I did a RAM upgrade for the Prophet 3000 a few years back. Unfortunately, it didn’t work correctly, and I didn’t have the motivation or the time to figure out why. It was strange in that it would fail some tests and pass others.

To give a bit of background, the Prophet 3000 has several custom chips. Two of them, the “I-627” (voice controller) and “I-628” (DMA controller) share control of the sample memory. The I-627 plays back samples and the I-628 transfers samples from SCSI or the main processor to sample memory. The diagnostics let you run memory tests with either the I-627 or I-628 controlling the test. The board I built was passing the I-627 tests but failing the I-628 tests. I figured that the problem was somehow timing related but I decided to shelve the project.

A few months ago a friend purchased a beat-up P3000 that had been in a storage shed for years, and asked me to restore it. After many hours of ultrasonic cleaning, rust removal bath, IC socket replacement, re-capping, and replacing regulators and a few defective parts, it was up and running again. I decided to revisit the memory board issue. I used a logic probe to look at the memory timing and discovered that the I-628 is much more sensitive to timing than the I-627. The memory address and data buses are multiplexed and the address bus itself is multiplexed. Therefore, the 16 lines share three pieces of information: address row, address column, and data. Two other lines, RAS and CAS, go active as these transitions take place. What happens with the I-628 is that the address row and column transitions are too close to the RAS and CAS signals. Memory chips have a “setup time” where the address has to be valid for a certain period (usually a few nanoseconds) before the corresponding RAS or CAS signal activates. The onboard P3000 memory has IC buffers that add a bit of delay for these signals, and my board was lacking those. I had assumed that the buffers were there to reduce the load on the sample memory bus, but it was also adding the necessary delay.

I modified my design with simple logic gates to buffer the RAS, CAS, and memory read and write signals and got a few test boards made by OSH Park. And now it tests perfectly.

I also discovered that certain brands of RAM fail the memory tests due to out of spec timing (this is the RAM that goes in the expansion sockets on the motherboard). Hitachi was OK, the original AT&T RAM was OK, but Mitsubishi would fail testing after a while (due to heating up, I guess).

And finally, none of this would be possible without a new I-627 rev B chip. I made an adapter for the first generation P3000’s with the PGA style I-627 to enable fitting the PLCC package I-627B. The original I-627A couldn’t deal with more that one bank of RAM for some reason. Unfortunately Wine Country seems to have stopped selling the I-627B’s, so at this time the only P3000’s that can be upgraded are the second generation.

To start the new year, the EPS16 SCSi boards, the 5530 replacement modules, and the DI-10 are all back in stock. Use the contact form (not the comments) to get in touch if you’d like one.

I’m going to try and get at least a prototype of the new DSS-1 upgrade finished by June. It’s been a difficult couple of years with work related turmoil and other issues preventing serious progress on any projects. But, so many people are asking for the DSS-1 upgrade that I feel I need to finally produce results!

In recent months I’ve been learning KiCad, which is an open source EDA package available for many platforms. Version 5 has just been released, and it now imports EAGLE projects. EAGLE has been purchased by Autodesk, and they have been rapidly improving and updating the software. The only problem is that it is now a yearly subscription model, and I can’t justify spending $500.00 per year when I don’t do PCB design on a regular basis. EAGLE version 7.70 has served me well up to this point but KiCad is free and also has many of the features of the new Autodesk EAGLE. It doesn’t have an autorouter, but I’ve rarely used one in the past anyway. It does have interactive push and shove routing which I find to be more useful.

I’ve also updated the links section with a few corrections and additions.


Just received the SCSI boards from the manufacturer and they look great. This time, made them ENIG instead of HASL (better quality). And because I got more made this time, the price is now $129.00 instead of $149.00.

Send me an email (via the contact form) and I will send you a PayPal invoice. Make sure your shipping information in PayPal is up to date, and let me know the PayPal email address, and where you are located, so I can calculate shipping.



I’m currently organizing to get another batch of EPS16 SCSI boards made. I’m doing a bigger order this time so I won’t run out as quickly.

