Repairing SMPS - DELL 1800MP - Tricky question maybee?? - Page 1
Forum section: electronics / repair

author: Tony.T
author_rank: Regular Contributor
timestamp: May 07, 2015, 01:36:57 pm
content: Phuuh...tried to fix this SwitchingModePowerSupply for dell 1800MP projector.Have to commit something...made a big mistake...sorry..stupid.....Before the mistake.At point A..just after the R37K resistor. it was 10.7V. Not enough. Point B = 175V, Point C = 300VDCThe ML4800 did not start. Tested with a powersupply to feed in 14V...and it started to kick in. (of course the main supply was disconnected...just wanted to test the ic with low voltage..anyway..)Thought that the resistor R37K and R27Kohm might be to high...so i put another resistor in parallell to achieve a little less ohms. Lowered it a little to much. (ashamed).Blew up the 0ohm resistor...started to sparkle ...ml4800 got shorted.After replacement of the 0ohm resistor...and the ML4800 IC. everything seemed ok. All other resistors....even capacitors seemed ok..BUT. At point B...it is still 175V. But at point A...it is 0.8V. Tried to change the R37K resistor...still almost 0 volt.Disconnected the main supply..and feed the IC with 14 volts again with powersupply directly at point A. The IC kicked in again and works.Soo..the questions.1: Why is it that there is 0 volts at point A now...after that I screwed up? ...using the main supply as usual.2: At the first place...can anybody see on the picture ..what dependencies there is that could have made the Point A only having 10.8 Volts?My guess is that the same component..that lowered the voltage to 10.8 instead of 14-15V...now is totally fucked up...and making it to drop to almost 0V. But as i said...first i thought that there is a directly short to ground after Point A. But feeding the circuit with external powersupply with 14V...works.I am totally lost here....

author: tautech
author_rank: Super Contributor
timestamp: May 08, 2015, 04:45:45 am
content: Common SMPS failure is the controller IC's VCC supply cap normally 22-50 uF.Drift in value and ESR, remove and check to confirm.

author: Tony.T
author_rank: Regular Contributor
timestamp: May 08, 2015, 11:55:02 am
content: tautech..Thansks for trying to help me. This one is really tricky.I have attached a new picture. I have desoldered the two capacitors inside the green ring. Value tested ok The small one 100nF. the bigger one less... ESR tested it and also seemed to be ok.Every other cap that has larger value (polarized ones) ...around 22-100uF....seems also be ok with ESR meter.I have painted the green line how the power comes in. At point A now it is 0.8V. before my stupid mistake..it was 10.8V. Here i am lost. BEcause if i put in 14V directly at point A from external PS....the power IC kicks in. But why is the voltage dropping from 170V to almost 0 just over the 37K ohm resistor? when in main supply?... It must depend on something? And there is no bigger caps that is feeding the power IC what i can see .... the only ones that is around that is larger ceramic capacitors...4700nF...and another 450mFi.ve read that there is a voltage supply directly after rectifier that kicks the IC on...and then it feeds from other side...?!!... I have not managed to find the schematic of this board aswell..it is "PA-4291-1D-LF" from LITEON SMPS..Drives my crazy....

author: wraper
author_rank: Unknown
timestamp: May 08, 2015, 12:02:34 pm
content: Quote from: Tony.T on May 08, 2015, 11:55:02 amIn this particular case more concern is about if they are leaky rather than ESR. Could be some faulty diode (low reverse resistance) too.

author: Tony.T
author_rank: Regular Contributor
timestamp: May 08, 2015, 12:10:24 pm
content: wraperOk...that could be after the Power IC kicking in and feeding the gate of the larger mosfet at the bottom... but my concern now is just why i can not get 14V to power IC directly via point C-B-A.Before it was 10.8V.But if i should comment your thing around zener diodes. See the picture. marked them with a green ring...Those 2 zenerdiodes i measured 0.0045V voltage drop...on both side. Unsoldered them....and they were ok...0.5V voltage drop.. Measured without them inserted...and there is something else shortening the tracks. This zenerdiodes is connected to the PFC trace from the power IC. But as i said..this seems to be another issue. The first one is that the PowerIC does not get 14 V directly to its Vcc pin..... the green painted line i have inserted...through 27K and 37k resistor...point c-b to a...

