seems to be a significant departure. Interesting.

IC88 is the Column Address Selector, so:

pin 06 - 2Y = IC45~52 (CAS0?)
pin 03 - 1Y = IC53~60 (CAS1?)
pin 11 - 4Y = IC61~68 (CAS2?)
pin 08 - 3Y = IC69~72 (CAS3?)

A/D Selectors:

IC79 - TC74HC257P

Nibble A Inputs:
pin 2 = IC49
pin 5 = IC50
pin 11 = IC51
pin 14 = IC52

Nibble B Inputs:
pin 3 = IC69
pin 6 = IC70
pin 10 = IC71
pin 13 = IC72

IC80 - TC74HC257P

Nibble A Inputs:
pin 2 = IC53
pin 5 = IC54
pin 11 = IC55
pin 14 = IC56

Nibble B Inputs:
pin 3 = IC61
pin 6 = IC62
pin 10 = IC63
pin 13 = IC64

IC81 - TC74HC257P

Nibble A Input:
pin 2 = IC57
pin 5 = IC58
pin 11 = IC59
pin 14 = IC60

Nibble B Input:
pin 3 = IC65
pin 6 = IC66
pin 10 = IC67
pin 13 = IC68

Will work on this more as time permits.

1/23/18 Update

I still believe that only the OS DRAMs are accessed by AD0~3, so the DRAM layout may be something more like this:

Work Memory is AD0~AD3 [CAS0] / Wave Group 1 is AD4~AD07 [CAS0]
Wave Group 2 is AD8~AD11 [CAS1] / Wave Group 3 is AD12~AD15 [CAS1]

Wave Group 4 is AD4~AD7 [CAS2] / Wave Group 5 is AD8~AD11 [CAS2]
Wave Group 6 is AD12~AD15 [CAS3]

Next step is to trace the DRAMs back through the TC74HC257P ICs to see their final destinations. Sad thing is--as one of the previous techs in this thread suggested--there might be no logical order of the codes to the memory layout. It could be that they're arbitrarily assigned and there will be no way to find the codes except for testing each DRAM failure one-by-one. Engineers and programmers don't tend to do strange things like that unless they're pushed by higher-ups, so I'm still going to believe there's an order to them.

1/24/18 Update

Unscrambled the data outputs from the DRAMs (74HC2257P listing above) to clearly show their groupings per nibble. It's of note that each nibble is formed by a numerically sensible grouping of 4 sequentially numbered ICs. In other words, still no real reason for the apparently scattered error codes, but it would make sense if the codes were broken into groups of 4 and then rearranged. Such as:

IC45~48 = DJ0~3 (these don't go through any multiplexing, so I think they're exactly as they appear to be)

IC49~52 = DJ4~7
IC69~72 = DJ8~11

IC53~56 = DJ12~15
IC61~64 = DK4~7

IC57~60 = DK8~11
IC65~68 = DK12~15

This seems semi-consistent with the reported error codes so far, but still off. IC 45~56 would still be DJ, although not 57~60, but don't think they actually tested one-by-one and it was just a conclusion reached by testing the first few (57~60 could easily have been skipped), so that's probably not conclusive. Also, I feel pretty confident IC65~68 is correct.

I'm wondering if the error codes reported thus far are 100% correct. I have a feeling that brute forcing the codes will come first, and then the logical pattern will present itself... working backwards.

After following the multiplexers connected to the AD lines to/from the DRAMs, they (unsurprisingly) go back to the CPU (IC1).

