# Ms20 Vcf not working **URL:** \ **Category:** KOSMO MODULES\ **Created:** [June 17, 2022, 9:38am UTC](https://lookmumnocomputer.discourse.group/t/ms20-vcf-not-working/5167 "2022-06-17T09:38:57Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![hansun](https://avatars.discourse-cdn.com/v4/letter/h/bc8723/32.png) [@hansun](https://lookmumnocomputer.discourse.group/u/hansun)\ **Post date:** [June 17, 2022, 9:38am UTC](https://lookmumnocomputer.discourse.group/t/ms20-vcf-not-working/5167/1 "2022-06-17T09:38:57Z")
Hello! I’m new to this discourse thing, I couldn’t find any thread so here I am. I finished the ms20 Vcf late last night, when I plugged it in the whole modular stopped working, and the led’s on the psu went dim. When I unplugged the Vcf, the other stuff worked again, didn’t have any time to check the build, and don’t really know what to look at. When I get home from work, what should I check first? ---
**Author:** ![TylerTheFolf](https://avatars.discourse-cdn.com/v4/letter/t/c5a1d2/32.png) [@TylerTheFolf](https://lookmumnocomputer.discourse.group/u/TylerTheFolf)\ **Post date:** [June 17, 2022, 10:57am UTC](https://lookmumnocomputer.discourse.group/t/ms20-vcf-not-working/5167/2 "2022-06-17T10:57:01Z")
Check for any shorts? Ive accidentally shorted the -12 to gnd before and the short protection of my powersupply kicked in. Could also be a over current thing? not sure… ---
**Author:** ![analogoutput](https://yyz2.discourse-cdn.com/free1/user_avatar/lookmumnocomputer.discourse.group/analogoutput/32/29663_2.png) [@analogoutput](https://lookmumnocomputer.discourse.group/u/analogoutput)\ **Post date:** [June 17, 2022, 11:12am UTC](https://lookmumnocomputer.discourse.group/t/ms20-vcf-not-working/5167/3 "2022-06-17T11:12:28Z")
> [@General advice for troubleshooting a module and asking for help](https://lookmumnocomputer.discourse.group/t/general-advice-for-troubleshooting-a-module-and-asking-for-help/2049): > > (This is a wiki post, please add and correct!) Look and see if others have had the same problem. Use the Discourse search facility to find topics where the module you’re building is discussed. Inspect your work. Verify all components are correct values. Look for solder connections that are rough, irregular, skimpy, dull, or missed completely (we all do that!) and reflow them. Look for solder bridges between pads and remove them. Check your power connection. If it’s a Eurorack style power cabl… ---
**Author:** ![Dave](https://avatars.discourse-cdn.com/v4/letter/d/ee7513/32.png) [@Dave](https://lookmumnocomputer.discourse.group/u/Dave)\ **Post date:** [June 17, 2022, 5:16pm UTC](https://lookmumnocomputer.discourse.group/t/ms20-vcf-not-working/5167/4 "2022-06-17T17:16:25Z")
I wonder if that post should be pinned to the top of the forum, It does seem to get linked to a lot as it is not immediately obvious to forum newcomers, and I feel most forum members have referred to this. ---
**Author:** ![Sonosus](https://yyz2.discourse-cdn.com/free1/user_avatar/lookmumnocomputer.discourse.group/sonosus/32/13679_2.png) [@Sonosus](https://lookmumnocomputer.discourse.group/u/Sonosus)\ **Post date:** [June 17, 2022, 8:51pm UTC](https://lookmumnocomputer.discourse.group/t/ms20-vcf-not-working/5167/5 "2022-06-17T20:51:08Z")
It’s pinned in the FAQ category, no? I wonder if we should go a step further and make it into a banner at the top of the forum that all users see (it can be dismissed). ---
**Author:** ![ChristianBloch](https://yyz2.discourse-cdn.com/free1/user_avatar/lookmumnocomputer.discourse.group/christianbloch/32/56_2.png) [@ChristianBloch](https://lookmumnocomputer.discourse.group/u/ChristianBloch)\ **Post date:** [June 18, 2022, 3:19am UTC](https://lookmumnocomputer.discourse.group/t/ms20-vcf-not-working/5167/6 "2022-06-18T03:19:22Z")
Reversed power header perhaps? ---
**Author:** ![hansun](https://avatars.discourse-cdn.com/v4/letter/h/bc8723/32.png) [@hansun](https://lookmumnocomputer.discourse.group/u/hansun)\ **Post date:** [June 22, 2022, 3:37pm UTC](https://lookmumnocomputer.discourse.group/t/ms20-vcf-not-working/5167/7 "2022-06-22T15:37:06Z")
So, I found some shorts and removed them. When I plugged it in after removing the shorts the psu is acting normal, I got a little hiss but no sound, I checked it again and the next time I plugged it in, nothing at all. The opamp gets really hot, like I cant even touch it, it smells a little funky too. Could the opamp have broken with the shorts and that’s why it gets so hot or is something else wrong? I’ve looked at the build and cant find any component in the wrong place etc. Almost feels like there still should be a short for it to get so hot? I don’t even dare have it plugged in so I can check it with a meter. ---
**Author:** ![analogoutput](https://yyz2.discourse-cdn.com/free1/user_avatar/lookmumnocomputer.discourse.group/analogoutput/32/29663_2.png) [@analogoutput](https://lookmumnocomputer.discourse.group/u/analogoutput)\ **Post date:** [June 22, 2022, 5:49pm UTC](https://lookmumnocomputer.discourse.group/t/ms20-vcf-not-working/5167/8 "2022-06-22T17:49:57Z")
You probably have one or more of the following problems: - IC is installed backwards. You can tell just by looking. If you don’t know how to tell which end of an IC is which, see [here](https://www.instructables.com/Integrated-Circuits-1/). Also make sure the chip is seated properly and all pins are actually in the socket, not bent under. You did use a socket, right? With power turned off, you can check continuity between each IC pin and the socket pad. - There are wrong voltages on the power pins. With power turned off, check continuity between the power rails and the ICs: Make sure any +12V pins connect to +12V power, -12V pins to -12V, ground pins to ground, +5V pins if any to 5V regulator. Check the datasheet or ask here if you don’t know which IC pin is supposed to connect to each. If there are series resistors or diodes on the power rails, you will need to check continuity from the other sides of those. As an additional check you can remove the IC, apply power, and measure voltages at the power pin locations, but probably wait to do that until you check: - Non power pins are shorted to power rails. With power turned off, check continuity between other pins and +12 V, -12 V, and ground. In some cases continuity is okay and in fact part of the circuit design, but in particular op amp output pins (pin 1 on a TL071, pins 1 and 7 on a TL072, pins 1, 7, 8, 14 on a TL074) should not be shorted to ±12 V or ground. For other pins consult the schematic or stripboard layout to see if the connection is intentional. If there is no continuity there still might be a problem if there’s a low resistance to a power rail, so go back over it with the resistance measurement setting and be suspicious of anything below about 1k or so. And, again, if there are diodes or resistors on the power rails, check back to them, not all the way back to the power inlet. - Chip is damaged, defective, or mislabeled. Always possible, and you can try swapping in a new chip to see if it works, but the chip might be running hot because it’s damaged or it might be vice versa — in the latter case, swapping in a new chip will just result in frying another chip, so don’t try it until you’ve exhausted other possibililties.