author: wraper
author_rank: Unknown
timestamp: May 08, 2015, 12:54:39 pm
content: Quote from: Tony.T on May 08, 2015, 12:10:24 pmAs the current before PSU is started is pretty low, it won't ever reach 14V if something have increased current flow. What do you mean by power IC? There are mosfets only.Comparing with this schematic, maybe the mosfets have blown gates?

author: Tony.T
author_rank: Regular Contributor
timestamp: May 08, 2015, 01:06:15 pm
content: I meant the ML4800...to its Vcc pin. This is here where i used a external PSU and feed in 14V....to pin 13.Then i could read out ramp signal at pin 7 with my oscilloscope. When the voltage came to 14V.But when i power up the DUT...this SMPS via its main supply...the voltage drops to 0V at point A...from 170V at point B.Before my mistake..it was at 10.8V at point A....not enough for ml4800 to start...as it needs 14V.I have tested the mosfets...and all the pins seems ok....the mosfets are feed via PFC...and PWM pins from ml4800.But it could be the Q4 transistor that is shorted?... but does this affect the VCC pin..the voltage input there??Edit:Well...there was a little fellow transistor..that was totally shorted... green ring....Must change it..... i´ll be bbbbbbbbbaaaaaaackkkkkk!! ;-) O0Im back....the voltage at pin 13 is now 9V.. :-). So back to square 1. Good. Now hunting the reason why it is only 9 and not 14.....Must be some cap where the capacitans is drifting.....

author: wraper
author_rank: Unknown
timestamp: May 08, 2015, 03:26:11 pm
content: Are zeners no longer shorted?

author: SeanB
author_rank: Super Contributor
timestamp: May 08, 2015, 03:32:42 pm
content: Change that 220uF cap and the one next to it. TRhose are the startup caps, and are probably the leaky ones. You will find a trace leading to them from the top side of the board, connected to the power pin.

author: Tony.T
author_rank: Regular Contributor
timestamp: May 08, 2015, 04:12:23 pm
content: hmm.....zenerdiodes still shorted somehow...from pin 14 ...PFC and through 2 zenerdiodes...Replaced 2 caps (220uF 50v...and 100uF 25V)...and one zenerdiode....and another cap at top right hand corner...Still 9 V ...BUT....i also read 9V at the emitter of the NPN transistor....at top left corner...marked with red circle. One can see that there is a trace going to the right and to a via hole.Need to trace it to see where it goes..... but need to eat first...have not eaten anything the whole day .. :-).Have attached pictures to show that components have been replaced (red circle in pic 2015-bla--bla--).... Thinking of replacing a ceramic cap and another zenerdiode..marked with green circle in same pic...

author: Tony.T
author_rank: Regular Contributor
timestamp: May 08, 2015, 06:13:37 pm
content: Found a shorted smd cap.This fellow is connected through a 1AW transistor directly to the gate of the shorted transistor that i have replaced....where it is 9V at the emitter...Thought that the gate is not high enough...and traced the gate to the other side of the board and found this cap shorted.Now next tricky question....for ones that are not experienced...like me :-)What size of capacitor..no marking at all at this shorted fellow. See picture....red circle...Hate those smd caps without markings...Second picture....followed the gate trace all the way to the bad smd cap..As i said....i only get 9 Volts into the ML4800...and it could be that the transistor is not letting through enough....and this cap seems to shorten the circuit..just a little...enough for dropping it from 15V to 9V. The ml4800 needs 14 volts at minimum...15V is ok.

author: tautech
author_rank: Super Contributor
timestamp: May 08, 2015, 06:29:25 pm
content: Most unusual.Remove and recheck.In-circuit tests are not always reliable. I often swap leads to eliminate a pn junction path giving a wrong result.IMHO controller datasheets, that is from as many manufacturers as you can find, are invaluable for "typical applications", often your circuit will match one exactly. Man, can that help fault finding.

