ARP Quadra computer problem

  • Thread starter Thread starter Blue Jinn
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Blue Jinn

Blue Jinn

Rider of the ARPocalypse
OK, cross posted, but the DIY (because no one else will) ethic is STRONG here.

Anyway, know this is a rare machine. Here is the deal, the 16 programmable switches don't program. The actual function switches still work, and the program change switches appear to change (but not really, mostly just all on or mostly all on) so it doesn't seem that whatever programs were in there are still actually in there.

Also, the pitch for the lead synth scanning mechanism ("interval write") works as well. However, when switching from "Lock" to "Load" the function switches all freeze (basically you're supposed to swith to load, turn various switches on or off and then then that program will be remembered)

So, because the interval write is working, it appears as though the microprocessor system is working, but I can't write to memory. The system is based around a 8048 and the RAM is a 5101. My completely uneducated guess would be the RAM chip as the only function that doesn't seem to work is writing to RAM.

The RAM is easily obtainable. I recently sold my DATA I/O box, so even if I could get the firmware for the 8048, I can't program it. But again that doesn't seem to be the problem.

I'm ok with something like a blown capacitor in a power supply, but computer circuits aren't exacltly my forte.

Any thoughts? I'm thinking maybe the 5101 chip? (Also, ARP's are a bitch to work on the way the PCB's are under the sliders. Also, I'm not sure if hte RAM is socketed or not, as the board faces the wrong way.

I'm somewhat reluctant to go pulling the microprocessor board, just to see if the RAM is socketed, as the Quadra has been extremely tempermental the whole time I've owned it (since 1988) but I'm also fearful of cascading casualties. I did come across a website regarding old video games (which also share the 8048/5101) that stated the 5101 was susceptible to battery leakage/failure. Don't know the context, but I've been pretty remiss in changing the 3AA batteries that power the memory. My completely uneducated guess would be the RAM chip, as it seems the only function not working is writing to RAM. Also, I don't really need the 16 program locations. I am never going to gig with this keyboard, and I am perfectly happy turning on and off whatever section I want when I need it. The only reason I'm concerned is with having something else fail as a result of this failure.
 
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UPDATE:

The RAM chip (and I'm assuming the MPU) are socketed. (I haven't pulled the board, but can see the 5101)

I've located a replacement MPU, so I'm going to replace the RAM chip and see if that is the problem.
 
Is the 8048 a generic part? I heard they had 2K of ROM on-die, which might mean a custom part (I think the TSR-8 is like that). Is there an EPROM on the board somewhere?

Sadly I don't really have much to suggest. All I really know about the Quadra is rumours that they were extremely flakey and difficult to keep going. Unfortunately.
 
The 8048 has its own firmware, which is why I've been hesitant to start monkeying about with the board. But I've done a bit of research and it seems the 5101 RAM is prone to failure. It isn't *that* much to replace and it's socketed.
 
You've probably already seen it, but this site seems to be selling a 5101 replacement that's probably flash-based:
Index Page
 
Thanks, I noticed quite a few 5101's NOS or 5101 adapters with other types of RAM. I bought a couple of RAM's, going to try that out as soon as I secure the 8048 (which is the only part i can't easily replace)
 
Ordered a programmed 8048 from a guy in England. Have RAM on its way as well. Hoping it is the RAM chip (which is socketed.) The 8048 wasn't cheap (dollar vs pound....) but I want the security. The only other thing I could think of is the TTL chips that support the RAM (74LS175 I believe.) RAM is an easy swap, will try that first as soon as they come from Las Vegas....
 
Fundamentally successful! Got some NOS 5101 RAM. Replaced. Getting the board off was tedious, lots of pin connectors. Replacing the RAM solved the problem, and it stores programs. However, somehow, I killed the left interval write switch (which is how the lead synth section knows where to reference its pitch or setup a two note "trill")

however, there are two of these, and I rarely used the right one, and the right one works. However, I've heard these switches were forged in Mount Doom out of genuine Massachusetts unobtanium. Hopefully it was just that mylar switch which died on its own, unrelated to my messing around with the ribbon connector.

Also the ribbon connector for the logic mechanism on the left part of hte keyboard was real real touchy, finally got it seated correctly so that all teh switches work, (it is a damn logic matrix of some sort, but I can't close the connector, so heaven forbid I have to move the thing and it shifts out of place again....)

