Class D Subwoofer Amplifier Repair - Page 1
Forum section: electronics / repair

author: geoffagain
author_rank: Contributor
timestamp: June 01, 2024, 09:21:40 am
content: *edit updated attached schematicHi gang,Have a BKA-130-C Buttkicker amplifier that is stuck in standby mode.Can anyone help with methodical fault finding please?Attached pic of board and schematic.I have component tested the momentary buttons and the the two IRF740 mosfets which are ok.The board looks to have got hot around the 'remote' connection - I've reflowed the four resistors R426 R427 R428 R169 and transistors Q404 and Q405 which also tested ok with a DMM.Powers on, but standby light remains red. Pressing power momentary switch I can hear relay click but led remains red and no output.Am I right in thinking the fault protection is controlled by the irs2153D? I'm not sure how to test.

author: Harry_22
author_rank: Frequent Contributor
timestamp: June 01, 2024, 07:43:37 pm
content: Hi!1. Check voltage at SW105 pin1 =+12V2. Check voltage at (-) D403 =+12V3. Check voltage at (+) D403. It grow slowly up to +6V and falls every time you press On (SW105) button.4. IC403 pin 1. It changes from 0V to +12V or back every time you press On button.PSSeems it works if you hear relay. Sorry I missed this.

author: Harry_22
author_rank: Frequent Contributor
timestamp: June 01, 2024, 08:04:20 pm
content: Carefully measure voltage between pin 1 and 4 of IC201A.Next measure between pin 3 and pin 4.Make sure the amplifier is turned on.

author: geoffagain
author_rank: Contributor
timestamp: June 01, 2024, 09:33:10 pm
content: Thanks for the guidance.As it happens IC201A on the schematic is listed as a L6569ADOn my board as I mentioned but didn't click its a irs2153D - still a gate driver.I've attached here another schematic I've found that lists the irs2153D - I'll try and update the original post too.I'll test it as described in anycase.Thanks

author: Harry_22
author_rank: Frequent Contributor
timestamp: June 02, 2024, 09:38:41 am
content: Two almost identical diagrams but drawn differently.The second one is completely unreadable. I mean it's hard to understand.PSI attached the first one as an example.

author: geoffagain
author_rank: Contributor
timestamp: June 02, 2024, 10:26:15 pm
content: IC201APin 1 and 4Main power on - 0vPressing momentary power switch on front - 6.5VPressing momentary power switch again - drops slowly to 0vPin 3 and 4Main power on - 0vPressing momentary power switch on front - 3.4mVPressing momentary power switch again - drops slowly to 0vRelay is operating, front led indicator remains in 'standby'Thanks for attaching the schematic again, I found second easier to follow but I shouldn't have assumed same or others

author: Harry_22
author_rank: Frequent Contributor
timestamp: June 03, 2024, 01:56:08 pm
content: Please measure voltage on R201 both sides.Be careful!

author: geoffagain
author_rank: Contributor
timestamp: June 03, 2024, 04:17:59 pm
content: we have on R201with momentary power button pressed and relay activating >-148V to ground155V to groundpressing power button again relay disengaging voltage drops slowly

author: Harry_22
author_rank: Frequent Contributor
timestamp: June 03, 2024, 05:21:07 pm
content: Let me clarify.1. R201 one side to pin 4 IC2012. R201 second side to pin 4 IC201One should be 320VDC next +16VDC.Please check.And measure R224 both sides between pin 4 IC201.

author: geoffagain
author_rank: Contributor
timestamp: June 03, 2024, 06:47:31 pm
content: ok that makes more senseWe haveR201325V and7.48VR2246.88V and 6.86V

author: Harry_22
author_rank: Frequent Contributor
timestamp: June 03, 2024, 07:53:48 pm
content: Great!The diagnosis can already be made. Lack of voltage to start the IRS2153 controller.The rectified high tension 325V passes through resistor R201 and forms a voltage drop 16V across ZD201 zener diode which powers the controller. In our case, only 7.5V is generated at the zener. The conclusion is that something is lowering the voltage.To clarify this please firstdisconnect equipment from the mains.Measure resistance between D210 anode and pin 4 of IC201.Next measure resistance between D210 cathode and pin 4 of IC201.

author: geoffagain
author_rank: Contributor
timestamp: June 03, 2024, 08:26:58 pm
content: Great annotation to the diagram, thank you for explaining. It's helpful to understand the circuit.We have on the board measured at the zener ZD210D210 anode and pin 4 of IC201 - 0hmD210 cathode and pin 4 of IC201 - rises quickly to OL then drops and settles at 9.6Kohm

author: Harry_22
author_rank: Frequent Contributor
timestamp: June 03, 2024, 09:19:40 pm
content: The zener diode is most likely broken.

author: David_AVD
author_rank: Super Contributor
timestamp: June 03, 2024, 10:02:14 pm
content: I had a leaky Zener in a SMPS the other week. The leakage was enough to pull the rail below the Vmin.

author: geoffagain
author_rank: Contributor
timestamp: June 04, 2024, 05:26:29 pm
content: Thanks for this,I replaced the zener with another from a donor board - still could be broken, I need to test both of them still.Same voltage at R201I pulled R201 and it reads correct resistance out of circuit.

