Kunkin KP182 Loud Screaming - Page 1
Forum section: electronics / testgear

author: boful
author_rank: Contributor
timestamp: March 19, 2022, 01:03:34 am
content: Greetings.Kunkin KP182 appears to work, tested with loads between 5W and 100W ..However, a very loud high pitch sound has appeared.Attached audo file is with no load, just power on. Havinga load does not change sound. Sound appears to becoming from motherboard somewhere.Motherboard is Rev 03.Could see nothing visual wrong. Looked at forum threadsdid not see anything similar. Also did not see schematics.Please any comments.Thanks so much ..

author: bob91343
author_rank: Super Contributor
timestamp: March 19, 2022, 06:46:07 am
content: Get a tube and localize the source.

author: Fungus
author_rank: Super Contributor
timestamp: March 19, 2022, 11:25:55 am
content: It's usually an inductor.Get a plastic tube, put one end in your ear and use the other end to listen to components on the board.

author: boful
author_rank: Contributor
timestamp: March 20, 2022, 03:02:33 pm
content: Update ..It's the fan that is making the loud sound.Please, the fan is specificed 12Vdc (7-13.8v) part number AFB0812SH4 Pin Fan.The 12 Vdc fan supply, from the motherboard to fan measures 16Vdc .. and has 1Vpp rippleat 120Hz. Traced out the schematic, the 12Vdc is generated from a transformer tap, to rectifer bridge andfilter cap. No dropping resistor etc, straight connection to the fan 4 pin connector. The wiring to the fanwas point to point. Verifed the brige rectifer, filter cap etc.The output from the transformer is 13 Vac rms ... This seems to high ?13Vac rms will be around 16Vdc from the rectifer bridge.The transformer has NO markings, nothing.Could the transformer voltage be to high ? Am I just spinning in circles.I would give a cookie for a schematic :-)thanks

author: bob91343
author_rank: Super Contributor
timestamp: March 20, 2022, 05:34:01 pm
content: Maybe just a bad bearing in the fan motor.

author: armandine2
author_rank: Frequent Contributor
timestamp: March 20, 2022, 05:48:56 pm
content: isn't this where you test your hypothesis ?- inject a good 12VDC and listen

author: boful
author_rank: Contributor
timestamp: March 20, 2022, 07:10:02 pm
content: Greetings.I tried your suggestion. Used a spare 4 pin connector and connected a quailty power supply 11-16Vdc to the fan. With No PWM or Sense signal connected from the motherboard, fan ran full speed, NO squealing sound.Then connected motherboard Sense signal, same results.Then connected motherboard PWM signal, and * YES * , horrid squealing, at the lower RPM.Looked at PWM signal on scope and it looks like a good signal.GUESSING either the fan does not like PWM operation or its the 16Vdc applied to the Fan is causing a problem.Wish I knew if the Transformer ouptput voltage suppling the fan was the correct design value. Just seems high.Thanks so much for the suggestion.

author: boful
author_rank: Contributor
timestamp: March 27, 2022, 03:40:29 am
content: Greetings.Follow Up with fan screaming high frequency sounds on the KP182.Installed a new fan and problem is gone.However, the voltage supply to the fan is still 15Vdc as describedin previous post. The rating on the fan is max 13Vdc.To me it appears either the Vac transformer is bad or it's a designproblem.If anyone has a KP 182 or KP-184 and gets bored, it's easy tomeasure the fan supply voltage, a 4-pin connector on top of the motherboard.Would love to know if it's a design problem.Thanks so much.

author: Fungus
author_rank: Super Contributor
timestamp: March 27, 2022, 07:31:50 am
content: Helluva design problem if so... the voltage on the fan is clearly labelled and it only takes one resistor to fix it.