author: Tony.T
author_rank: Regular Contributor
timestamp: May 08, 2015, 06:32:05 pm
content: still the small smd cap is shorted. If i just could replace it with a similar....i could continue searching.....but what size???Just measured the gate voltage. 0.8V. At the collector...it was 0.strange...but something else...i removed the original shorted transistor ..MPS 651....with another that I had.... BC237. Could this be the reason? Did not have the same. I also have a bc547. The difference was the pinout. pin 1 collector....pin 2 base...pin 3 emitter. The original had it opposite....pin 3 collector. So i had to turn the transistor 180 degrees...compared to the original. But anyway...is this different NPN transistor the reason for having only 9V?But again...the smd cap is shorted..and i must find a similar value...somehow...SOrry for stupid questions....and maybee stupid mistakes...but hey...im trying :-)

author: tautech
author_rank: Super Contributor
timestamp: May 08, 2015, 06:42:26 pm
content: Quote from: Tony.T on May 08, 2015, 06:32:05 pmTry a value of 10 nF, 0.01 uF.

author: Tony.T
author_rank: Regular Contributor
timestamp: May 08, 2015, 07:23:05 pm
content: damn...it was not shorted...removed the cap...and measured shortage over the pads where the cap was. So...it is something else shorted nearby....pjuuh....

author: ljcarballo
author_rank: Contributor
timestamp: April 26, 2017, 07:26:49 pm
content: Did you manage to repair the source?I have the same problem, in the leg 13 I have 10.9V and I think they are insufficient to power the integrated, I checked the resistors and everything is OK, but in the IN5406 I fall 27V, would it have to have 1.2V? .a greeting¿Lograste reparar la fuente?Yo tengo el mismo problema, en la pata 13 tengo 10,9V y pienso que son insuficientes para alimentar el integrado, he comprobado las resistencias y todo esta OK, pero en el diodo IN5406 me caen 27V, ¿Tendria que tener 1,2V?.Un saludo

author: dicky96
author_rank: Regular Contributor
timestamp: April 27, 2017, 05:25:43 pm
content: This is a very old thread so I am not sure he found the fault.From my somewhat limited experience of SMPS faults it sounds like he was looking for this fault in the wrong area of the circuit, though I have no knowledge of this actual psu, but I do know what is commonly found in these designs.As he points out the ML4800CP will power up when he applies 14V to the Vcc input, but he only has 10V or so on that pin so it can not start up.He does mention at one point... 'i.ve read that there is a voltage supply directly after rectifier that kicks the IC on...and then it feeds from other side...?!!' and that is the thing I think everyone was missing.If you look at the datasheet for ML4800CP you will see that is has a startup current of 200uA and a running current of 5.5mAQuite often what you will find is a high value resistor connected from the +ve of the main smoothing capacitor after the bridge rectifier (approx 350V) - the high value resistor then charges an electrolytic and this is connected to the Vcc pin of the driver IC. When you turn the PSU on, this high value resistor + capacitor give enough voltage to start the driver IC oscillating. However this can only supply the start up current not the running current. So there is usually a diode connected from a sparate secondary on the SMPS transformer which takes over and supplies power to the driver IC once it starts up.Now the fault he was describing is typical of a situation where you get the startup current, but the secondary Vcc supply can not take over due to a fault in the SMPS. This explains why it will poer up if you use a bench PSU to power the driver chip.One of the most common faults that stops the PSU firing up in this situation is a short circuit on one of the secondaries. This can be caused by a short circuit load (try disconnecting the load and see if it fires up) but more often is a short circuit Shottky Diode on one of the secondaries.I would be looking for short circuits on the SMPS outputs.If I didn't find any shorts on the outputs then my next step would be to power the supply up with a 60W 240V light bulb in series with mains live. Then I would use the bench PSU to start the driver ship with the mains applied (via the light bulb) and using my scope I hopefully would be able to fault find as to why it is not running. I would do tis via a mains isolation transformer but if you don't have one you would still be OK as long as your bench power supply has an isolated (floating) outputThe light bulb is there so that if something goes short when you force the driver chip to run (or for example due to a fault the driver IC turns the power Fet ON rather than driving it with PWM) then the worse thing that will happen is the bulb will light up and not something going bang.Hope that helpsRich

author: dicky96
author_rank: Regular Contributor
timestamp: April 27, 2017, 05:29:53 pm
content: Oh and forgot to mention don't connect a scope ground to anywhere on the HT side of the PSU unless you have an isolation transformer!!!

