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Repair of Axpert Inverters : A Journey Started


BritishRacingGreen

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On 2024/06/19 at 4:21 AM, BritishRacingGreen said:

Further to this I  tested the semiconductors of the RED interleave driver circuits. All semiconductors blown short or open circuit , except the 3 mosfets.  

The IR2011 driver blown and all six of the buffer amplifier transistors blown short circuit!

Wow. That's some carnage. But I guess it's a great way to learn repair of these things. It almost has one of every possible fault to learn from! 

On 2024/06/19 at 4:21 AM, BritishRacingGreen said:

I cannot thank you enough for all the resources you provided us.

Aw, shucks! Thanks for the kind words, and I'm glad my work has been useful to you. 

18 hours ago, BritishRacingGreen said:

The power stage is relatively small for a 3/4/5kW capable SCC in relation to that of say the LV DC side of the main board.

Yeah, interesting. Part of that is you need a full bridge in the DC-DC converter low side, for bidirectional power flow. So that's 3/4 of the MOSFETs you don't need. The full bridge has double the I²R losses, since both legs are switched in the DC-DC, so it only needs half the heatsink. 

19 hours ago, BritishRacingGreen said:

Is the PWM frequency of SCC less than that on main board?

If so, while I am aware that switching losses is dependant on frequency, is this also true for conduction losses? (source-drain). 

I would think that the switching frequency is similar. Conduction losses are independent of frequency. 

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19 hours ago, BritishRacingGreen said:

2. I see the use of 5 pin 2 input AND gates on the SCC pwm drives. Is this some kind of failsafe gate to negate drive pulses during times when the CPU outputs are indeterministic, eg at bootup etc.?  If memory serves they are also employed on the DSP board of the host machine. 

On the control board, I thought that they were D flip-flops, but maybe AND gates makes more sense. As for what they are there for, I really don't know. You may be right about killing the outputs when the DSP is reset or similar.

Pardon the piecemeal replies. I'm without power today, having the house switchboard upgraded. So this is from my phone, and your post is on the previous page. 

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19 hours ago, BritishRacingGreen said:

4. I notice debates regarding LV SCCs versus HV SCCs. I know @Coulomb prefers the former because, amongst other, of its exposure to AC live.

Interesting points. I guess I'll be forced to use high PV voltage systems eventually, as Voltronic might phase out the low PV voltage ones, except perhaps for some smaller 24V models, which aren't suitable for me. I certainly see the value in being able to blend AC-in and solar. 

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19 hours ago, BritishRacingGreen said:

3. I take it the totempole style buffer amps after the IR2011S gate driver is required because of  the  fanout of 3 mosfets as opposed to a single one. 

Yes, I'd say that's the reason. MOSFETs have significant gate capacitance that has to be charged or discharged quickly, meaning amps of current for short periods of time. Initially I thought that the IRS may be there to guarantee dead time, but that makes no sense here, I think. Unless you can't have both sides of the interleaved design on at once.

Edit: I guess if they allowed both sides on at once, there would be spikes of double current, which would not be good.

The AND gates might be for enforcing dead time as well, but it makes no sense to have both. Especially in an economy design. 

Edited by Coulomb
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On 2024/06/18 at 7:29 PM, BritishRacingGreen said:

The dreaded ERROR 09 , it always spells nasty failure of the components in the power chain. 09 is Bus Soft Start fail , it means the controller has detected a short circuit on the High Voltage DC bus. SO expect a number of IGBTS blown , together possibly with driver circuits as well.

 

Yes , even if you are using a current limited bench supply , you must remember it initially charges the low and high DC bus capacitor banks to their full capacity. This storage has enough energy then adequate to destroy the IGBT's and MOSFETS spectacularly  .

I feel your pain , I have had similar experiences in the pass , so I have a couple of walkthroughs in this thread  to bring up the dc-dc converter in a very graceful and soft manner. Also the DC-AC converter can be verified in this manner .