IC1:

pin 12 (AD4) = Y0 (pin 4) input from multiplexer IC79
pin 11 (AD5) = Y1 (pin 7)
pin 10 (AD6) = Y2 (pin 9)
pin 9 (AD7) = Y3 (pin 12)

pin 8 (AD8) = Y0 (pin 4) input from multiplexer IC80
pin 7 (AD9) = Y1 (pin 7)
pin 6 (AD10) = Y2 (pin 9)
pin 5 (AD11) = Y3 (pin 12)

pin 4 (AD12) = Y0 (pin 4) input from multiplexer IC81
pin 3 (AD13) = Y1 (pin 7)
pin 2 (AD14) = Y2 (pin 9)
pin 39 (AD15) = Y3 (pin 12)

So it looks as if AD0~3 is fed by IC45~48. AD4~7 is toggled between IC49~52 and IC69~72, AD8~11 is toggled between IC53~56 and IC61~64, and AD12~15 is toggled between IC57~60 and IC65~68.

I'm guessing that means IC49~52 + IC53~56 + IC57~60 form one 12-bit word, and IC69~72 + IC61~64 + IC65~68 form the next 12-bit word. It seems odd that it's all sequential except for IC69~72 coming ahead of IC61~68, but that might have been a board layout thing. It doesn't really matter where the data is written so long as it's read back from the same place, so maybe it was just the most convenient way to lay the traces to the multiplexer.

If so:
IC49~52 = DJ4~7
IC53~56 = DJ8~11
IC57~60 = DJ12~15

IC69~72 = DK4~7
IC61~64 = DK8~11
IC65~68 = DK12~15

This seems really close, or correct. One of the original posters said DK07 was IC61, but I believe this was reported improperly. IC61 should in fact be DK08, as I have just tested it as a match.

I believe some of the error codes reported are because other memory errors are either being masked or unmasked. Since the RAM test cannot report multiple events, the RAM test stops on the first error reached. If there are multiple errors then the code that appears tied to a particular chip will change depending on what other chip(s) are replaced or made faulty. For example, if DK08 and DK15 are both bad, it will only report on DK08. Perhaps this phenomenon has confused things.

For the poster that was looking for DK10, I believe it is IC63. I don't know the testing order attempted in that case, but I have a feeling that (in general, if not always) low DK errors mask high DK errors, and DK errors mask DJ errors. More specifically, the check appears to run DK low to DK high and then DJ high to DJ low.

As an example, if you have a bad DK00 then every single other bad DRAM will not be detected until DK00 is repaired. If DK00 is repaired then a bad DK10 will mask DK11~15 and DJ0~15. Fix the bad DK10 and you might have a bad DJ12 which will mask DJ00~11. Repair the DJ12 and you might have a bad DJ04. Repair the bad DJ04 and hopefully your board is fixed

So... prior in the thread, someone was trying to figure out DK10. I believe they actually found DK10 and fixed it but didn't realize it because it still threw a DJ error. But... if your error is a DJ then you can assume all your DKs are okay -- at least according to my theory. If I'm correct then low DJ errors (which are not DJ0~3 or otherwise cause the OS to halt) are the best to have because it should mean most of your DRAMs are intact. If you have a low DK error then you might be replacing only one chip, or potentially quite a few.

I would suspect a great many S900 machines have bad RAM that has gone unfixed and even unnoticed -- I would even guess a large majority of S900s are not operating 100% properly. There's a huge leeway for faulty DRAMs in the S900, and you could probably have 4-5 bad chips and not even really notice depending on where it is in memory space and what is being sampled. Pretty crazy, really.
Old 22nd January 2018
  #78
Gear Maniac
 
joostoftoday's Avatar
 
🎧 5 years
Thanks a lot for the interesting insight! Fascinating read. Do you have any information about the S900 CPU? I always thought it would be cool, to do some modifications for the S900
Old 22nd January 2018 | Show parent
  #79
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🎧 5 years
Quote:
Originally Posted by joostoftoday ➡️
Thanks a lot for the interesting insight! Fascinating read. Do you have any information about the S900 CPU? I always thought it would be cool, to do some modifications for the S900
I just wish I was making more progress! I was convinced I had enough to go on, but it hasn't been the clear sailing that I expected. I'm no expert, to be clear.