I have completely sold out of all the other boards, but will get more made, depending on customer demand. This includes the 5530 clone board and the ASR-10 SCSI and digital input boards.

I had some left over bare boards and parts from the first generation DSS-1 upgrade. It’s been quite a while since I built those, and getting all the pieces together was more work than I thought…the parts are harder to get now, the Xilinx ISE software won’t run properly on Windows 64 bit, I didn’t properly document which versions of the design files should be used, etc. Finally got them finished, though.

Many people have been asking about the new version, and unfortunately I don’t have an answer yet. I do have a large amount of the hardware design done, and getting the last of the original upgrades finished off has put me in the right frame of mind to continue on with the project. Time is the biggest resource that I lack. I’m at work 60 hours a week and unable to do work on outside projects during that time, and those of you with children know how your free time disappears on the weekends.

In the meantime I’ve started a few smaller projects, experiments really, to keep active. One of these is a digital output board, so you can bypass the DAC’s. For those synths and samplers which are mostly digital anyway. I’m going to try modifying a few of my synths and see how it goes. Will it sound better, bypassing the ancient analog sections? I’m going to find out.

Johan Sahlberg has had some ME-16 expansion boards manufactured, based on a design I did that never saw the light of day. If you’re interested, contact him directly at f_l_y_h (at) hotmail.com. He has a very limited quantity available.

Work progresses slowly on the DSS-1 upgrade. However I have almost completed the design for the new processor daughterboard.

I’ll probably end up missing the 2017 self-imposed deadline unless a miracle happens.

Nothing much new to report. School is back and my daily commute to work is 90 minutes again. Combined with the 10 hours per day, six days per week work schedule, guarantees that nothing much will be getting done for a while. The ASR10 SCSI card issue has been resolved. Supplies of the EPS16 SCSI card and DI-10 digital audio interface for the ASR-10 are running low. I’ve added a bunch of new items on the gear for sale page. I’m trying to clear out some of my less used gear.

I’ve contemplated designing a conversion kit for the ASR-10  to go from a VFD to an LCD (purple screen). Looks like they used a device with an external EPROM to emulate the functionality of the old display controller so it’s technically feasible. The only question is whether the newer LCD displays will physically fit in the space. I’d just have to get a hold of a purple screen ASR or at the very least a purple screen ASR display board. Might work with the EPS /16 series as well.

We’re having a hot, muggy summer in LA this year. I’ve been spending more time in the pool than in the workshop. However I have had a bit of time to start preparing my ASR10’s for sale. In doing so, I made an unfortunate, albeit interesting discovery.

I had made a clone of the SCSI board (model SP-3) for the ASR-10. The first batch I did used the same SCSI controller as the original board, an AM33C93 from AMD. For the second batch, I had found some Western Digital WD33C93. The EPS16 SCSI board had used the Western Digital version, so I figured everything would be cool…unfortunately not.

I had done most of the testing on a first-run ASR-10 with a mainboard dated 1992. All the testing with the second batch of SCSI cards was good. However the past week when I was preparing another ASR10, I found some issues. Although it would boot from a SCSI drive, the ‘change storage device’ and ‘copy OS to drive’ would give ‘file operation error’. Long story short, the ASR10 in question had a mainboard dated 1993 which had been redesigned. The newer mainboard did not like the WD33C93, but was happy with the AM33C93. In fact the AMD version worked properly with all revisions.

I did a bit of research and found that the WD versions had several revisions; the latest being 00-08. The chips I used were a mix of 00-04 and 00-06 which were reported to contain various bugs, although I was not able to get the specifics on what was affected. Apparently the AMD version was equivalent, or derived from, the 00-08 version of the WD controller. Perhaps the first generation ASR mainboard was designed to be compatible with the WD controller, and once they switched over to AMD, this compatibility was removed…

So…for anyone who bought the SCSI board with the WD controller (it’s the only square chip and has WD printed on it), I’ll happily replace the board or just the SCSI controller. Contact me and I’ll get it sorted out.