3/2/2023 0 Comments Marshall jmp 1The customer mentioned that amongst other things, the data entry control on his JMP-1 was skipping, making it difficult to manually select patches and change parameters. I always seem to have a couple of JMP-1s in for service but just before Christmas 2020, I had one that was of particular interest. This where Eclipse conveniently connects to. Simple, eh?!? □ 3-pin Molex connection between data encoder and main PCB. Unless you intend to change the rotary data encoder at the same time, you don't even have to remove the front panel. Unplugging this connector and plugging it into Eclipse and then plugging Eclipse into the socket where the encoder was originally connected, only leaves one wire to be soldered to a filtered +5V supply point and you're done! You don't have to remove the main board and as mentioned, there's only one solder point to make. The data encoder in the JMP-1 is attached to the motherboard via a 3-way Molex connector. This is how Eclipse affects the signal from the JMP-1's data encoder.įundamentally, Eclipse Marshall JMP-1 skipping data encoder fix, is an active bounce eliminator which can be easily fitted between the JMP-1's data encoder and the main PCB and hence, the inputs to the 8031 processor. This is achieved using what are called Schmitt triggers. One hardware approach is to use passive filters, a combination of resistors and capacitors but due to the unpredictable nature of bounce, this approach can also be unreliable and so Eclipse uses the preferred third option which is to delay the reading of the signals coming off the encoder, thereby missing the bounce. RE0 and RE1 off the data encoder, go straight to pins 12 and 13 of the processor with no bounce eliminator circuitry. I have no idea if the firmware of the JMP-1 includes debouncing suffice to say that if it does, then it doesn’t work! A hardware solution is always preferred. What the processor wants to see is kind of ‘underneath’ the spike.įor some crazy reason, Marshall, didn’t incorporate a hardware debounce circuit in the design of the JMP-1. Debouncing can be done in software but generally, designers aren’t keen on this approach. To overcome the problem of bounce on mechanical data encoders, a bounce eliminator (or bounce filter, as it's sometimes referred to) is required to remove the spike, thereby making the signal look more like the regular pulse it's supposed to. Modern data encoders are optical and so there's no physical contact between a wiper and a track and hence, no bouncing. All it wants to see is noughts and ones at nice regular intervals (a pulse). This is called contact bounce and if the data from the encoder is going directly into a processor, then it should come as no surprise that the processor just wouldn’t know what to make of it. When the wiper leaves or comes on to a switch contact, the electrical signal can be quite transient and messy, similar to an electrical mains spike that sometimes occurs when switching lights on and off but obviously not as big. This is a very simplified representation of the inside of a potentiometer (left) with a continuous resistive track and a data encoder (right) with a series of contacts.Īs you may have guessed, this means that there’s a gap between each switch contact (correct) and as the wiper moves, there’s a region of zero contact between the wiper and any switch contact. Unlike a potentiometer which comprises a wiper that's in constant contact with a resistive track, a data encoder is basically a series of switch contacts with the wiper moving from one contact to the other, as the encoder is turned. Hence, I designed the Eclipse Marshall JMP-1 skipping data encoder fix. ![]() ![]() Cleaning (yeah, right) or even replacing the data encoder, doesn’t always resolve the problem. I regularly receive Marshall JMP-1s for service and customers often complain about the skipping or jumping of the data entry control.
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