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Burnt pcb holes trying to replace encoder


Echopraxia

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I've been successful a few times replacing encoders on some of my hardware but fudged on the last one. :(

It happened with an E-MU MP-7 and unfortunately it is the one encoder that is crucially important!

I broke the middle pin trace by melting the pcb a little. So I scraped off some of the mask where the data line is which is going to a mini resistor and made a joint with cut resistor leads. The only problem is it still does not work :(

I can't find the encoder pin out right now but looking from top down with the knob at the top, the left pin does not seem to go anywhere, the middle pin goes to the resistor and the right pin goes to ??? I see a data line but it goes to a empty tiny pad hole. I am afraid this might be a multi layer board.

What would be the best way to handle this now? Should I run wires from the encoder to the board or possibly retrace the board (can this be done)?

I can't find a service manual for the MP-7 but I will take some pictures of the board when I get a chance.

And just to clarify, I took the old glitchy encoder out and put a new different one in (same specs 24 endents but longer knob shaft (ones used on ensoniq gear)) So when that encoder did not work I put the old one back on and it does not work at all now either :( I did also open up the dirty encoder and cleaned it out before putting it back in. Could this have damaged the old encoder? I was gentle :) Just trying to figure out if I screwed the pcb or possibly screwed up the old encoder by opening it up and cleaning it.

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So first picture shows the small resistor that the middle pin is going to.

2nd pic is the underside.

3rd pic shows the thickness of the board (is it multilayer?)

And the last two are top side.

I may need to take off the front panel to fix this now. Can you confirm that the left side pin (looking from topside) is not connected to anything? o me it looks like only the middle pin (to the resistor) and the right side pin which goes ??? on the underside.

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Ugly...

Anyways, I would not assume that the left side pin is not connected - that would not make sense, we all know how rotary encoders work, after all ;-). Also, it does not make sense to use multi-layer boards for something that low-complexity. There must be a track on the upper side of the board, but under the encoder. Remove the frontpanel, then you should be able to see it. The "empty tiny pad hole" is just a via, where the track goes from top to bottom layer.

Once you have removed the front panel, measure if there is continuity between each leg of the encoder and the nearest component (e.g. resistor) or via. If this is the case, your encoder might be busted. If not, you will have to solder again.

Good luck!

PS: This is a very good example why one should not go with the minimum trace width the board house offers, when designing a PCB. This wouldn't have happened if EMU had chosen to use wider tracks...

Edited by ilmenator
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Judging by the amount of traces on the top layer it seems rather unlikely that this is a multi-layer board, then again it's mass-produced with lotsa smd... Either way, all 3 pins of an encoder need to be connected for it to work. 2 data lines and one ground or pullup line will be needed.

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I cannot be certain about the pinout unfortunately. The encoder that was in the unit was stock but I tried replacing it with the same modelencoder that works with the ASR-X. I tried it because everything ensoniq turned to emu around that time. Here are some more pics with the panel removed.

The ones with yellow circles are making me think this is possibly a multilayer board. I hope I am wrong.

I believe the resistor and the middle pin are connected but the right pin (when looking top down) even with via hole on underside does not go anywhere. The left pin does not seem to go anywhere either. Multilayer???

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I cannot be certain about the pinout unfortunately. The encoder that was in the unit was stock but I tried replacing it with the same modelencoder that works with the ASR-X.

That might well be your problem. The one encoder that was in there originally should bear some model name or number. With that you could identify pin-out and look for alternatives.

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That might well be your problem. The one encoder that was in there originally should bear some model name or number. With that you could identify pin-out and look for alternatives.

I went and gave a closer look at both different encoders and sure enough they are both Alpha brand. The only difference I can tell is the factory installed encoder does not have any numbers or letters to indicate what model it is and the knob shaft is a few mm shorter. I think I will email the eprelectronics guy who sells replacement encoders for the mp-7. Maybe I can show him the specs of the new one and tell me if it should be compatible.

I am going to test it with a multimeter tonight.

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...the factory installed encoder does not have any numbers or letters to indicate what model it is...

Oh boy, it seems that E-MU went so cheap in their final days they could not even afford proper encoders (or proper markings on them) by then. On my ESIs and E-5000 they used proper Bourns encoders, but that was a few years before the MP-7 came out. I'm not saying that the Bourns encoders were of high quality, but at least they were easy to identify and replace.

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Well some good news. The ensoniq guy told me that his encoder he sells is electronically compatible with an asr-x. Which should mean that this encoder that I have that works in the asr-x will work in the mp-7. I attached another picture of my progress. maybe someone can chime in as to why I am getting the results that I am getting. Looking top down The right pin is getting voltages of Neg -4.9 constant (without moving the encoder) when black tip of multimeter is at either one of two resistors. And it is positive when switched with the red tip.

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It looks like right pin is the ground/common pin and middle and left are the data lines, which are pulled up via those resistors.

May I suggest you try to pry open the old and new encoders to check their pinouts?

Ok I checked both encoders by opening them up attached is the picture. On the left is the original one and on the right is the replacement. They look mechanically the same. Can you confirm this? if they are the same does this mean that I might have fried a resistor or something else? My last check for continuity just confused me more. What parts could I have possibly damaged when running my hot iron on the traces?

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POIDH! :whistle:

What parts could I have possibly damaged when running my hot iron on the traces?

The traces :rolleyes:

Or maybe you accidently connected the datalines to ground...

Could you also take a picture of the pcb, which shows the whole area around the encoder?

I will mark points on it, to check for continuity, if you do...

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They look the same to me. If you haven't assembled them yet, you could check if those contacts inside are connected to the same pins on both encoders.

The schem confirms: The pin, i marked yellow in the pic must go to ground

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I took the metal base off of the encoders so i was left the white plastic piece that is attached to the pins. I can't tell what pin goes where. I attached pictures if that helps. Where you asking me to do something different? Also is the middle pin for rotating the encoder left or right??? Taking another look at the schem it looks pretty easy. I think i just need to find a suitable place for the ground pin. Any ideas? The other two I think I will just runs wires from the middle and right encoder pins to the resistors right? I think I'll try to fix wires to the encoder first before soldering anything down :)

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Edited by Echopraxia
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