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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Distorted output from an Akai S950 sampler

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Mmmm, chips. Barely 20 minutes into using my newly-purchased S950, the sound became extremely, digitally-ish distorted. So before I start crying, it’s a good chance to whip the top off the thing and see what we’ve got in the grey box. Mmm, circuit board porn.

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…and it’s a lot busier in here than I expected; the weight of the box (almost 11kg according to the manual) should have been a clue here. But then this thing did come out in 1988 – my (also broken…) E-MU ESI 2000 is virtually empty by comparison.

So you can see the power supply on the left, with a large heatsink. There’s at least two big main circuit boards, the lower one hidden by top one, which I’m guessing is the voice board, because of the eight identical columns of chips, one for each voice. I imagine the main out is on the right-hand side somewhere. Underneath this I imagine we have some sort of CPU board. There’s a large trapdoor underneath for adding two 750KB expansion cards. If your S950 says 512 Kwords on bootup, it’s unexpanded – 1024 Kwords 1536 Kwords means it’s fully expanded to 2.25MB.

I was hoping that there was some sort of loose connection rather than a blown opamp or power supply problem, which I’d be rubbish at fixing and tricky to track down. There are wires connecting the circuitboard to the audio out board – waggling and pushing the wires down into the socket the wires in this area (top-right as you look at the picture above) fixed the problem.

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So I’ve not had a great chance to play around with it, but here’s a not-particularly indicative scratchy loop of a TR-606 and Boss handclap, with heavy spring reverb, sampled at 5KHz, sat next to an MS20 bassline recorded straight into Ableton Live.

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