Mastervolt Chargemaster 12/35-3 Charger - Failed repair - erratic output

[sententia]

Hello everyone,

This charger had the bridge rectifier and mosfet (in red rectangle) shorted, so i replaced those and the main input filter caps as they were about 20% down of their capacitance.

I thought the charger was working good but after some time of being switched on the charger output high voltages around 20V and gets unstable. It detects the high voltage output and restarts. The heatsink that has the bridge rectifier and mosfet gets hot without any load. Although i haven't managed to find which of the parts on the heatsink is produced the high temp. Also the 2x 51K 2w resistors get about 55c degrees and all the area around that gets quite hot. The voltage on the main filter caps is steady around 180V.

Now i removed some parts to check them and put them back in the charger has the problem almost straight away upon power on.

Any ideas of how to troubleshoot this problem are very appreciated!

Thank you!

Please ask for any more info you may need!

P.S. Mosfet is a SPP20N60C3

[CapLeaker]

Re: Mastervolt Chargemaster 12/35-3 Charger - Failed repair - erratic output

I'd be looking at the feedback circuit, cold solders on the secondary, any glue that got conductive, corrosion, etc...
Try heating things up with a hair dryer and see if you can make it act up faster, while monitoring the output with an oscilloscope.

On your last picture the 2 smd caps don't look that good. Replace those for starters. Clean / replace the opto in front of them too. Clean the whole area. You may have to remove. Some components.

[sententia]

Re: Mastervolt Chargemaster 12/35-3 Charger - Failed repair - erratic output

I have a difficulty identifying the feedback circuit.

On the first picture i have marked the track of PIN 2 which is the feeback of the 2845B ic on the botton side. It does not connect to the opto mentioned i think. The vertical board now has a TL494 and there is a TL431C as well there. I cannot understand which is for standby circuit and for main charger.

This power supply has a standby circuit which operates until power button is pressed and the relay closes.

Now those capacitors look like this because i have remove the 220uf one to test it and putting it back on looks like that ..... The 220uf tested good, as the red one (MKP i think) 22n 630V next to it. I did not remove/test the 100uf one but on board i get much more that 100uf.... These caps are low ESR 25V 5000h. The small one is 2000h.

If by clean you mean the whitish foggy thing on board its the protective material that is on the entire board. It is extremely difficult to remove (and test components) and the white finish appears after isopropyl alcohol is applied to make it a bit softer.

Thank you!

[CapLeaker]

Re: Mastervolt Chargemaster 12/35-3 Charger - Failed repair - erratic output

start to heat things up in there and see if you can "make" it act up.

[sententia]

Re: Mastervolt Chargemaster 12/35-3 Charger - Failed repair - erratic output

After removing some parts for testing, including those caps, and putting them back in the charger goes straight away to 20V.

So far i have tested the parts marked in the photo and quite a few resistors at the bottom of the pcb. Only the Y capacitor seems a bit off only by my "transistor tester" if i measure it with the DMM capacitance it measures ok, but i doubt that it is causing the problem. The are another 2x TL431 marked in the photo. I still haven't distinguished which parts are from which circuit.

Thanks capleeker for guidance!

[CapLeaker]

Re: Mastervolt Chargemaster 12/35-3 Charger - Failed repair - erratic output

When you test the output, do you have a load on it? Oh, I forgot to mention something. Sometimes a resistor changes it's value (usually it either goes higher in the ohms reading or open). Make sure the resistors are within spec.

In front of that little board (bottom left) there are 2 more optos and some caps. Did you check these?

When you monitor the output, is it stable for a while, then goes erratic until it shuts off? Then cool down for a while until it will start again and same thing again?

[sententia]

Re: Mastervolt Chargemaster 12/35-3 Charger - Failed repair - erratic output

ooops i didn't post my previous message ......

I do use my variable current dummy load to test the charger, however only on 1 out of 3 channels. The charger can be used as a power supply on "FLOAT" mode where output voltage is 13.25V.

In front of the vertical board i have tested the two caps and both optos. All tested good.