 

Finally all's well that ends well. Replacing the IGBTs and molly-coddling it during start-up revived the inverter. Altho the failure mechanism for the IGBTs is still a grey area, the customer is happy so what else can I say. Thanks to @BritishRacingGreen @Coulomb @wael_fathe and others for the insight and information this forum has provided. I'm not yet expert level but I'd like to think I'm on the way there if more inverters come my way.

 

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16 minutes ago, Mach4 said:

Finally all's well that ends well. Replacing the IGBTs and molly-coddling it during start-up revived the inverter. Altho the failure mechanism for the IGBTs is still a grey area, the customer is happy so what else can I say. Thanks to @BritishRacingGreen @Coulomb @wael_fathe and others for the insight and information this forum has provided. I'm not yet expert level but I'd like to think I'm on the way there if more inverters come my way.

 

you're welcome . Although I inferred that you have an engineering background and that must have  pulled the wagon thru the river drift.

Well done !

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Posted (edited)
On 2024/06/20 at 3:11 AM, Coulomb said:

Yeah, interesting. Part of that is you need a full bridge in the DC-DC converter low side, for bidirectional power flow. So that's 3/4 of the MOSFETs you don't need. The full bridge has double the I²R losses, since both legs are switched in the DC-DC, so it only needs half the heatsink. 

Ah yes , of course you are right on the money . A full bridge requires more silicon and therefore more heat sink , as two elements are switching per cycle. Whereas a half bridge over a center split transformer  primary  only has one switch that is on per cycle. 

 

On 2024/06/20 at 3:18 AM, Coulomb said:

On the control board, I thought that they were D flip-flops

This prompted further investigation as I might have misinterpreted things. Indeed the SMD marking on the device on the SCC is VT7 . Now there is actually a VT marking for a 5 pin positive edge trigger D-type flip flop. And its pinout is consistent with pin 3 GND , pin 4 Q output  , pin 5 VCC  and pins 1 & 2 being inputs. So it could be very well be the d type flip flop . 

 

https://www.ti.com/product/SN74LVC1G80?bm-verify=AAQAAAAJ_____9eqwI2wT8gpqW3O3PmcoLpsGRDdH_CHBRiYf8_42Cy-D0VokuJDegbNBiVszuWNr3DUTmMHQaJFCTkYxRDw3Sy6yGYHoaaUq_YvcBGZXvO6SMjX8ZV6kQesF4Nd9uDl3V5GBosOM3ujq5sm7ojNvrqMmlyDvdD8rIdziHH2V6qxipy1FMuhHJs_48utA5WJcfGdaKp9uYWUEZiLwz-R-_kWv_h5quT0h3rdQCtQcO4ZLbjyhZMfL-KBSWfuJMRVk9Ehtb-oNyTNXmunYsdXToEd_4rOSblIoC56Jt_0vUivO8in_7NUbw

 

Edited by BritishRacingGreen
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13 hours ago, BritishRacingGreen said:

Whereas a half bridge over a center split transformer  primary  only has one switch that is on per cycle.

True. But we're comparing with the MPPT's boost converter, which is essentially one switch that is on per active part of the cycle. Though I suppose you have to add one diode drop that the DC-DC converter doesn't have. Though that 0.5 V drop over say 250 V is only 0.2%.

Perhaps the main reason is that the DC-DC converter is operating at around 5x lower voltage, and so 5x higher current, so the I²R losses are 25x for the DC-DC (if the silicon (the R) was the same, but it's not).

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On 2024/06/16 at 4:20 PM, Coulomb said:

That surprised the heck out of me too when I first heard about it. I think it has something to do with batteryless operation.

I think that they just have to use a higher voltage MOSFET or IGBT, and of course the bypassing capacitor. The "transformer" turns ration possibly needs to be tweaked as well, but that's not a huge issue.

These flyback converters can apparently accommodate a fairly wide range of input voltages.