author: gbrettell
author_rank: Contributor
timestamp: April 27, 2017, 08:03:43 pm
content: In my experience with repairing SMPS ... it is typically the capacitors on the secondary @ the output. On a rare occasion it was the small electrolytic cap on the PWM controller feeding the primary. Think of which parts are doing the most 'work' and that is typically where the failure will occur. Of course there are numerous other possible scenarios ... have fun!

author: dicky96
author_rank: Regular Contributor
timestamp: April 27, 2017, 10:16:18 pm
content: Yes that could cause this sort of problme... and if you are really unlucky, short circuit turns in the SPMS transformer

author: dicky96
author_rank: Regular Contributor
timestamp: April 28, 2017, 10:30:25 am
content: Take a look at the circuit diagram on post #5. The following is the correct operation of the PSU.When the PSU is first powered up, the Vcc supply for the ML4800 is as follows:Current flows from the positive end of the bridge rectifier BR1 via R27 (82k) to charge C26 (47uF).When the voltage across C26 reaches 15V the Zener diode D2 clamps the voltage to 15V so it can not rise any further.This voltage is connected to pin 13 Vcc of the ML4800 and is sufficient to start the chip oscillating. The startup current is 200uA but once the chip starts to oscillate the running current is 5.5mA and this starts to discharge C26.With ML4800 running should now produce PWM output from pin 11 of ML4800The PWM output drives the FETs and the power supply starts to runReferring back to the circuit diagram there is a winding on the SMPS transformer marked T2C. The voltage generated in this winding flows via the rectifier D12 to charge C12 (10uF). This voltage feeds the 15V zener D2 via R28 (240R) And again the Zener clamps this to 15v and charges C26 47uF.THIS is the circuit path that keeps the ML4800 running.Startup path R27 -> C26 -> ML4800 pin 13Running path D12 -> C12 -> R28 -> C26 -> ML4800 pin 13Once you understand that (and this is where Tony.T failed) you will realise that R27 can only supply the 15V long enough to get the ML4800 running, then the capacitor C26 will start to discharge, and if D12/R28 don’t take over supplying the running current for ML4800 the Vcc will drop to about 10V and it will stop.So your problem is either1. The ML4800 is faulty and can not drive the power FETs (you pretty much eliminated that by using a bench supply)2. There is a fault in the power FETS themselves – I doubt this as they normally go short circuit when they fail. If you notice from the diagram on post #5 the power FET Q3 is driven from the pwm output on ML4800 pin 11 and power FET Q2 is driven from winding T1B on the transformer. Any problems in this area could stop the power supply from firing up.3. There is some load (probably a short circuit) on the power supply output that prevents it from running. This is very common and what I would check first – check D11A and D11B – these shottky diodes will most likely be in a TO220 style package and look like a power transistor. It is very likely you have a short circuit here.4. L1 & D1 is probably the inductor and 1N5406 you see on your board. In which direction are you reading 27V across the 1N5406 – forward biased or reverse biased? How does the 1N5406 check on a multimeter diode test? L1 & D1 form part of the circuit known as power factor correction. A problem here such as open circuit D1 would also cause the power supply to fail to start in the way you are seeing5. There is another scenario which would stop the psu from starting up. If R27 goes high resistance or open circuit, or alternatively C26, D2, C12, C15 or D12 are leaky or short circuit you will never get the 15V to start ML4800 in the first place. Of these possibilities I would say R27 high value or open circuit is the most likely but you should check them all.Rich

author: dicky96
author_rank: Regular Contributor
timestamp: April 28, 2017, 10:40:33 am
content: CorrectionThat should read:Referring back to the circuit diagram there is a winding on the SMPS transformer marked T2C. The voltage generated in this winding flows via the rectifier D12 to charge C12 (10uF). This voltage feeds the 15V zener D2 via R28 (240R) And again the Zener clamps this to 15v and charges C26 47uF.

