Tag Archives: Oberheim DPX-1

Oberheim DPX-1, Sampler

Oberheim DPX-1 alive

Short resume:

  1. I bought an Oberheim DPX-1 from on eBay
  2. The DPX-1 arrived all dented and wouldn’t start
  3. I was refunded (good seller) and bought another one on a trip to Stockholm
  4. I suspected the CPU since one pin was missing. I ordered a new one.
  5. I replaced the CPU and thought the DPX-1 was working.

Then after a few uses it went all bananas again. At this point I still suspected some kind of “software error” because of some faulty CPU or memory.  I disconnected everything, part by part. Still didn’t work. Then I disconnected the lower main board (the DPX-1 has two main boards). The upper board contains the CPU, memory and midi. The lower board contains all audio specific stuff like filters and outputs. As soon as I disconnected the power to the lower board, the DPX-1 booted perfectly. Quite fun that the upper board can work without the lower one powered up.

Anyway, as soon as I connected the lower board again the DPX-1 wouldn’t start. If I booted without the lower board and then connected it, the DPX-1 would hang. So there was something fishy about the lower board. I measured all voltages and they were stable.

So I disconnected the power to the 8-output and cd-rom expansion card and the DPX-1 booted just fine. At this point I was very happy, but that didn’t last long since I had no output. Nothing but very low distorted audio came out of the original single output.

Next thing to try was to remove the expansion card and then I discovered that the cable going from the lower board to the expansion had to be connected to a connector (J8) on the main board below the expansion card. So now there’s a big hole in the back of the DPX-1 – but I can live with that. I don’t think the 8-output expansion is usable anyway. The cd-rom is very rare and only reads cds that also are very rare. The eight outputs work the same way as on the Emax. Each voice has its own output, so every time you hit a key that sample is heard in the next free output. Eight voices = eight outputs. I’ve heard that there are some EII disks with drumkits and stuff that actually maps one particular sample to use one particular output, but I haven’t found one yet.

Oberheim DPX-1, Sampler

Oberheim DPX-1 CPU problem?

In early March this year I bought an Oberheim DPX-1 on eBay. This example had the latest OS and the rare 8 output expander plus a brand new PSU! Unfortunately it was probably dropped on the ground on the journey from the US to Sweden. I was refunded but got to keep it since the buyer wasn’t interested in paying the shipping back to the US.

This night I opened the DPX up to try and find any clue of what was wrong. Not being an electronics expert, I tried usual of way of troubleshooting, namely removing part by part and see if anything made a difference.

The error could simply be described as the DPX not booting. When it’s powered on it immediately shows a strange character in the LCD display and then lits the MIDI CHANNEL, DATA DUMP and ERROR leds. See the video below day I shot when it arrived.

What I did tonight was:

  1. I started to remove the floppy cables and power cables. No difference, Same error.
  2. I removed the cable to the expansion board. No difference, same error.
  3. I removed the OS chips and doing that on a working unit would most probably generate an error. But no difference, same error.
  4. I removed the CPU, and without the CPU it’s certainly guaranteed that nothing should work, but no difference, same error.

However, removing the CPU, the most important part in a digital instrument, and not getting any other error points to the fact that the CPU might be the problem. I also remember that when I looked at DPX the last time when it arrived broken, the CPU had popped out. What I also noticed now was that one pin of the 64 pins were missing.

CPU is missing pin 1, also known as 'D4'. The CPU will certainly not run at all without this according to a forum member with lot's of 68k experience.
CPU is missing pin 1, also known as ‘D4’. The CPU will certainly not run at all without this according to a forum member with lot’s of 68k experience.

The CPU is a Motorola MC68000P10, a version of the in the 80’s widely used 68k family. I looked it up in the data sheet, and the pin is number pin number 1, named ‘D4’. I asked in the 99musik forum, and someone replied that the CPU most definitely can’t start without D4.

I took a look at some photos taken when the DPX arrived, and in those photos the pin is actually there. However, it could have been very loose then, just waiting to fall off. I’ve looked for the pin in the DPX, but I guess it’s like looking for a pin in a haystack.

I found a Chinese seller on eBay that sells  Motorola MC68000P10s for $8 including shipping to Sweden, I’ll order one of these within the next days and hope that it’ll bring the DPX-1 back to life again. To be continued…

Oberheim DPX-1, Sampler

Oberheim DPX-1 arrived all dented

I just got the DPX-1 I ordered from eBay, unfortunately in a non working state. The front panel is dented, so someone has probably dropped it during transport. I contacted the seller who had just refurbished it and replaced the PSU. He wasn’t very happy to hear the news and offered me a refund.

If I want my $100 custom fees back I had to send it back. However, the transport to the US cost $150. So I decided to keep it and maybe try to repair it someday. Or use it for parts. Now I’ll have to find another one, they’re not too common.

By the way, I opened the DPX-1 and saw that the CPU was loose. Someone must have dropped it really hard. I put the CPU back in its socket, but the DPX-1 still wouldn’t start.