I'm not convinced that this EASun is a clone. And I'm 98% sure that the 150 V bus is a Voltronic design, not a clone design. EASun seem to have a slightly different relationship with Voltronic than the usual resellers; they appear to be manufacturers in their own right. Quite possibly "reformed" clone manufacturers (or threatened with legal action, whatever). Inverex seems to be another manufacturing reseller, that licences the basic design and firmware from Voltronic, but makes the product themselves (I'm guessing).

But requiring another DC-DC converter does seem crazy. 60 V seems to be a much better choice, but I guess it makes the battery a power source of last resort. Often you want that, perhaps there are times when you don't.

Mr colomb...easun has not seperate sps for 150vdc....am refering to sun on pro solar inverter from sakko manufacturer ...still in negotiations with company the promise to provide help and schematics for thier 3 k new yet  dead inverter  once they provide it we will discuss it here 

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On 2024/06/16 at 7:49 PM, BritishRacingGreen said:

Yes that is normal , because the initial bootstrap is only there for short while. In that period the SMPS should produce , and amongst other , will generate the +15VDC supply over C75 , which will power U10 via D49  even after the bootstrap via D50 falls away. But because your SMPS does not deliver , when the bootstrap via D49 falls away , everything collapses.

 

The following test is provided to statically test the SMPS negative feedback loop. While no attempt is made to verify the linearity of the transfer function , it is adequate to test the extreme low point of feedback (resulting in highest output duty cycle) , as well as the high point of feedback (resulting in lowest possible output duty cycle) . To do so , we will manually power up the U10 and support circuitry with a power supply of 15V , and manually inject a variable 12V supply on the +12V output rail in order to fool the U10 that it is 'regulating'.

1. Remove all ancillary connections external from the main board , including controller board , fans , mppt , battery , everything.

2. You will require 2 x 12V variable bench supplies and an oscilloscope . Both of them must be current limited and both must be able to vary up to +15VDC.

3. Connect psu 1  positive to D57 cathode and negative to BAT- and set to +15VDC  . Current limit to 100mA or so. This will provide a steady VCC  on U10 pin 7 and power the chip .

4. Check there is steady +5V on U10 pin 8.

5. Check with oscilloscope that there is frequency and 50% (max) duty cycle on the gate of mosfet Q36 .  

6. Connect psu 2 set to 11.7 V between D54 cathode and GND . Set current limit to 800mA. This will false feed the +12V bus. At 11.7V the U10 output duty cycle should still max out at 50%. Check that the voltage drop over U8 diode is well below 1.1V . PLEASE NOTE : by injecting this 12V supply remember that the 12V loads on the main board is still connected . So please make sure that you dont push this voltage higher than say 12.8V.

7. Increase the psu to 12V and measure the TL431 bias voltage over R209 . It should be very close to 2.5V . Increase the psu to 12.5V and make sure the bias voltage is above 2.5V. at this stage TL431 turns hard on and current flows thru the U8 diode. The voltage across this diode should saturate at approximately 1.1V. This will in turn turn the U8 transistor hard on on the SMPS primary side . In turn this will pull the COMP pin 1 of U10 well down to 0V . As a result of this , U10 must correspond by outputting  its lowest duty cycle on its output  to the mosfet gate.

8. If all of this passes , the feedback loop circuit is pretty much in order.

... I will continue with this in another post  whereby you can bring the SMPS up with starting with a small 10V voltage at its dc input and working our way up to 40V if all goes well ...

 

Excited  to do it ...fake12vdc at out cap will fool ic ...we.will expext changing pwm if change vdc at output cap..hmmm  .interesting

 

Today an engineer from sakko   sent me screenshot of feedback circuit of sunon pro 3k 24vdc solar inverter  as i knocked down resistor r105 ..so he sent shot ....how close that to voltronics...hoping for the entire smps and battery sps to be sent

IMG-20240620-WA0005.jpg

Edited by wael_fathe
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On 2024/06/20 at 7:45 PM, BritishRacingGreen said:

you're welcome . Although I inferred that you have an engineering background and that must have  pulled the wagon thru the river drift.