author: tautech
author_rank: Super Contributor
timestamp: April 28, 2017, 11:28:38 am
content: @ dicky96Thanks for your clear and concise write up, this is just as most of us experienced with these SMPS see it too.The basic common layouts are quite similar with the IC and its individual peculiarities being the greatest variable in the design.You should properly edit your post, use either Modify at top right or the little box at bottom right of your post to enter the edit window. Then you can delete, copy and paste from your last post to where you want to correct.Try it.

author: dicky96
author_rank: Regular Contributor
timestamp: April 28, 2017, 12:48:24 pm
content: Thanks tautech - I didn't see the 'edit post' button. I 've now corrected the original post and fixed a couple speeling errors as wellI also added scenario 5.

author: ljcarballo
author_rank: Contributor
timestamp: April 28, 2017, 09:02:16 pm
content: We continue to try to repair the source, thank you very much for all the comments that you have put, I have reviewed all the components that reach the leg 13 of the integrated and everything seems correct, my next test is going to be to change the resistance of 37K (when I measured it calculate 5% and was in the range), but now writing this comment, I think that the colors marked 39K and what I measured were 36K2, tomorrow I withdraw and I measure it again, because the lower that value the less tension I go To have in leg 13. The current that is passing is about 4mA. Tomorrow after the tests I say something.Seguimos intentando reparar la fuente, agradezco mucho todos los comentarios que habéis puesto, he revisado todos los componentes que llegan a la pata 13 del integrado y todo parece estar correcto, mi próxima prueba va a ser cambiar la resistencia de 37K (cuando la medí calcule el 5% y estaba en el rango), pero ahora escribiendo este comentario, creo recordar que los colores marcaban 39K y lo que yo medí fueron 36K2, mañana la retiro y la vuelvo a medir fuera , porque cuanto mas baje ese valor menos tensión voy a tener en la pata 13. La corriente que esta pasando son unos 4mA. Mañana después de las pruebas os digo algo.

author: ljcarballo
author_rank: Contributor
timestamp: April 28, 2017, 09:04:12 pm
content: Forgive my English, but it is null, all based on a translator.Perdonar mi ingles, pero es nulo, todo a base de traductor.

author: dicky96
author_rank: Regular Contributor
timestamp: April 29, 2017, 09:42:10 am
content: @ljcarbelloYou are missing the point here mate. If you have 4mA flowing through that resistor then it is more than enough to start the ML4800, which only needs 200uA to start. The startup current path is OK. Your problem is elsewhere because the power supply is not generating the running current for ML4800Have you checked for short circuits on the output of the power supply as I suggested?Rich

author: tautech
author_rank: Super Contributor
timestamp: April 29, 2017, 10:12:03 am
content: Quote from: dicky96 on April 29, 2017, 09:42:10 amYep, that's the bit many don't understand.....the controller might have a start supply but the rest of the SMPS must have no faults for it to start so the run supply can keep the controller going.This is where and external supply to get the controller to a run state so the output waveforms can be checked and confirmed as correct to make the thing work. Don't try this while on mains power or the whole thing might go POP.

author: dicky96
author_rank: Regular Contributor
timestamp: April 29, 2017, 12:35:05 pm
content: @tautechYep that's true mate!! At least we have the required emoticon lol

author: ljcarballo
author_rank: Contributor
timestamp: April 29, 2017, 01:01:12 pm
content: Everything remains the same, I have placed a resistance of 39K but the voltage is still 10.9V, I have to start over because there is something I am jumping.I have reviewed the two schottky diodes on plate and they are fine, there is no short. The post 5 circuit is a standard application for the LM4800, I will try to upload a small reverse engineering scheme, as well as a couple of photographs to see where the transformer and the schottky diodes are.Todo sigue igual, he colocado una resistencia de 39K pero el voltaje sigue siendo 10,9V, tengo que empezar de nuevo porque hay algo que me estoy saltando.He revisado los dos diodos schottky en placa y están bien, no hay ningún corto. El circuito del post 5 es una aplicación estándar para el LM4800, voy a intentar subir un pequeño esquema de ingeniería inversa, así como un par de fotografías para ver donde se encuentra el trasformador y los diodos schottky.