Now about the resistors i measured. Some have normal code "51R0" etc and some have coding of "01B". I did check measurements compared to marking only for the first ones as i see the "01B" marking ones have irrelevant resistance. "69B" for example is 5.11K.

The charger only switches of for 2-3 seconds before going back on and giving 20V.

Anyway at the moment i did put back all the parts tested, except one 100uf capacitor next to the opto which i destroyed it upon removing and replaced it with a FR one.

Strangely now the charger is on for almost an hour and still haven't presented the problem.... hhhhmmmmmm

EDIT: Is it normal that the primary heatsink is getting hot 33c and bridge rectifier and diode rectifiers at 42c without any load??
The charger only draws 15w from 220V at this state though and no current on the output of course....

[sententia]

Re: Mastervolt Chargemaster 12/35-3 Charger - Failed repair - erratic output

Ok it went to 21V....

The transformer is quite hot at 58c, the fet next to it is at 50c, 1 out of 2 TL431 is significantly hotter than the other. I marked the in photo.... if that helps at all!

[CapLeaker]

Re: Mastervolt Chargemaster 12/35-3 Charger - Failed repair - erratic output

Not sure if the heat is normal or not. I think the charger must have something like a cooling fan that takes the heat off the heatsinks. Maybe you have disconnected it. After all it does 35 amps on 3 channels and total power consumption is 575w on 230V. So 15W idle doesn't sound too bad. If the fan runs all the time the heatsinks would be cool like cucumber. Since you have that thing cracked open anyway, I would change all small caps that see heat, like near a heatsink.

Those resistors with the funny marking like 01B (1kohm, so check them again out of circuit) is after the "EIA" marking code. Here is a list:
http://www.talkingelectronics.com/pr...-Markings.html

[sententia]

Re: Mastervolt Chargemaster 12/35-3 Charger - Failed repair - erratic output

The fan does not run at all times. It kicks in when i increase the load to 1A or 1.5A and as soon as i decrease the load it switches off. The charger does have a sensor on the main transformer and on the secondary heatsink.

I have removed all 3 TL431 and did a simple test to check if they produce 2.5V, so they all look OK. However on board one of them gave only 1.9V reference but this could be, i think, because of resistor network or the fact that i used 5V supply to test it...

[sententia]

Re: Mastervolt Chargemaster 12/35-3 Charger - Failed repair - erratic output

So far i replaced all TL431, replaced some caps just in case and tested many many resistors. The only thing that is a bit off is a ceramic 471K 1KV cap (marked in circle in photo) that measures 440pf. I don't know if that can cause the problem.

Also i remembered that the charger operates with just the batteries connected so i started to probe the optos and some other staff on board with safe voltage.
Almost everything i probe give a 50hz signal.

Moreover the charger has 3 different charging states bulk, absorption and float (according to IUoUo algorithm) with different output voltages and current. Does that make the mosfet i replaced controlled by the microprocessor to regulate the output voltages?? Are the feedback circuits monitored by micro or by pwm ics?

This charger and this awkward problem is a nightmare!

[CapLeaker]

Re: Mastervolt Chargemaster 12/35-3 Charger - Failed repair - erratic output

Did you try heating the board up first and see if it goes to over volt protection? I wonder if you could isolate the problem by using one of the other charge outputs and see if it acts up on one or all three outputs. Compare them. To me what it sounds like is that the problem is either a cold solder joint on one of the power rails on the secondary or something is wrong with the feedback circuit.
Intermittent chasing is hard and at time you have to be creative.
The mosfet you replaced has a driver PWM on the gate, on that driver is the feedback circuit, that comes from the secondary back to the primary. Since there is no schematic you would have to find the PWM, pull the data sheet, find the pin for the feedback and trace it. Or go from the secondary, back to the opto to the primary. Key is to measure the charge output constantly (I used a oscilloscope), then I used my hot air station and heated up individual parts until I found an invisible bad solder joint. Each time I heated or cooled the inductor, I could see changes on the output voltage. It was a dual voltage power supply on a Norstar nt5b01 phone system. If you want you can read the thread.

