Glitching Wasp keyboard fix

edp wasp inside

Bastard thing. It mostly works now, except when it doesn’t.

Ages ago, after moving house, I got my Wasp out to have a go at MIDI-fying it, and found that it would glitch when holding a note, as if it was flickering quickly between the held note and one much lower down.

Since then the Jasper clone was announced and released, I’ve got mine up and running in the last week, and that seems to work ok (although the VCA envelope sustain gets louder as a key is held down, which isn’t quite right). But the keyboard triggers absolutely perfectly, so it gives me a chance to compare it to my old Wasp.

Jasper (Wasp clone) all done bar the shouting

I noticed irregular pulses on the 4013 at IC44 on both Q and Qbar (labelled NOTE_READ and VCA_ENV_TRIG on the helpfully labelled Jasper schematic). I didn’t trust the Q-to-reset link, so I recreated that on a breadboard and linked to it, still the same. Checked the connections, my soldering might have been wonky – all OK. I replaced the CD4013 with a HCF, supposedly has Schmitt trigger inputs, so could be more forgiving of noisy inputs. Nope.

After much fretting all I had left was to strap a ceramic 0.1uF capaacitor across ground and +5V on IC44, and… it was much less glitchy. I added a couple more (fairly randomly) in the keyboard circuit, and then the glitches stopped.

And only then did I have a look at the 5V line on one of the non-decoupled ICs:

EDP Wasp - noise on the 5V rail

…which doesn’t look like it would much help. The Wasp uses a couple of NE555 timers at heart of the oscillators, and they have a tendency to smash the power rail. Only as far as I could tell the glitch wasn’t at its loudest next to the 555s, so I suspected something else.

Now I’ve put it all back together, I realise that 3.36µs works out to about 297KHz, which is in the same ballpark as the frequency of the master oscillator, which is supposed to run at 250KHz. Next time I open it up I’d be tempted to put a capacitor across 5V and ground on IC11 and see if that quietens it down.

Anyway with the glitch gone, I dared to start celebrating, and then found a different, intermittent problem – G and G# would play the notes B and C. Pressing the keyboard slightly harder seemed to bring the problem on, so it seem likely it was a dodgy solder joint, and I tracked it down to a dodgy connection between IC31 and IC30 – reflowing the joint on IC31 fixed it.

Very occasionally still F# will play a slightly inbetween lower note, but I’ve spent way too long staring at this as it is – I’m calling it done for now.

As a postscript, if you have a knackered or badly behaving Wasp, I had a look around for some help on fixing the keyboard and there was some interesting stuff in this post and comments on the Clacktronics post on the Wasp, but that’s about it. Now there’s a new generation of Wasps springing up in the form of the Jasper clone, the Muffwiggler DIY section might throw up some new help.

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JX3P MIDI in fixing

I bought a rough old JX3P a few years back for not much.

programmable preset polyphonic

It sounds surprisingly nice – whoever had it before me had programmed in some pleasantly woozy sounding patches into bank C and D.

The chap I bought it off was upfront about the MIDI in not working, and I naïvely thought they might have just not checked the switch that selects between the PG200 programmer or MIDI in.

Haha, no.

Tried the usual swearing, different cables, different sequencers, different swearing, nothing.

Let’s have a look inside, there’s a few things wrong.

Battered JX3P internal overview

Look at this transformer! It hums like a bastard, hence this odd arrangement to try and dampen it.

Wonky JX3P transformer

Needs replacing really, but it works OK.

Something heavy must have fallen on it at some stage and smashed into the last button on switch panel, it’s still a bit wonky looking.

Wonky 16 button

Here’s some wiring to fix the cracked part of the panel switch board; good effort previous owner. The “16” switch LED nearest this calamity doesn’t work any more but on a quick check, the connections beep out fine.

JX3P switchboard extra wiring

On holding an LED to the two contacts on the back of the board it happily burst into life. Closer inspection revealed that the impact had just pushed the LED pin down and popped the joint, you can just about see it here.

16 button LED dodgy joint

Reflowing sorted it.

Let’s play the keyboard, oh dear. Well it mostly works, some are a bit intermittent, but keys 17 – 24 don’t do anything despite heavy bashing. I’m pretty sure this is a recent problem.

Usually I’d assume that the key contacts are dusty (hello Poly61 and Polysix), but it’s a bit suspicious that exactly eight keys don’t work. It turns out that the keys are grouped in eights for scanning, so I’m suspecting either wiring or the demultiplexer IC45.

But I’m not looking at all that now, I’ll do nothing else this weekend otherwise.

Here’s the DIN board.

JX3P broken DIN board

Looks alright. Let’s switch the switch a bit, my Poly61M has godawful switches. Nope, nothing.

The optocoupler is the first thing that the MIDI connector hits, so maybe that got fried. I bought a replacement PC900 then thought should really test it rather than just blindly replace it.

As far as I could tell, I was getting a signal on the other side (pin 4). Booo. Here’s the schematic for the DIN board.

JX3P DIN board schematic

The switch for MIDI enabling is grounded for when switched to memory protect and programmer, and is unconnected when set to MIDI in – that line (RX MODE) is then pulled up by the 5V line through the 10K resistor at R5 – so high = enabled. The 10K resistor was definitely getting 5V, but the other side of it read as 0V, whether or not the switch was set to MIDI in.

Having temporarily chopped the jumpers at W4 and W5 to make sure nothing was pulling it down further down the line, all that was left was the 74LS00.