author: geoffagain
author_rank: Contributor
timestamp: June 04, 2024, 07:39:59 pm
content: Ok so Zener in circuit ZD201 is 1N4744 15vThe one I pulled from donor is also marked IN4744. So seems for whatever they're using 15V rather than 16V on this one.Tested ZD201 out of circuit with my bench supply and a 1k resistor -Seems ok, holds 15v upto the 20v I can supply. Not sure on leakage current.I'm not measuring any current or at least very minimal under 15V with a 1k resistor in series.Approx >0.5mA at 15V1mA at 16V2mA at 17V3mA at 18V

author: Harry_22
author_rank: Frequent Contributor
timestamp: June 04, 2024, 07:43:55 pm
content: Measure the resistance between D210 anode and pin 4 of IC201.There are also C209 capacitor in parallel with the zener.

author: geoffagain
author_rank: Contributor
timestamp: June 04, 2024, 08:17:04 pm
content: Cheers for your continued patience.Resistance between D210 anode and pin 4 of IC201 - same behaviour as before withD210 cathode and pin 4 of IC201 - rises quickly to OL then drops low then rises and settles at 9.6Kohm - perhaps still rising very slightly over time.I'll pull c209 and see what my ESR says.

author: Harry_22
author_rank: Frequent Contributor
timestamp: June 04, 2024, 08:30:28 pm
content: But with Zener you had 0 Ohm. Am I right?

author: geoffagain
author_rank: Contributor
timestamp: June 04, 2024, 08:49:57 pm
content: SureZD201 anode to pin 4 is 0hm

author: geoffagain
author_rank: Contributor
timestamp: June 04, 2024, 09:16:13 pm
content: C209 was crapped out open circuitreplaced with a good cap but no joy.I may visit some of the other caps as this one didn't show any visual signs of failure

author: Harry_22
author_rank: Frequent Contributor
timestamp: June 04, 2024, 09:24:33 pm
content: Anode ZD201 is connected to pin 4 of IC.Yestrday you measured anode D210 to pin 4 and resistance was 0.Ok let us solder ZD201 back and pull D210.After connect the device to mains and check voltage on Zener.

author: geoffagain
author_rank: Contributor
timestamp: June 04, 2024, 09:50:01 pm
content: ApologiesIt's likely I made a mistake between ZD201 and D210For clarity we haveD210 cathode to pin 4 - 69.5KohmD210 anode to pin 4 - 9.6KohmZD201 cathode to pin 4 - 9.6KohmZD201 cathode to pin 4 - 0ohmPulling D210 and checking zener voltage on ZD201Rises to 14.93v

author: Harry_22
author_rank: Frequent Contributor
timestamp: June 05, 2024, 10:04:45 am
content: No need to apologize it's also my mistake.If the resistance was zero then there would be no voltage on Zener. I could notice right away.I forgot to warn you that in non-working SMPS the high tension remains on capacitors for a very long time.In your case two caps are connected in series and loaded with resistors to equalize potentials. Just like in valve amps. It turns out that 195uF is discharged through 360k. Time constant R*C=70s. In a time of 3*70s the caps will be discharged by 95% to a safe value.Please wait at least 3 minutes before touching SMPS !Now we will work with SMPS disconnected from mains.Let's use your 1k resistor and bench supply.Please connect it via a 1k resistor to 1 pin Vcc of the IC. Ground to pin 4 (pls see the picture). Voltmeter between pins 1 and 4 of the IC.Gradually increase the voltage and monitor following stages:1. Voltage on Vcc will rise until startup point ( between 10-12V according to datasheet). The current through IC is very small and Vcc is equal to the voltage on the bench supply.2. Startup point. You will see 1.7V difference between PS and Vcc. The controller begins to draw 1,8mA current which creates a drop across the resistor.3. At 15,4V Vcc growth will stop as with Zener. Because IC has its own Zener inside.

author: geoffagain
author_rank: Contributor
timestamp: June 06, 2024, 08:00:38 pm
content: Good advice on caps - if not for me then for anyone else coming across this thread.Can't get a stable voltage when connected to my bench supply, its not happy in the slightest.I've got current limiter set at 100mA so unless its sinking more than that I have no idea what is happening. Should be plenty of headroom for 20mA (20v @ 1kohm) plus 1.8mA from the controller.Bench supply is probably crappy, its hardly a reference device - not clamping voltage down quickly enough or hitting current limiter or both ..etcResistance between pin 1 and 4 is 1.12 KOhm

author: Harry_22
author_rank: Frequent Contributor
timestamp: June 06, 2024, 10:21:55 pm
content: Measuring the resistance of active elements is purely for estimation purposes.From calculation of your previous measurements it follows that the equivalent leakage resistance is 3,3k.Most likely the controller is faulty.But first unsolder R224 switch on SMPS and measure the voltage on Zener diode.

author: geoffagain
author_rank: Contributor
timestamp: June 06, 2024, 11:23:31 pm
content: Looks that wayWithout R224 we have 14.98V at zener - same as tested out of circuit.i have a donor board, is it worth swapping the IC out or is there a reason its blown?

author: Harry_22
author_rank: Frequent Contributor
timestamp: June 07, 2024, 05:17:06 pm
content: Quote from: geoffagain on June 06, 2024, 11:23:31 pmPlease remember what events preceded the failure of SMPS?

author: geoffagain
author_rank: Contributor
timestamp: June 07, 2024, 08:21:10 pm
content: I'm not sure.Have more than one of these amps that are presenting in standby. The one I'm using as a donor board has a short across the TDA chip. It seems these amps have a lot of problems but not a common point of failure.Thanks