JX3P keyboard fixing

After a quick attempt to fix my Midiverb II again (and failing) I pulled the JX3P out again to have an attempt at fixing the dodgy octave.

Thinking that it was possibly the keyboard decoder, I replaced IC45, which took a fair amount of time to do it cleanly with the desoldering vacuum.

JX3P - removing IC45

While I’ve got the board out…

Crinkly JX3P circuit board

not sure I really like the look of these crinkly paths on the back. Anyway onwards.

Changing IC45 made zero difference, so it wasn’t that. And anyway, I could see the signal appearing on the connector on the keyboard. It took me a while to work out what was going on, and it definitely made it easier yanking the keys out.

JX3P keyboard diodes

This is part of the dodgy section of the keyboard, and it looks a lot like my unhappy Poly61M from the same time. The rubbery circular things are pressed down by the keys – inside the dome is a carbon disc that presses down onto the board and completes the circuit.

One side of the switch connects to the top of the diode below it, with the other half connecting to the decoder IC45 via the keyboard connector at the far side. Pressing the switch should make the signal from IC45 appear on the other side of the switch (the top of the diode).

I can’t believe you’ve got this far, but aaaaanyway, the signal wasn’t coming up on the diodes for the broken section.

The soldered track on the far right here should have given the game away

JX3P keyboard connector and track fix

…essentially the track had failed for some reason. Scratching out the soldermask from either side of the break and soldering a wire across it sorted it. It wasn’t actually super-obvious where the break was from just looking at the track, it took me a couple of test scratches to work it out.

There was also one intermittent key which just needed the rubber switches refitting, and that was sorted too.

I still have lots of screws missing (in the JX, that is…), and the transformer hums like an electricity substation, but at least it all works now.

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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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