author: dicky96
author_rank: Regular Contributor
timestamp: April 29, 2017, 03:18:58 pm
content: @ljcarballoAhh that's good you tested the schottky diodes. Knowing there is no short circuit on the power supply output is a good start.OK let's see if we can help you further. What test equipment do you have available?Do you have an oscilloscope? If so is it a mains one or a portable battery one?You said you have a bench power supply. What are it's capabilities (or what make/model so I can look them up)? Is it a single or dual supply?If it is a variable dual supply is it something like 30v-0-30v or does it have two independant variable supplies 0-30V 0-30V. Alternatively do you have two variable voltage power supplies available?I don't suppose you have a mains isolation transformer? That would really help but we can work without one.Also could you measure some voltages please.... place your negative meter lead on the negative end of the big 450V electrolytic capacitor, Now measure the voltage at both ends of the large 1N5406 diode. What do you see?Rich

author: ljcarballo
author_rank: Contributor
timestamp: April 29, 2017, 08:33:01 pm
content: I have a meter and oscilloscope, I have two power supplies, the one I use is ZXY6005S, the other I have to repair the intensity regulation, dual source I do not have, the isolation transformer is a project that I have in mind since I recover two transformers Same as an amplifier and I want to prepare something.The first voltage is 315V and the second voltage is 287VTengo polímetro y osciloscopio, tengo dos fuentes de alimentación, la que suelo usar es ZXY6005S, en la otra tengo que reparar la regulación de intensidad, fuente dual no tengo, el trasformador de aislamiento es un proyecto que tengo en mente ya que recupere dos trasformadores iguales de un amplificador y quiero preparar algo.El primer voltaje es 315V y el segundo 287V

author: ljcarballo
author_rank: Contributor
timestamp: April 29, 2017, 08:35:56 pm
content: The two images are of the voltage falling on the diode.Las dos imágenes son de la tensión que cae en el diodo.

author: dicky96
author_rank: Regular Contributor
timestamp: April 29, 2017, 09:10:09 pm
content: OK that sounds good amount of equipment - it is quite late in the evening here now, will reply in detail in the morningRichard

author: ljcarballo
author_rank: Contributor
timestamp: April 29, 2017, 10:16:46 pm
content: In post 29 in the image of the scheme I have noticed that the "P13" that goes below the resistance of 39K has been cut offEn el post 29 en la imagen del esquema me he fijado que ha quedado cortada la "P13" que va debajo de la resistencia de 39K.

author: dicky96
author_rank: Regular Contributor
timestamp: April 30, 2017, 05:23:48 pm
content: Ahh..... today was definitely a day for the beach here in Gran Canaria!OK let's do some work. The photo of your Fluke - I assume that waveform in on the anode of the !N5106 diode? It is 100Hz so is the full wave rectified output from the bridge rectifier. How are you powering the SMPS in this photo? Directly from mains supply or from the output of an AC transformer?Here are a few things i would like you to try. When you connect the SMPS to the 220V mains supply, what voltage do you read across the 100uF 450V electrolytic capacitor?If you then switch off the mains supply what happens to the voltage on the 450V capacitor? Does it discharge rapidly or slowly?Once the 450V capacitor is fully discharged connect your variable power supply as follow:Negative of bench supply to negative end of the 450V capacitor.Positive of bench supply to a 220R or 270R resistor.The other end of the 220R/270RE resistor to pin 13 on ML4800.Nowwithout any 220V mains voltage supply to the SMPS, turn on your variable voltage supply and bring the voltage up to 15V or just over.Use your oscilloscope and have a look at pins 11 and 12 of ML4800. What do you see there?Does the SMPS have 2 power FETs like the example circuit diagram or just one? With the oscilloscope what do you see on the Gate pin of the Power FET(s)?Reply back once you have done that.Oh.... and could you tell me is your ZXY6005 powered from a step down transformer like this video?or do you have it connected in some other way?CheersRich