[sententia]

Re: Mastervolt Chargemaster 12/35-3 Charger - Failed repair - erratic output

I read your thread, and just got what you are saying about heating up the board. No i haven't tried that yet, but i will as soon as i put some parts back after some more troubleshooting and shopping for a couple of ceramic caps.

All 3 channels act exactly with voltage output. Anyway in forced float mode they should all give 13.25V but it happens in all modes....

Now what i didn't know is that the mosfet i replaced is driven by a 2PCS01 PFC controller circuit through those 2x big transistors, on the vertical board (check photo). The opto there connects all the way to the opposite corner of the pcb where the other micro is and the communications board. When you say "monitor the charge output" you mean from ic to opto or the gate drive pin?

Also one strange thing i noticed is that i powered up the charger and forgot to place that opto that i had removed for testing. The charger acted exactly the same giving 20V output upon power on.

Thanks capleaker for your help and suggestions!!

[CapLeaker]

Re: Mastervolt Chargemaster 12/35-3 Charger - Failed repair - erratic output

too bad that there isn't a schematic or a block diagram for this thing. With charge output, I meant one of the three 12v output channels. Put it in constant float mode, put a 12 v light bulb on the 12v output, put your oscilloscope on that channel and make it scan real slow, so you can see like 20 or 30 seconds. Start heating and cooling (can of air upside down) things. Once you found the offending part, you will see changes on the oscilloscope.

[sententia]

Re: Mastervolt Chargemaster 12/35-3 Charger - Failed repair - erratic output

I have put everything back together, i had to replace 4 electrolytics that i destroyed while removing them and 1 ceramic 102k 1kv which i replaced with a blue one 102 3kv (i think this one is 20% tolerance compared to 10% of the original ceramic). I redid some soldering connections on board and put it on test with the dummy load at 0.8A.

It has been operating for 10 hours without any problem and steady output.

I used my hot air station at 200c on the bottom side to try and make it act but no difference....

Actually some soldering connections had small cracks (on microscope) and i lean forward that it was indeed a bad soldering or something like that. I will redo the chokes as well to be on the safe side.... I will get some 20w lamps to put some more load on it....

[CapLeaker]

Re: Mastervolt Chargemaster 12/35-3 Charger - Failed repair - erratic output

Hopefully it works now. You have to put the heat on the component side of the PSU. To me your board looks like corrosion. Never the less an intermittent is hard to troubleshoot.

Maybe charge some batteries up and see what happens.

[sententia]

Re: Mastervolt Chargemaster 12/35-3 Charger - Failed repair - erratic output

I have tested the charger with 3x 20w lamps for 10 hours. Now i have it running on batteries for 2 days and no problems...

I come to conclusion that it was a bad soldering problem....

It is also possible that i stressed the vertical board while repairing and flipping over the pcb. I also did the coil and transformer soldering again using lots of flux and new solder.....

Thank you capleaker for input, guidance and help! I really appreciate it!

P.S. I got a heartbeat for a day or so... the charger gave "internal failure" after i put everything inside the enclosure. I turned out that i had the fan disconnected!

[CapLeaker]

Re: Mastervolt Chargemaster 12/35-3 Charger - Failed repair - erratic output

Glad to hear that you got her finally working. A1! I figured that the charger would do a failure of some sort if the fan is disconnected. Been there, done that too... Don't feel bad...

[Randolfo]

Re: Mastervolt Chargemaster 12/35-3 Charger - Failed repair - erratic output

Mr. CapLeaker, If you can help me on a Mastervolt Chargemaster 12 / 35-3, I thank you. The fault is: this stop. In capacitors of 680u / 250V has a voltage of 187Vdc. In the zener ZDB8 has 6.9Vdc and in the pins of the 2845 CI only has 6.9Vdc in the pin 7, I understood that the firing in the 1 does not occur. You can guide me, grateful.

[CapLeaker]

Re: Mastervolt Chargemaster 12/35-3 Charger - Failed repair - erratic output

Check if the UC2845 PWM gets proper VCC voltage so it isn't in under voltage lock out and check the startup cap. I haven't pulled the spec sheet, but if the 6.9V are the VCC for the PWM, then it is too low for it to start.