Comments on: Main SMPS Transformer Overheated https://jestineyong.com/main-smps-transformer-overheated/ Semiconductors, Test Equipments, Circuit Board Troubleshooting, Electronic Repair Courses and Many More! Sat, 17 Dec 2022 04:07:18 +0000 hourly 1 https://wordpress.org/?v=5.4.19 By: Sean McKinnon https://jestineyong.com/main-smps-transformer-overheated/comment-page-1/#comment-398678 Sat, 17 Dec 2022 04:07:18 +0000 https://jestineyong.com/?p=19597#comment-398678 Hi Riaan,
I am currently trying to fix my friends keyboard with the same failed power supply - but I'm stuck. I did learn from the TDA4605 manual that there is a no-load "safety function" that limits the pulse duration on pin 5 to "render the circuit absolutely safe under no-load conditions"... which could explain why you needed the 100 ohm resistor without the keyboard. Anyways, I've checked almost everything on the board, and I'm thinking I need to replace the TDA4605 chip and was wondering where you were able to source one? FYI, I see the output voltages rising and falling kinda like you described, but even with the PS plugged into the keyboard.
One thing I was hoping you could explain is the function of pin 2, the manual states the following: "A voltage proportional to the drain current of the switching transistor is generated there by the external RC-combination in conjunction with the primary current transducer. The output of this transducer is controlled by the logic and referenced to the internal stable voltage V2B. If the voltage V2 exceeds the output voltage of the regulations amplifier, the logic is reset by the stop comparator and consequently the output of pin 5 is switched to low potential. Further inputs for the logic stage are the output for the start impulse generator with the stable reference potential VST and the supply voltage motor"
Shouldn't the voltage be inversely proportional to the drain current??
Thanks for your time and effort!!
Sean

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]]> By: Rhey https://jestineyong.com/main-smps-transformer-overheated/comment-page-1/#comment-358432 Tue, 04 Jun 2019 07:30:31 +0000 https://jestineyong.com/?p=19597#comment-358432 Excellent

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]]> By: Yogesh Panchal https://jestineyong.com/main-smps-transformer-overheated/comment-page-1/#comment-357992 Fri, 24 May 2019 14:29:08 +0000 https://jestineyong.com/?p=19597#comment-357992 Schematic is very helpful to understand working process path.
Good Job!
Thanks for sharing.

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]]> By: Ghashaan https://jestineyong.com/main-smps-transformer-overheated/comment-page-1/#comment-357869 Wed, 22 May 2019 11:39:13 +0000 https://jestineyong.com/?p=19597#comment-357869 In reply to abdellah kamli.

That's a sweet explanation.

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]]> By: abdellah kamli https://jestineyong.com/main-smps-transformer-overheated/comment-page-1/#comment-357827 Tue, 21 May 2019 21:33:09 +0000 https://jestineyong.com/?p=19597#comment-357827 In reply to Ghashaan.

Hi Ghashaan,your clever comment lets pointing a sensitive question.In attempt to bring a response I would like to share this modest explanation: when the output is fluctuating this means it oscillates at some frequency, by loading the output with the resistor it cancels the oscillations. The output capacitors, it seems, act with the resistor 100 Ohm as a low pass filter RC in which the equivalent capacitor has a high impedance at low frequencies so that the major energy is directed to the mass and the current flows through the resistor allowing a stable output voltage.
CHEERS

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]]> By: Parasuraman Subramanian https://jestineyong.com/main-smps-transformer-overheated/comment-page-1/#comment-357814 Tue, 21 May 2019 15:04:09 +0000 https://jestineyong.com/?p=19597#comment-357814 Very Good article packed with very useful hints and ways. Getting a replacement for an SMPS Tx is not even heard of in our area. So, I am amazed to see the kind of support you all get there!

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]]> By: Albert van Bemmelen https://jestineyong.com/main-smps-transformer-overheated/comment-page-1/#comment-357813 Tue, 21 May 2019 14:38:38 +0000 https://jestineyong.com/?p=19597#comment-357813 Interesting repair with useful schematic.
Since the transformer was internally shorted, replacing the controller IC at first obviously made no difference.
Since the BUZ90 mosfet already had gone, most likely the original TDA4605-2 controller IC had gone too. Why it would be best to replace that controller IC to a new TDA4605-3 controller IC after you had replaced the bad transformer. This way taking no chances in blowing up the mosfet and the transformer again.

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]]> By: Ghashaan https://jestineyong.com/main-smps-transformer-overheated/comment-page-1/#comment-357808 Tue, 21 May 2019 14:04:33 +0000 https://jestineyong.com/?p=19597#comment-357808 Good job!

I learned something important from your article. If the output voltage is fluctuating, I should try with a load in order to stabilize the output. But I still wonder why this trick is required for some power supplies and not for all!

I enjoyed reading your article!

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]]> By: John Shadbolt https://jestineyong.com/main-smps-transformer-overheated/comment-page-1/#comment-357807 Tue, 21 May 2019 13:54:18 +0000 https://jestineyong.com/?p=19597#comment-357807 Great repair, lucky that Roland had the matching transformer. Did you check the output capacitors? It might be the camera, but the one right next to a heatsink looks bulged, a replacement would probably be smaller so less likely to get dried out.

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]]> By: Justice https://jestineyong.com/main-smps-transformer-overheated/comment-page-1/#comment-357805 Tue, 21 May 2019 13:36:40 +0000 https://jestineyong.com/?p=19597#comment-357805 Great article Riaan. I am excited to hear someone from my home country, great job .

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