author: ljcarballo
author_rank: Contributor
timestamp: May 01, 2017, 11:25:40 am
content: OK let's do some work. The photo of your Fluke - I assume that waveform in on the anode of the !N5106 diode? It is 100Hz so is the full wave rectified output from the bridge rectifier. How are you powering the SMPS in this photo? Directly from mains supply or from the output of an AC transformer?The image of the fluke are the tips in parallel with the diode IN5106Here are a few things i would like you to try. When you connect the SMPS to the 220V mains supply, what voltage do you read across the 100uF 450V electrolytic capacitor?The voltage is: 315VIf you then switch off the mains supply what happens to the voltage on the 450V capacitor? Does it discharge rapidly or slowly?I would say slowly, from 315V to 10V it takes 45sUse your oscilloscope and have a look at pins 11 and 12 of ML4800. What do you see there?Does the SMPS have 2 power FETs like the example circuit diagram or just one? With the oscilloscope what do you see on the Gate pin of the Power FET(s)?The oscilloscope does not mark anything either on leg 11 or 12 and on the two doors of the mofet transistors, either, the power supply is consuming 10mA (I send you an imageDoes the SMPS have 2 power FETs like the example circuit diagram or just one? With the oscilloscope what do you see on the Gate pin of the Power FET(s)?Nothing, nor when I feed with 15V the ML4800, nor when I put the mains voltage (230V)In this assembly the ML4800 has two mofet, although at the output has three voltages (second photograph)Oh.... and could you tell me is your ZXY6005 powered from a step down transformer like this video?or do you have it connected in some other way?My ZXY6005S I have it connected to a switched power supply of 24V and 4.5A in one of the pictures can be seen.The conclusion I get is that the ML4800 does not work and I will have to replace it and start over to check everything. What do you think?Enjoy everything you can from the beach, here in Valladolid is very cold for water.La imagen del fluke son las puntas en paralelo con el diodo IN5106El voltaje es de: 315VYo diría que lentamente, de 315V a 10V tarda 45sEl osciloscopio no marca nada ni en la pata 11 ni 12 y en las dos puertas de los transistores mofet, tampoco, la fuente de alimentación esta consumiendo 10mA (te mando una imagen)Nada, ni cuando alimento con 15V el ML4800, ni cuando meto la tensión de red(230V)En este montaje el ML4800 tiene dos mofet, aunque a la salida tiene tres tensiones (segunda fotografia)Mi ZXY6005S la tengo conectada a una fuente de alimentación conmutada de 24V y 4,5A en una de las fotografías se puede ver.A la conclusión que llego es que el ML4800 no funciona y tendré que sustituirlo y empezar otra vez a comprobar todo. ¿Qué opinas tu?Disfruta todo lo que puedas de la playa, aquí en Valladolid hace mucho frio para el agua.

author: dicky96
author_rank: Regular Contributor
timestamp: May 01, 2017, 01:52:44 pm
content: OK if the ML4800 definitely has around 15V on pin 13 when feeding from your bench power supply via the 220R resistor, and you say it is drawing about 10mA which is about correct - some of those mA will be flowing through the 15V zener diode - then one likely possibility is you have a faulty ML4800Let's just be sure of a few things before condemning it. With the ML4800 powered from your 15v SUPPLY...1. There is definitely 15V measured on pin 13?2. There is definitely no signal on pin 11 or 12?3. Do you see any signal or voltage on pins 5,7,8 when powering the ML4800 with 15V?4. Is there a short circuit to ground on pins 5,7 or 8?RichrICH

author: ljcarballo
author_rank: Contributor
timestamp: May 01, 2017, 08:54:52 pm
content: With 17V powering the ML4800 and consuming 10mA are the measures you asked me:1. On pin 13, 14.820V2. On pin 11 and 12 with respect to 0V we have nothing.3. On pin 5, 0V; On pin 7, 2.632V; On pin 8, 0V.4. There is no short circuit on pins 5.7 and 8 with respect to 0Va greetingCon 17V alimentando el ML4800 y consumiendo 10mA están son las medidas que me pedias:1. En el pin 13, 14,820V2. En el pin 11 y 12 con respecto a 0V no tenemos nada.3. En el pin 5, 0V; en el pin 7, 2,632V; en el pin 8, 0V.4. No hay cortocircuito en los pines 5,7 y 8 con respecto a 0VUn saludo

author: ljcarballo
author_rank: Contributor
timestamp: May 01, 2017, 09:29:10 pm
content: I leave the block diagram of the ML4800.Dejo el diagrama de bloques del ML4800.