Well done !

Congratulations bro...togetherness is key for technicians to survive in modern day hostile environment ..hostile because manufacturer are not willing to gave any schematics and real manuals and guides... congrats bro again

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4 hours ago, wael_fathe said:

.so he sent shot ....how close is that to Voltronics...

It's pretty close; here is Maxo's traced schematic for that part of the circuit:

image.png.4f74c8a658bf21125958460be6fd5671.png

The resistor designators (e.g. R19) are different, but the IC designators are the same. R257 is half the value of the Voltronic (unless it's changed over the years). That 510Ω resistor in the emitter of U8 is not present in the Voltronic (again, unless it's introduced in later models). Though @BritishRacingGreen's schematic doesn't show these changes:

image.thumb.png.b0c786105ae060978a7d91fc9528c1bb.png

The capacitor across the RC network (39 nF versus 220 pF) probably was not checked by Maxo or by BritishRacingGreen out of circuit. 220 pF at a wild guess seems more reasonable, otherwise the 100k/49.9k resistor would have little effect.

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On 2024/06/20 at 7:26 PM, Mach4 said:

Finally all's well that ends well. Replacing the IGBTs and molly-coddling it during start-up revived the inverter. Altho the failure mechanism for the IGBTs is still a grey area, the customer is happy so what else can I say. Thanks to @BritishRacingGreen @Coulomb @wael_fathe and others for the insight and information this forum has provided. I'm not yet expert level but I'd like to think I'm on the way there if more inverters come my way.

 

Congratulations bro...

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11 hours ago, Coulomb said:

It's pretty close; here is Maxo's traced schematic for that part of the circuit:

image.png.4f74c8a658bf21125958460be6fd5671.png

The resistor designators (e.g. R19) are different, but the IC designators are the same. R257 is half the value of the Voltronic (unless it's changed over the years). That 510Ω resistor in the emitter of U8 is not present in the Voltronic (again, unless it's introduced in later models). Though @BritishRacingGreen's schematic doesn't show these changes:

image.thumb.png.b0c786105ae060978a7d91fc9528c1bb.png

The capacitor across the RC network (39 nF versus 220 pF) probably was not checked by Maxo or by BritishRacingGreen out of circuit. 220 pF at a wild guess seems more reasonable, otherwise the 100k/49.9k resistor would have little effect.

I have not checked all the issues raised yet  , but can start to confirm that U8 emitter is on hard BAT- and the collector is directly connected to U10 Pin1 (COMP) . So there does not exist a 510R resistor in this path  . This is on my 2 donor boards , one is 16-500893-01G(B) (pre MKS3) and the other one is 16-501421-02G(A) (MKS4).

 

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On 2024/06/21 at 6:45 PM, BritishRacingGreen said:
On 2024/06/20 at 3:18 AM, Coulomb said:

On the control board, I thought that they were D flip-flops

This prompted further investigation as I might have misinterpreted things. Indeed the SMD marking on the device on the SCC is VT7 . Now there is actually a VT marking for a 5 pin positive edge trigger D-type flip flop. And its pinout is consistent with pin 3 GND , pin 4 Q output  , pin 5 VCC  and pins 1 & 2 being inputs. So it could be very well be the d type flip flop . 

 

https://www.ti.com/product/SN74LVC1G80?bm-verify=AAQAAAAJ_____9eqwI2wT8gpqW3O3PmcoLpsGRDdH_CHBRiYf8_42Cy-D0VokuJDegbNBiVszuWNr3DUTmMHQaJFCTkYxRDw3Sy6yGYHoaaUq_YvcBGZXvO6SMjX8ZV6kQesF4Nd9uDl3V5GBosOM3ujq5sm7ojNvrqMmlyDvdD8rIdziHH2V6qxipy1FMuhHJs_48utA5WJcfGdaKp9uYWUEZiLwz-R-_kWv_h5quT0h3rdQCtQcO4ZLbjyhZMfL-KBSWfuJMRVk9Ehtb-oNyTNXmunYsdXToEd_4rOSblIoC56Jt_0vUivO8in_7NUbw