That ribbon connector is a weak point on this thing. This is an awesome keyboard, but it needs a whole lot of lovin....
 
One final follow up:

The interval write on the lower side works fine now. I needed one extra hand to hold the computer board to properly seat the plastic ribbon connector all the way.

I'm waiting for the programmed 8048 to come as a spare.
 
Blue Jinn said:
I'm waiting for the programmed 8048 to come as a spare.
Click to expand...
How's that work, anyway? Is it the variant with the EPROM, and the guy has programmed it himself? Or is it a NOS one from ARP that was factory-masked?
 
Dunno. It's not a NOS ARP programmed part. I'm guessing it's a clone of a good one. I'm pretty sure that is possible, again based upon some of the websites/blogs/etc. I came across related to Pinball and video games which share a similar architecture, and I don't think the 8048 is protected in any way. I'm planning to keep it as a spare. My particular machine has the EEPROM 8748 not an 8048.

I used to have an older programmer (Data I/O Model 29B) I only used it once for an absurd experiment to put on meg of RAM on an IBM XT. I'm guessing it all worked both ways.
 
A few bits more>

Got some recommendations to replace the 3AA's with a lithium coin. The datasheet for the 5101 indicates it works on as little as 2v.. So that is now on the List of things to do.
 
Got the programmed 8048's (or in this case the EPROM version 8748) from Synth Repair Services of Stoke on Trent, England. The only gear photo on his websites "gallery of repairs" at the moment is of course a Quadra... :-)

Apparently there are/were two versions of the firmware. This are/were two revisions of the Quadra, based on the ARP model numbers. No idea what the differences. The SM is for both model numbers, no difference in schematics etc, that I can tell. I sold my Data I/O 29B a while back, so I don't have any way to extract the firmware and actually look at it...

I'm not going to replace the MPU any time soon though, as I'm a. superstitious, and b. hoping to *finally* do some music this summer...
 
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Hi, Blue Jinn,

Thank you very much for helpful information.

My Quadra is suffered from the same issue. I think it might be happened by the leakage of battery.

Could you tell me how to get the programmed 8048?

Best,
 
This thread should have all teh info you need. If the issue is the same (ie not remembering patch programs) but all the other computer functions work, keyboard scanning etc, then replace the RAM first. Google the RAM and you'll find plenty of NOS suppliers of the 5101 RAM chips. I got mine off Ebay though from a seller in Nevada.
 
Hi Blue Jinn,

Thank you very much for your helpful information.

I have the same issue in my ARP QUADRA.

Could you tell me how I can have the RAM?

Greeting from Tokyo,Japan.

Yoshi
 
Download service manual and schematic here:

Synthfool:Docs:ARP:Quadra

The 5101 RAM chip can be found new old stock from companies that service older (1980s era) video games and pinball machines. I purchased the RAM from Ebay, if you are in Japan, you may want to try and source the RAM locally. Do a search for "5101 RAM" or "NOS 5101 RAM" on Ebay or Google. If other functions are working OK (for example, can you set the interval write?) then it is likely RAM and not the MPU itself.

Also, make sure you change the batteries. I have heard you can use a 3v lithium battery, I have not tried this yet.

Bad alkaline batteries can leave corrsion, so ensure you clean the boards as well. Be aware of static though when you clean.

If you open the Quadra, the microprocessor board is on the top as you are looking at the lid of the machine. The 5101 RAM chip is socketed and located on the left hand side of the board as you are looking at it while the board is still installed. It is Z7 on the schematic. You'll find a board layout on pages 6 and 7 of the service schematics, found in the link above. The IC is clearly marked on the schematic and on the PCB drawing in the service manual. Please review the drawings in the service manual and post any more questions you may have. I used a New Old Stock (NOS) 5101 RAM chip, not one of the adapter parts listed earlier in this thread. I purchased from this Ebay seller, with no problem: http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=280663607829 I don't know if this seller will ship international.

You have to be careful removing the boards, there are multiple pin connectors, and an overlapping connector board. All of these are 30 years old and the microprocessor board attaches to the lid of the machine also via two thin plastic connectors. These must be carefully removed, and carefully reseated or the mylar switches won't work properly.
 
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