Roland TR-808 repair

An TR-808 on the bench for a repair.

TR-808 not working

TR-808 needs repair.

The ‘start/stop’ as well as the ‘tap’ button only worked from time to time as well as the handclap sound, from which one could only hear a faint ‘reverb’ tail as well as  some continuous noise on the output.

TR-808 Start Stop

TR-808 Start/Stop buttons not working

In order to fix the buttons, I had to unsolder both of them, carefully pried them open with a sharp screwdriver taking care not to damage the housing. Then I cleaned the gold contact on the base of the switch with some Caig ProGold and the black rubber grommet under pushbutton with some water on a clean cloth, trying to rub the surface clean in order to remove all possible dirt, thus allowing a good contact again. Soldered them back in – working.

The clap circuit was a bit more complicated, as it uses a BA662 as VCA, a part which is almost impossible to find nowadays since it was made proprietary for Roland .

BA662 in TR-808 Handclap Circuit

After some measurements in order to check if it was really the OTA which was defective (well, I could have told even without measurements since the chip was steaming hot…) I unsoldered it and started looking for a replacement part.

I chose the easier available BA6110 as a suitable replacement part, although it is not pin to pin compatible.

I had to create a small adapter board in order to rewire the pins to their corresponding location.

TR808 BA662 replacement

BA6110 to BA662 adapter

In case you wonder, I did not have to build a current mirror for the control input of the OTA since the TR-808 clap circuit is already current controlled. If you plan to use this chip as a replacement for the VCA in a TB-303 you would have to build such a current mirror around the control input in order to not change affect the voltage levels of the original control circuit.

The new BA6110 installed on the TR-808 PCB, the two resistors on the right had to be replaced as well since they suffered from the high current load of the defective BA662:

TR-808 BA662 replacement

TR-808 BA662 replacement

Circuit for BA6110 to BA662 adapter:

TR808 BA6110 to BA662 adapter

TR-808 BA6110 to BA662 adapter

And the corresponding board layout:

TR-808 BA662 to BA6110 board

Board layout for BA6110 to BA662 adapter

So, I finished with a fully working TR-808 again, nice crisp handclaps as expected!


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