I´ve had a broken Alesis Midiverb II lying around for quite some time now. Just recently I remembered that I´ve always liked Patch #28, even before I dove into ambient and drone. So I thought now was finally the time to open it up and give it a go, especially since not to long ago I aquired a Midiverb 4 from an old friend and thus had a working 9V AC/AC adaptor again which the Midiverb II also requires.
You´d plug in the power adaptor and nothing would happen, neither visually nor sonically. The unit was basically dead, or so it seemed …
It´s always a good start to make sure that all the supply voltages are there and within range. The Midiverbs rectify internally so I started at the power adaptor plug and made my way through the PSU unit. Power on all paths was present but at very low ratings. I unplugged it again and did some continuity measurements. I found a short circuit between the output and ground of the 7805 regulator. I took it out and found that it measured okay out of circuit so it itself couldn´t be the problem. I still had to replace it because the input leg simply broke with no real force applied,
So there was a short circuit on the 5V supply line. I measured continuity across all capacitors and marked al those that seemed short which I then soldered out. Basically I removed all ripple filter caps of the digital ICs. Subsequently I no longer measured a short circuit across the 7805. It turned out that two of the filter caps had shortened. I replaced those with 470pF that I had left over from the Opra 6 repair and put all the other working ones back in. That was all it needed. Plugged in the adaptor and there it was up and running again.
I noticed that the unit emitted a slight humn and a significant amount of noise when cranked up fully. I then remebered that the device has always been a little noisy. I then found that it might not be a bad idea to check whether the analog circuit could be improved upon. All opamps where LF347 and a little research revealed that the TL074 is compatibel and seemed to have better ratings. So I decided to replace all LF347 with TL074. I used sockets just in case that I where proven wrong and had to reverse it, which didn´t happen. I am quite stisfied with the improvement and really happy to have the unit back in working condition.
If all of a sudden you are getting an error message on your Computer stating that your USB device failed then this is most likely due to worn out capacitors of the power supply.
I successfully got my device working again by replacing the two 1000uF electrolytics. The original ones where causing ripples on the supply voltage which lead to instable USB signals.
Like some other 80´s polysynths with memory, many of today´s Poly-61s suffer from battery leakage. The problem for most owners without knowledge of the technicalities is that the symptoms come on slowly and do not neccessarily hint at memory. While leaking, the battery may still provide enough power to retain memory while starting to damage the PCB area around it. The device starts acting weird up to doing nothing at all soundwise. The symptoms depend a little on how the synth has been stored and therefore how the acid flowes across the board. If you see a Poly-61 on the used market described as ‘functional’ but ‘holding a steady tone’ it´s most likely a battery dammage.
I purchaised such a unit with the risk of not knowing the exact amount of dammage it had taken. But I was determined to make it fully operable again. After all I thought it couldn´t be worse than the Opera-6 fix. Continue reading →
Some older Roland keyboards suffer from a bad choice of material. The metal plates that give weight to the keys are glued in with a red substance that eventually looses its consistency and drips onto the keybed. Roland did offer a replacement for applicable devices, but it appears that they are now out of stock and can therefor no longer provide that service. Affected devices are mainly JD-800 and D-70. Both my units were affected so I had to come up with a solution. Fortunately not much harm has been done yet so I just had to do a little cleaning.
Here is an image where you can see what it looks like when the glue starts to flow
On the next picture you can see the consistency that it takes on. I used a screwdriver to push back or scrape off the red stuff on seriously affected keys.
I then took a hot glue gun and sealed the red glue along the edges. This should prevent it from flowing. At least I haven´t experienced any leakage again since then.
The whole procedure took a good hour and about ten sticks of hot glue as the black keys need a little more filling.