 

Sorry @Coulomb I have mistakenly re-identified the small 5 pin device as a d-type flip-flop . I can now confirm that it is indeed a 2-input AND gate as I originally discovered. The third digit on the SMD marking confused me . On this 5 pin device only the first 2 digits are significant in identifying the type , the third digit is a manufacturers date code marking. So I have on two different low voltage SCC's markings of VT7 and VTF , but they both actually VT and this decode to an on-semi MC74VHC1GT08 device. 

datasheet :https://www.lcsc.com/datasheet/lcsc_datasheet_1809111715_onsemi-M74VHC1GT08DFT2G_C99673.pdf

 

Interesting this guy in the link below was looking for marking VTM coming out of a Growatt inverter. So this confirms my understanding.

https://electronics.stackexchange.com/questions/702141/identify-5-pin-smd-component-marked-vtu

 

I need to buy a number of these devices tomorrow , but I can only get hold of C74VHC1G08 (without the T ).  The following datasheet shows both devices  https://www.mouser.co.za/datasheet/2/308/1/MC74VHC1G08_D-2315735.pdf .

I see the difference between them is the logic thresholds on the 2 inputs . The 'T' device has  TTL level specs , while the one that I can lay my hands on has CMOS (HC) specs. So if you have the model number perhaps of the host cpu on the LV SCC boards , I can check whether its digital outputs will be compatible with the inputs of the AND gate. I can tell that both the CPU and AND gate are powered by 5VDC.

 

 

 

 

 

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16 hours ago, wael_fathe said:

Excited  to do it ...fake12vdc at out cap will fool ic ...we.will expext changing pwm if change vdc at output cap..hmmm  .interesting

 

Today an engineer from sakko   sent me screenshot of feedback circuit of sunon pro 3k 24vdc solar inverter  as i knocked down resistor r105 ..so he sent shot ....how close that to voltronics...hoping for the entire smps and battery sps to be sent

IMG-20240620-WA0005.jpg

Brilliant , Thanks. You seem to have some good contacts with the right people.👌

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On 2024/06/18 at 3:05 PM, wael_fathe said:

there is one more strange thing about those  clone  inverters    even if both  smps are good

they work  for about 3 sconds  produce 120vdc ...-12  +12  5  then they shutdown

 

only when the control board inserted  , at that only case the work  fine   ,and continue witout a shutdown by the way 

Just a bit of feedback that the voltronics VM (II, III and IV) range has this same design.

With the control board removed I usually check for shorts on the power rails, then check the rails and the -5.4V on the output IGBTs gates by flicking the power on and off after injecting 30V at D74. I then test mosfets and DC-DC by powering +/-12V rails through the CN10 pins (not the same as Maxo's schematic), triggering the SG3524 by shorting U19 output and then checking all the gate signals. This can be safely done even with the mosfets and IGBTs installed as the battery and DC buses are unpowered.

It's been a while since I checked up on the forums so if there's been any testing improvements that I'm missing don't hesitate to point them out. I've recently had a bunch of machines with SPS failures so thanks @BritishRacingGreen for your recent test procedure it will be very handy!

*caveat: I use the component designators from Maxo's schematic, they are not all the same on the VM models so check the circuit before using any information posted above (one of these days I hope to start work on a schematic)*

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9 hours ago, Shadders said:

Just a bit of feedback that the voltronics VM (II, III and IV) range has this same design.

With the control board removed I usually check for shorts on the power rails, then check the rails and the -5.4V on the output IGBTs gates by flicking the power on and off after injecting 30V at D74. I then test mosfets and DC-DC by powering +/-12V rails through the CN10 pins (not the same as Maxo's schematic), triggering the SG3524 by shorting U19 output and then checking all the gate signals. This can be safely done even with the mosfets and IGBTs installed as the battery and DC buses are unpowered.

