s950 screen replacement

Saturday afternoon, got a couple of hours, let’s change the screen in my S950.

Here’s the problem – backlight really dim in the late afternoon light. Even with the curtains drawn it’s hard to get a photo with the reflections. If anything this makes it look more readable than it was.

Dim looking screen on Akai S950

Let’s take it to bits.

Front panel removed from S950 to reveal buttons and original screen

I’m using the (slightly confusing) instructions from the Gearslutz Pimp my S950 thread. I bought a 40×2 display from buydisplay via Ebay – this is the one:

Stock photo of replacement display

The original screen has a 14-pin data/power connection on the left-hand side, and the backlight power connection on the right-hand side here:

Close-up of power connection on original screen

I was just interested to see what kind of voltage was appearing here, but it was hard to measure – didn’t seem to be getting anything much, maybe half-a-volt? Partly I suspected that screen is probably fine, but the inverter is stuffed – here it is, lurking in-place behind the front panel:

Power inverter for original screen - probably knackered

The connection on the left is the 5V and 0V connection from the panel – this is what we’ll use to provide the power for the backlight on the new display. The data and power connection for the display uses the bottom 14 pins on the connection, with the 15th and 16th pin taking 5V and ground respectively for the backlight.

As Don suggested in the thread, I connected a 1K pot (albeit linear, it’s all I had going spare) in series with the 5V connection to control the backlight – I nudged it down a bit from the maximum, and it’s probably a bit too bright still but it’s readable.

It took a bit of finagling to get the screen in place – it has to go behind the screw holes because the screen is thicker than the old one. The screws had to go in from the back, which was a bit of a faff.

New screen in place

Here it is with the front panel on:

S950 with front panel back on, screen glowing brightly

Looking loads better. Shame about the scratch through the screen, though not much I can do about that. It was only 75 quid when I bought it (including a massive box of discs) so I can’t complain really.

While I had it open I took some photos of the insides. Easy to see the eight voices on the top board.

View of inside S950 from the top

Getting a bit closer – loads of regulators attached to that chunky heatsink:

Top of power supply

Towards the back on the left we’ve got the power inlet, transformer and the MIDI board – PC900V opto represent.

Transformer and MIDI connection

And there’s this bit, caused me some trouble last time.

Jack board output and PCB

It’s all back together now and happily propping up a bunch of other relics.

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wiring horror, again

I make it hard for myself. I’ve spent a week or so of evenings soldering wires and still the PCBs aren’t even attached yet. Pfft. I’ll get there.

Dig the towel tho, it’s a classic.

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poly61m deathsmell fix

I’d been working on a track and moved a bunch of stuff around, including my battered Poly61M. After recording I turned everything off for the night. And mistakenly left the Korg on.

I woke up at about 3am thinking “what’s that godawful smell?”

Dead Poly61m safety capacitor on PSU board

Yeah, that looks wrong doesn’t it?

Mmmm, 30-plus years of dust. In the middle we have a bulging Rifa 33nF paper capacitor. It doesn’t smell very nice.

The synth still works, but worryingly the power switch doesn’t actually turn it off any more, so the capacitor has failed short.

I found the recommended replacement according to the Rifa datasheet – here’s the bottom of the old burned-up one on the left and the new one on the right.

Poly61M burned capacitor

…and now it works fine again: boring fix, sorry everyone.

Here are some random photos of the inside. I had to take the keyboard out to get the power supply board out, gahhh

Poly61M PSU board

Here’s the main voice board, socketed SSM2056 and all

Poly61M main board

And this is probably the main processor board – there’s another board wonkily attached for MIDI on the left which I cleverly didn’t get a photo of.

Poly61M processor board

Yes, the 80s:

Poly61M hot pink

The electrolytic capacitors in the power supply could probably do with replacing – as could the tactile switches on the front panel – but that’s a job for another day.

Oh and the keyboard barely works as well, which is standard with these. I’ve been in it before to try and fix it but they always die again, it’s one of those inherently shit designs. Good thing it’s the M version and I can control it externally.

I managed to threaten a few keys into action by banging seven bells out of it – here’s me absent-mindedly stepping through some presets and CLICK-CLICK-CLICKING the half-dead buttons.

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