Our patient this time is a Roland SH-32 synth module. It’s a very powerful desktop unit, with a really sweet sound and a great user interface based almost entirely on sliders and knobs. There are a lot of these floating around. If find one for a good price, grab it and start to experiment with the dual oscillator voices and 4 part multitimbral capabilities. I particularly like the analog feel you can dial into the modulations and oscillators, which is really the introduction of minute uncertainties and random variations, as happened naturally in the old pre-digital machines. And although it was originally marketed to the groovebox gang I believe, I find it a compelling spacey electronica unit.
At first, this unit appears indestructible. It’s encased in solid metal. However it has a structural weakness that is a byproduct of its design, and I will elaborate later when we get to it in the teardown. The symptom, though, is that one or more rotary pots are very loose and either send erratic signals or none at all.
The big knobs tend to feel a bit sloppy anyway, even when working properly. This appears to be a quality compromise to keep costs down through the use of mediocre plastic pots and shafts. The sliders, on the other hand, are firm and positive in operation. However, they do not have sleeves so their guts are always exposed to dust and dirt through the slider slot.
So this particular unit was an eBay bargain, which arrived carefully packed and in great cosmetic condition, complete with original wall wart and coil-bound manual. On initial power-up it looked and sounded great. However, the Rate knob was very loose and wobbly and in manual operation was operating only sporadically. If the shaft was pushed from side to side/up and down, random jumpy values were transmitted. Connection problems of some kind.
Removing the knob reveals little except further evidence that the shaft and pots are cheap, with no tightening collar. We will have to tear this down to get a closer look at the problem.
The case is in two pieces: a bottom/sides plate in plain black with pads on the bottom, and a thicker metal case with all the working parts, input output ports, and all the graphics. Hopefully there will be no surprises , like spring loaded parts flying out, when we open this up!
Nope, its very straightforward. The bottom plate comes off easily, revealing the circuit boards inside. Looking down at the unit, which is resting on its control panel, we see there is nothing inside the case except two printed circuit boards. The installation is very neat as seen below.
We still can’t see what’s going on with the pot, so the smaller daughterboard has to be moved out of the way. It is attached to the motherboard by two grey ribbon connecters, a thick one and a much thinner one. Peeking between the boards with a flashlight is encouraging, as there doesn’t seem to be anything else connecting the boards, except the two mounting screws.
The broad ribbon connector responds to careful even pressure and comes loose. The other connector does not, but it doesn’t need to as it turns out, so just leave it alone. Remove the mounting screws. The daughterboard is now free to be flipped to the left.
Now we are looking at the bottom of the motherboard, and we still can’t see what’s going on with the control interface/component side of it. It’s going to have to come out too. That means all the screws associated with the I/Os will have to come out, and all the slider caps and some of the knobs have to be popped off.
This board is very solidly attached. There are EIGHTEEN hold-down screws to be removed. Impressive, and it makes for a very solid base for the working bits, which are soon to be revealed....as the main board is gently lifted up and out:
Aha. In the style of a laptop computer, all the ins and outs and moving controls are soldered directly to the board. Its elegant and cost efficient, but as with the laptop computer design, the flaw is that any mechanical shock to a control surface , a power input, or a midi or audio connection could easily break the solder joint.
That’s exactly what has happened here. The pot in question is three pronged and with a magnifying lens, we can see that the solder joints have fractured, probably as the result of downward pressure on the control knob. It also looks to me like some of these solder joints might have been a bit cold in the first place, although the dull sheen might be due to some special mixed used when the robots produced the populated boards.
The only way to fix this is a fairly tricky soldering job. It’s a very small component as you can see. There are three leads and they are very very close together. A sloppy or bulky solder will short them out for sure.
Use a hot iron to minimize the time you will be in there and it you have a good solder sucker, clean up the old solder quickly. Hit the joint very precisely and lightly, with just a touch of fresh stuff but not a flow...you don’t have room for the usual shiny gumdrop.
(BTW, this very thing killed one of my Dell laptops. The DC input was banged and the receptacle popped off the board. At that time I couldn’t use a soldering iron and took the dealers word that it couldn’t be fixed. I bet I could fix it now.)
While you have this apart, you might as well do some preventative maintenance. As I mentioned before, the slider slots do not have skirts, so there s lost of access for dust and grime. There’s a lot of crap in these channels, which will someday start interfering with smooth operation, and spraying in pot cleaner will only gum up the works worse. I removed an amazing amount of junk with q-tips. In this picture, you can see the difference between the slider channels I’ve cleaned, on the left, and the rest.
Also Ii see all the pot shafts have collected junk, so give them a superficial cleaning with eyeglass lense cleaner cloth. Don’t get too aggressive here, because these pots seem to be treated with a lubrication gunk you want to leave in place.
Power up...and...it works!!
But oh no! While the “Rate” knob is now working perfectly, I discover that the “Modulation” knob is suffering from the same problem! Arg... I’m pretty sure I can fix it the same way but that teardown took up half my evening!
The good news here folks, is that knowing what you know now, you don’t have to remove the motherboard at all. You can access the bottom of it and do your re-solder in ten minutes flat. Flip the unit over and remove the bottom plate. Detach the wide ribbon connector, remove the two daughterboard screws, and flip it out of the way, and there you are. A wiggle of the offending knob confirms the issue, and a few careful minutes with the iron fixes it.
The classic Roland SH-32 lives to roar again!!
Oh, one thing that I forgot to mention. When you are doing this kind of delicate work, with the hot soldering irons and the scores of tiny loose parts and all that stuff, be sure to LOCK YOUR CAT OUT OF THE ROOM.