SMR4 kit: 10k marked resistors measuring as 5k?

Finished my control and filter board last night, but it wouldn’t boot.

I’ve found that 6 of the resistors, though with the markings of 10k, are measuring 5k on my multimeter.

I assume this is a manufacturing error and I’ll need to desolder them and acquire some 10ks? Or am I making some mistake?


(I should have tested all the resistors before soldering them onto the board)

You cant measure a resistor in circuit, you will measure the whole resistor network instead (google for Ohms Law and you will understand). A wrong labeled resistor would be the first one i ever saw…
None of these 10ks would keep your machine from booting, so lets just follow the usual trouble shooting process - theres a reason for the order of tests in that procedure :wink:

Did you do the voltage testes and if so what are the readings for the positive and negative rail?

I did the voltage tests at the step described in the instructions, and they were fine.

right so, i’ll assume the resistors are actually ok as a mislabelled resistor seems near impossible from what you are saying.

i’d been connecting to each end of each resistor with the multimeter. I had tested all the other resistors in the same way and had good readings. Thought it was odd that the ‘faulty’ ones were exactly 5k rather than 10k but i guess this was due to their position in the circuit and i’d need to detach them from the board to do the tests properly - which would then show them to be 10k.

I’ll revert to the trouble shooting process. thanks FCD

Your resistors are fine. Imagine putting two 10k resistors in parallel and putting the meter across one of these resistors. You’re actually measuring the resistance of the whole network between the two points and you would read 5k. The meter has no way of “isolating” the probed resistor from the rest of the circuit (unless you cut it!).

> but it wouldn’t boot.

You mean you don’t even see the backlight on the LCD? That’s odd. How much do you have on the +5V rail? Looks like the +5V rail is shorted - maybe there’s a short between two adjacent pins on one of the boards, or an IC inserted backwards?

All good now. Also touched up all solder points which seemed to be the cause of the no boot. now have a live LCD with expected text. Moving on to final spacers and then more testing. Thanks for the help!

got as far as could scroll menu on the lcd, could hear test sound. Then tried to play via midi and no response on the unit. powered off and on - and now the LCD just glows, but no text.

tried adjusting the LCD contrast. It seems the little screw just goes infinitely anticlockwise? Is it meant to eventually stop?


It will not stop, a faint click can be perceived when hitting one of the extremes.

the screen had been working fine so i doubt it was the contrast. i’ll try desolder the lcd…

Screen working again after resoldering trimmer points. Still no midi. Seems way to fix might be detaching the LCD which seems very difficult.

Voltage on pin 6 of the 6N137? (at rest and when there’s a lot of MIDI traffic).

Think I found the problem :

From teh instructions “Finally, add the diode D1, which is polarized. The black ring of the diode goes on the opposite side as the D1 label on the board – it should point towards the MIDI connectors.”

However on my board, v0.8, the D1 is printed on the opposite end of the diode to that intended in the instructions, so I soldered the diode on the wrong way around (ignoring the ‘it should point towards the MIDI connectors’!).

Anyway, I cut off the diode, reversed it and resoldered to some short wires. And I’m now up and working with MIDI.

thanks for all the help.