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SEQ V4 Wilba panel LED troubleshooting


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Hello,

 

I soldered the LEDs on a SEQ V4 panel and some of them keep glowing dim when they should be off and one is always glowing very bright. I checked for shorts but couldn't find anything. Then I changed the 74HC595s but I have still the same effect. Debugging is really difficult since I can always measure a voltage between the pins of the LEDs.

 

The config file is is a copy from here: http://svnmios.midibox.org/filedetails.php?repname=svn.mios32&path=%2Ftrunk%2Fapps%2Fsequencers%2Fmidibox_seq_v4%2Fhwcfg%2Fwilba%2FMBSEQ_HW.V4

 

According to Wilba's schematic all of the missbehaving LEDs share a connection to Out14 but I could no find a shortcut between this line and other connections on the board.

http://midibox.org/forums/index.php?app=core&module=attach&section=attach&attach_id=8731

 

The Track and Track Group LEDs are less bright if I switch on the step LEDs.

 

The power source I'm using is a Meanwell RTP-60B with 100kHz switching frequency connected to J2 and on Core STM32. Might there probably an issue with the multiplexing frequency or do you have an idea what could be the root cause? I'm quiet lost and don't know how I can effectively troubleshoot this issue.

 

Seq_v4_panel_LED_issue.png

 

Martin

 

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The power supply is plenty and the switching frequency will not affect the problem.

 

Double-check all soldering joints at the shift register ICs. I guess you have forgotten one, hence there is a floating voltage on some LEDs which causes your problem. A hi-res picture of the underside might help spotting the problem (but this board is large).

 

Edit: Oh, and also check orientation of the resistor networks (RNs)!

Edited by ilmenator
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Thanks a lot for the hints.

 

Today I resoldered the 2 74HC595 today but there is no difference. The orientation of the resistor networks is correct andI think they are in line to read encoders and buttons which is working fine.

 

There is a resistance of 43 kOhm between the QA-QH outputs and the ground connector of the 595 shiftregister, is this normal or shall I look look for shorts?

 

I can also measure a resistance between the outputs of the shifregister 1 and 2 (Out vs DOUT) but these are serveral MOhm, so I don't think this is the root cause of the problem.

.

Is there a good methology to track down the root cause?

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  • 1 month later...
I added a note about LED 31 orientation (twice + bold text) to the SEQ construction guide in the wiki.

Can some post a link to this construction guide in the wiki, I can't seem to find it. I can find the wilba one, but it does not contain the reference to L31.

 

George

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