Pinout of the CPU: Pinouts - V30 family

The CPU is more-or-less the NEC version of the Intel 8086, so being familiar with that would help. I haven't taken a close look at it, but I have dumped the 1.2a OS firmware as well as the three other EPROMs "above" the DRAM section on the CPU board.

I'm not sure what they do, but they're all the exact same data -- seems a waste of space. They seem to be some kind of tables for voice expression or something, so I guess Akai wanted to leave themselves latitude for tweaking things individually, if they needed to.

It's an interesting case because even though the S950 and the S900 are very similar, they also have fairly big differences in layout.

I'm still plugging away at it, regardless.
Old 4th April 2018 | Show parent
  #80
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🎧 5 years
Akai S900 BAD RAM (D-RAM) BIT CODES

After further research, I can state these are 100% accurate and definitive. So, here's a nice table for reading convenience:

IC45 = DJ0
IC46 = DJ1
IC47 = DJ2
IC48 = DJ3

IC49 = DJ4
IC50 = DJ5
IC51 = DJ6
IC52 = DJ7

IC53 = DJ8
IC54 = DJ9
IC55 = DJ10
IC56 = DJ11
IC57 = DJ12
IC58 = DJ13
IC59 = DJ14
IC60 = DJ15

IC61 = DK8
IC62 = DK9
IC63 = DK10
IC64 = DK11
IC65 = DK12
IC66 = DK13
IC67 = DK14
IC68 = DK15

IC69 = DK4
IC70 = DK5
IC71 = DK6
IC72 = DK7
Old 5th July 2019 | Show parent
  #81
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adhmzaiusz's Avatar
 
🎧 10 years
Quote:
Originally Posted by Rasputin1916 ➡️
Akai S900 BAD RAM (D-RAM) BIT CODES

After further research, I can state these are 100% accurate and definitive. So, here's a nice table for reading convenience:

IC45 = DJ0
IC46 = DJ1
IC47 = DJ2
IC48 = DJ3

IC49 = DJ4
IC50 = DJ5
IC51 = DJ6
IC52 = DJ7

IC53 = DJ8
IC54 = DJ9
IC55 = DJ10
IC56 = DJ11
IC57 = DJ12
IC58 = DJ13
IC59 = DJ14
IC60 = DJ15

IC61 = DK8
IC62 = DK9
IC63 = DK10
IC64 = DK11
IC65 = DK12
IC66 = DK13
IC67 = DK14
IC68 = DK15

IC69 = DK4
IC70 = DK5
IC71 = DK6
IC72 = DK7
Yup, excellent work, I can verify that this is true. Thank you so much for posting this. My s900 has been on the shelf for years because of the bad ram. I had 4 different chips that were bad in no particular order. I really wish that the s900 would tell you a list of chips that're bad all at the same time though. It's a little annoying to replace a chip... put it back together... see new bad chip in ram test... disassemble... replace chip... repeat repeat repeat. Either way this did solve my problem, thank you very much!
Old 5th July 2019
  #82
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Funnily enough I've just joined GS because of this very subject. This thread has been fascinating and invaluable - the list of ICs is entirely accurate, I've fixed three 'bad' RAM chips with replacements, and I now get a RAM OK message after running the test. But despite that, the last third or so of my sample memory is distorted, when recording the full memory at 16000 bandwidth. I can't figure out which chips might need replacing, and want to try to avoid removing everything. Are there any methods for identifying problems beyond the memory test?
Old 7th August 2019 | Show parent
  #83
Gear Addict
 
🎧 5 years
Quote:
Originally Posted by adhmzaiusz ➡️
Yup, excellent work, I can verify that this is true. Thank you so much for posting this. My s900 has been on the shelf for years because of the bad ram. I had 4 different chips that were bad in no particular order. I really wish that the s900 would tell you a list of chips that're bad all at the same time though. It's a little annoying to replace a chip... put it back together... see new bad chip in ram test... disassemble... replace chip... repeat repeat repeat. Either way this did solve my problem, thank you very much!
Good to know of your experience. And were the replacement chips the IC MN41256-12 found on eBay?