author: dicky96
author_rank: Regular Contributor
timestamp: May 02, 2017, 01:03:43 pm
content: I think under those conditions the ML4800 should produce a PWM output on pin 11 so I would try replacing the ML4800When you fit the replacement I would power up the Dell SMPS with a 60W light bulb or similar in series with the mains. Don't connect a load to the power supply the first time you try it, and see if there is any output voltage.I actually made little a test unit with light bulb holder, mains plug, switch and mains socket.The switch I can either set to 'Limit' which supplies power to the device under test via the light bulb or 'Mains' which shorts out the bulb and supplies power directly. I keep a few different bulbs of different wattage - the one I use mostly is a 220V 48W halogen bulbAt least if you connect it that way nothing bad will happen - worse case is the bulb will light upThis is a good way to test unknown condition mains powered devices without the chance of something going BANG!Rich

author: tautech
author_rank: Super Contributor
timestamp: May 02, 2017, 08:11:29 pm
content: We know those bulb testers on the forum as Dim Bulb testers. Google returns an explanation of them and their usage.Handy bit of kit and I use one every time there is a chance of releasing magic smoke.They take little effort to cobble one together.Here's mine and link below to an old thread with description of usage.https://www.eevblog.com/forum/repair/suggested-for-a-sticky-part-one-comments-or-additions-please/msg470686/#msg470686

author: ljcarballo
author_rank: Contributor
timestamp: May 02, 2017, 10:16:42 pm
content: Thanks for that infinite patience that you have had with me, when I try something for the first time I also connect it to a circuit like the one you have drawn to me, it seems very practical and I avoid that if you jump the differential, my wife gets mad at me, ML4800 and I will change it to see what happens, the only thing that I have finished the rest and now it will take a little longer in the repair due to lack of time, as soon as I realize I will comment the results here. a greetingGracias por esa paciencia infinita que habéis tenido conmigo, cuando pruebo algo por primera vez también lo conecto a un circuito como el que me habéis dibujado, me parece muy practico y evito que si salta el diferencial mi mujer se cabree conmigo, voy a pedir el ML4800 y lo voy a cambiar a ver que sucede, lo único que se me ha acabado el descanso y ahora tardare un poco mas en la reparación por falta de tiempo, en cuanto lo realice comentare por aquí los resultados. Un saludo

author: ljcarballo
author_rank: Contributor
timestamp: May 07, 2017, 10:40:58 pm
content: I have already removed the ML4800 now waiting to receive the spare and try to see that such.Ya he quitado el LM4800 ahora a la espera de recibir el repuesto y probar a ver que tal.

author: ljcarballo
author_rank: Contributor
timestamp: May 15, 2017, 09:00:57 pm
content: Bad news, already change the integrated, and everything remains the same, I still have the 10.9 V in the leg 13. I will do some reverse engineering to see that it matches the typical scheme that is in the message 5.Malas noticias, ya cambie el integrado, y todo sigue igual, sigo teniendo los 10,9 V en la pata 13. Voy a hacer un poco de ingeniería inversa a ver que coincide con el esquema típico que esta en el mensaje 5.

author: newtechnology
author_rank: Newbie
timestamp: July 30, 2018, 10:53:55 am
content: Hi this theme is very oldi have problem with same power supplyi read all and make many opitFirst need to work this power supply close conection for plug with name switch or solder two wireSecond need make load on 5v line if this two steps not make power not begin . i make load with 5w 12v lamp on 5 v lineand power work fine

author: ljcarballo
author_rank: Contributor
timestamp: July 31, 2018, 08:40:02 am
content: I could not solve it, the device belonged to a friend and I only had the source of feed, I asked the rest to see if having consumption behaved differently, but I bought another equipment and abandoned that and I did not leave it for see if I could solve it, a greeting and thanks for your response.Yo no lo pude solucionar, el aparato era de un amigo y solo tenia la fuente de alimentación, le pedí el resto a ver si teniendo consumo se comportaba de otra forma, pero se compro otro equipo y abandono ese y ya no me lo dejo para ver si podía solucionarlo, un saludo y gracias por tu respuesta.