It's been a while since I checked up on the forums so if there's been any testing improvements that I'm missing don't hesitate to point them out. I've recently had a bunch of machines with SPS failures so thanks @BritishRacingGreen for your recent test procedure it will be very handy!

*caveat: I use the component designators from Maxo's schematic, they are not all the same on the VM models so check the circuit before using any information posted above (one of these days I hope to start work on a schematic)*

Hi @Shadders I trust you are well.thank you for valuable inputs. 

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12 hours ago, BritishRacingGreen said:

So if you have the model number perhaps of the host cpu on the LV SCC boards , I can check whether its digital outputs will be compatible with the inputs of the AND gate. I can tell that both the CPU and AND gate are powered by 5VDC.

I knew this part number at one point, but I could not find anywhere that I wrote it down. Sigh.

I happen to have a King 1 in for repair at the moment, so its SCC MPU sticker was sacrificed for science. It seems that these are NXP MC9S08AC48 chips, or at least that's their model number and marking (very hard to read).

I'd say you'll be fine with the non-TTL threshold AND gates, as long as there isn't a large load on the outputs:

image.png.2ef0a43b7c395bb3d6a83548e97cd0be.png

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Good news today..

The company gave me full schematic for both battery and mains sps  to help fix dead mains sps

I will ofcourse put them for benfit of good people ... battery sps  was really normal output of 150vdc...no doubt now ..

By the way this is the most clone design i have met..if well understood will open the gate for understanding alot of other makes and models

@Coulomb

@BritishRacingGreen

 

IMG-20240624-WA0001.jpg

IMG-20240624-WA0000.jpg

Edited by wael_fathe
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I think i am.close to find the problem of the low output in main sps...while changing the uc3845 i knocked timing capacitor...which changed the working frequency..which will effect the dc voltage  output , look at the feequncy..i forced the ic the produce waveform just fed 12vdc to pin7 ground to sensing resistor since it is always hooked to ground...got this wave form ...that is bad ..it cant be 1khz no way

@Coulomb

@BritishRacingGreen

 

20240624_183410.jpg

20240624_183432.jpg

Edited by wael_fathe
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1 hour ago, wael_fathe said:

I think i am.close to find the problem of the low output in main sps...while changing the uc3845 i knocked timing capacitor...which changed the working frequency..which will effect the dc voltage  output , look at the feequncy..i forced the ic the produce waveform just fed 12vdc to pin7 ground to sensing resistor since it is always hooked to ground...got this wave form ...that is bad ..it cant be 1khz no way

@Coulomb

@BritishRacingGreen

 

20240624_183410.jpg

20240624_183432.jpg

You are on to something , keep us informed 👌

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Its confusing to me that the second Sunon schematic says "bus soft start part schematic" (partly in English, mostly in Chinese, I used Google Lens to decode), and TX2/U16 is usually the bus soft start circuit (though usually driven with Q6 not Q7).

For a moment I thought that they used the DC bus to transfer power around, with the TX2 circuit merely enforcing a minimum of 150 V, but that can't be right because C69 is only rated at 200 V (unless there is another diode from +150V to BUS+).

Maybe they repurposed the soft start power supply to become the 150 V power supply (driven from the battery), and somehow soft start the bus some other way. That seems unlikely too. Perhaps it's just a copy and paste error.

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11 hours ago, wael_fathe said:

while changing the uc3845 I knocked timing capacitor...which changed the working frequency.. which will affect the dc voltage  output , look at the frequency..

It would be unusual, though not unheard of, for the capacitor to suddenly increase in value, so maybe R6 (825k, a fairly high value; these seem more prone to trouble) has gone high resistance or even open circuit. It might have a dry solder joint, and by knocking the capacitor, you also knocked that resistor's dry joint, or affected the cracked resistor.

Edited by Coulomb
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