I’m thinking of doing all my chips but just doing my research for it now, so any summary of your process would be really helpful. Thanks in advance.
Old 7th August 2019 | Show parent
  #84
Lives for gear
 
adhmzaiusz's Avatar
 
🎧 10 years
Quote:
Originally Posted by millionmiles ➡️
Good to know of your experience. And were the replacement chips the IC MN41256-12 found on eBay?

I’m thinking of doing all my chips but just doing my research for it now, so any summary of your process would be really helpful. Thanks in advance.
The ones on eBay should in theory work, the part number looks right. I just grabbed ones from a local electronics surplus shop.

If you’re considering doing all of the chips it’ll be a pretty big job. There’s a lot of them, someone provided a count earlier in this thread. It would probably be less work to just replace only the bad chip(s) according to the test mode. The only tedious thing about it is you have to access the lower circuit board and each time and connect/disconnect about 6 different connectors. The screen only tells you one bad chip at a time but you might be lucky and only have one.
Old 7th August 2019 | Show parent
  #85
Gear Addict
 
🎧 5 years
Quote:
Originally Posted by adhmzaiusz ➡️
The ones on eBay should in theory work, the part number looks right. I just grabbed ones from a local electronics surplus shop.

If you’re considering doing all of the chips it’ll be a pretty big job. There’s a lot of them, someone provided a count earlier in this thread. It would probably be less work to just replace only the bad chip(s) according to the test mode. The only tedious thing about it is you have to access the lower circuit board and each time and connect/disconnect about 6 different connectors. The screen only tells you one bad chip at a time but you might be lucky and only have one.
Thanks for the response.

Seems to be a chip by chip thing (if the s900 only reports the first bad IC).
Well, let's see how far I get when i roll up the sleeves...
Old 5th December 2019
  #86
Lives for gear
 
Fanu's Avatar
So did anyone find out about the correct replacement chips?
Got a faulty DK10 on mine.
Old 5th December 2019 | Show parent
  #87
Gear Addict
 
🎧 5 years
Quote:
Originally Posted by Fanu ➡️
So did anyone find out about the correct replacement chips?
Got a faulty DK10 on mine.
The RAM ICs are any 256k x1 DRAM DIP16 package ie: generic 41256. Speeds from 120 to 150 nanoseconds will work fine.

e.g. here are some sample IC numbers:

- IC MN41256-12
- IC 41256-120

In the end tho, I got them from the legendary Andrew Zuppa from DopeShtOnly. That was much easier to deal with, and they were extremely cheap.
Old 14th December 2019
  #88
Lives for gear
 
Fanu's Avatar
Thanks, Millionmiles!
Bought 10 of those.
Just fixed one, and now seeing another chip listed as bad.
Now that I know it works, will fix the rest on my holiday.
Yay!
Old 29th December 2019
  #89
Lives for gear
 
🎧 5 years
To be certain which RAM chip is faulty, you can use this memory tester:

http://www.amibay.com/showthread.php...r-C64-and-more

I have successfully identified bad chips using it.
Old 10th August 2020 | Show parent
  #90
Here for the gear
 
Hey, I’m getting the error DK15. The confusing thing to me is, that the horrid sound appears at the end of the sample always. If it’s a short sample like the TONE sample, you hear the noise almost instantly. If I record a 10 sec sample I only hear it after maybe 8 seconds or so.
This doesn’t seem to be in line with how people describe their errors though, stating that different chips lead to an error at a different section of the wave sample. My error is always at the end. I’ve replaced an IC to fix DK13 already, and now awaiting some chips to replace The IC for DK15.
Worried it might be a different issue if not related to a fixed point in sample memory. Anyone have any ideas on this?
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