For some reason I’d bought a couple of these eight years ago – no idea why – so here’s the bosted one:

Duff 74LS00

…replaced it with a socket and the new one

JX3P DIN fixed

and now it works!

Score one for methodical troubleshooting rather than just blindly swapping stuff (which is never the answer, really).

I lashed up a slightly ropey CV to MIDI converter to play the JX from my MC-4, and then belatedly realised that it’s not possible to edit the synth from the front panel while it’s accepting MIDI input. Think maybe the Kiwi3P upgrade (or more likely the Organix MIDI expansion, given the cost of the Kiwi3P) might be on the horizon, it’s a nice sounding synth.

Done for now, anyway – although I’ll come back to the keyboard soon. Ish.

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Fixing the Wasp

After a month or so of working hard on some other stuff I went mad and bought an advertised-as-working EDP Wasp off eBay for, er, well, some money. A bit more than I’d like, but nowhere near as much as some people are asking. It arrived in a reasonable sort of state – there’s a hairline crack through one corner and one of the screw holes is also cracked a bit, and a couple of the pot shafts aren’t 100% perpendicular to the board, but well apart from all that.

The way it’s built with the shit plastic front and single board construction reminds me of a shoddier Pro-One, although it doesn’t sound like the American synth. On the plus side I love the retro-futuristic Microgramma (or Eurostile?), and Electronic Dream Plant is the best company name ever, really. Here’s a picture of the inside as I got it:

Wasp PCB - front

and round the back:

Wasp PCB back

And it sounds great. Even just droning a single note with the filter being opened and closed slowly is really satisfying, but there were a few things that weren’t quite right. The bottom key didn’t work (as mentioned in the auction), the VCA envelope was stuck on repeat, and some of the keys played the same note as the one before.

The key not playing was just down to a break in the track underneath one of the 4016s attached to the keyboard, which had been kind-of-not-really fixed by a previous owner.

dodgy fixed not fixed 4016

Suspicious looking 4016

The always-on-repeat VCA was just the wire from the switch on the rotary pot coming loose.

The keyboard problem was trickier to nail down. The service manual offers up suggestions of how to check the state of the keyboard encoding at a couple of places. I found that the binary code produced by the 40174 flip flop which holds the state of the keyboard was fine apart from the least significant bit, which was generally only getting up to 1.38v, apart from two notes where it hit 4.8v.

I then spent about two weeks (I’m not kidding) of evenings trying to work out what was going on. By the end of this I’d replaced most of the >30 year old ICs in the keyboard section. The Wasp has a double sided PCB but the traces aren’t connected through the board, so you need to solder on both sides, which is a horror. It’s really easy to lift tracks. The best way I found to remove the chips was to clip the legs close to the IC body, and then use a soldering iron and solder sucker to take out the remaining legs. If I clipped too close to the board there was a danger of lifting the pad and track.

Legs clipped and IC chopped out

After removing the chip I repaired any tracks that need fixing and put in sockets, gingerly soldering any pins on top first. It helped to leave a bit of solder on the pads for this.

Installing a socket

Installing a socket

Then I tested the connections to make sure I hadn’t created any solder bridges and to check there was continuity between the socket and the track. After replacing one chip I found I’d lost an entire octave, which after some head scratching I worked it this because of a pin not connected properly. On continuity testing it seemed fine, but that was because I was pushing down on the socket and temporarily making the connection…

The 78L05 was only getting up to 4.8v, so I replaced that as well, more out of hope than anything. I started to wonder if the same note on two keys thing was some sort of timing issue, so out came the oscilloscope, and everything seemed fine.

The breakthrough was lifting the leg of pin 2 on the IC30 and seeing that it did get up to 5v on every other key when it wasn’t connected to anything else. At the other end is (at IC27) was a 4019 which had been replaced by a previous owner, and looking at the tracks on the back of the PCB, I could see they were pretty close together at that point, and there was a short. Fffffffffff.

Here’s an exciting picture of the tracks half-way through desoldering, after I’d cleaned up the solder bridge – you can see how close the tracks are to each other:

IC27 tracks really close together

I’d already chopped the legs of the 4019 so I replaced it, cleaned the solder off, and… it worked.

Two weeks of head scratching, and the problem was down to a previous owners’ fix. Lesson learned, really. I’d suspected that chip because of the slightly dodgy top soldering, but all the continuity checks had worked out ok. I knew shotgun replacement of the keyboard ICs was probably not going to help, but I couldn’t see what else to do. Either way, at least those ICs are now fresh and socketed, they should last a good few years.

One minor wrinkle was that I found for the keyboard clock at IC35, that only certain 4069s had enough oomph to trigger the 4013 at IC44 – only an original RCA one, in this case.

Other than the circuit board being a pain, being a single board the Wasp is easy to work on, and it helps that all the ICs are common-or-garden CMOS. Laurie Biddulph of Elby Designs redrew the schematic for the Wasp, and as far as the keyboard section goes, it seems to be correct. There’s also the original service manual and schematic available from Derek Revell’s site.

There’s been lots written about the Wasp on Analogue Heaven over the years (sample subject line: “how do you plug a wasp into a spider?”). One thing I spotted that was possibly useful was Jürgen Haible noting that the LM386 power amp runs directly from the 9v DC input – which is probably the reason mine hums loudly when run from one adaptor, but hisses from another.

I made a video of me fiddling badly with the fixed-up Wasp just to show roughly what it sounds like, reminiscent to me of “On the wires of our nerves”-era Add N To (X). The glide is nice, with the pitch of the two oscillators rising and falling at slightly different rates.

I tried to edit some of the dull bits out, honest.

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