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Old 02-14-2020, 06:01 AM   #1
ex250
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Default Help with car battery charger HT7715

Hi guys, I have this battery charger that stopped working meanwhile was charging the car battery, now the display didn't work and plugging the charger I only listen a low click noise, like a relay and nothing else.

It's branded as Carrefour, but could be found also as Dunlop charger, 909, Coitech, and posibly many others. I can't find a service manual or schematic to check the board, on the board there is only a text with HRS7715 and a date.

Any ideas?

Thanks in advance!
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Old 02-14-2020, 06:19 AM   #2
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Default Re: Help with car battery charger HT7715

i dont see any vents?
probably the small caps are dried out.
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Old 02-14-2020, 12:28 PM   #3
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Default Re: Help with car battery charger HT7715

Nothing seems damaged, the charger has been barely used.
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Old 02-14-2020, 02:24 PM   #4
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Default Re: Help with car battery charger HT7715

A low clicking noise might suggest the power supply is trying to start, but the startup capacitor is bad or dried out as stj suggested.

A dried out cap won't show any obvious signs of damage.
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Old 02-14-2020, 03:09 PM   #5
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Default Re: Help with car battery charger HT7715

sorry for my ignorance, but witch one is the startup capacitor? black big one? square yellow ones at the AC side? Thanks!
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Old 02-14-2020, 03:36 PM   #6
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Default Re: Help with car battery charger HT7715

C24 in the hot side.
You should also check the small lytics caps in the cold side also.
Did you already check all the diode, rectifiers?
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Old 02-14-2020, 05:01 PM   #7
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Default Re: Help with car battery charger HT7715

Also, there may be some cracked or cold solder joints here? See pic.
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Old 02-14-2020, 05:10 PM   #8
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Default Re: Help with car battery charger HT7715

On the back of the PCB, one of those larger ICs should be the SMPS chip.

If you look at its part number and find the datasheet, it will tell you what the typical VCC startup voltage should be.

Then check C24, the startup cap to see if it is present.
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Old 02-14-2020, 05:23 PM   #9
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Default Re: Help with car battery charger HT7715

BTW, the PCB was made 2010 03 02 so it's 10 years old.

If the startup cap was cheap quality to begin with, I can see it failing/dried out even without much usage.
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Old 02-14-2020, 07:32 PM   #10
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Default Re: Help with car battery charger HT7715

I would check the voltage on these two capacitors, and see if it is stable, that could provide some information as to how the primary is operating.
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Old 02-15-2020, 01:27 AM   #11
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Default Re: Help with car battery charger HT7715

Quote:
Originally Posted by retiredcaps View Post
Also, there may be some cracked or cold solder joints here? See pic.
That one was me after unsoldering the mosfet to check , seemed ok for me. The board is covered with a poor? varnish coat, I don't know how to remove it without damaging nothing, makes readings with the meter be tricky.
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Old 02-15-2020, 01:46 AM   #12
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Default Re: Help with car battery charger HT7715

Quote:
Originally Posted by R_J View Post
I would check the voltage on these two capacitors, and see if it is stable, that could provide some information as to how the primary is operating.
0V on the top and 0,001V on the botton one
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Old 02-15-2020, 06:44 AM   #13
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Default Re: Help with car battery charger HT7715

Quote:
Originally Posted by budm View Post
C24 in the hot side.
You should also check the small lytics caps in the cold side also.
Did you already check all the diode, rectifiers?
Unsolded the C24 and reads 43uF on my tester, is a 47uf35v one, not a enought bad reading to prevent starting, not?
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Old 02-15-2020, 07:01 AM   #14
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Default Re: Help with car battery charger HT7715

Tracing the click noise, seems to be from the bridge big chip, but I don't know how to check it or about the expected readings on each pin. It's a RS606.

Last edited by ex250; 02-15-2020 at 08:20 AM..
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Old 02-15-2020, 01:13 PM   #15
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Default Re: Help with car battery charger HT7715

If you are getting 0 volts on the large cap I asked about, then the primary is not operating, The bridge rectifier is easy to check in diode mode, it is just 4 seperate diodes in one case. I suspect it is ok, if it was shorted the main fuse would have blown.
As for C24, replace it, I have seen the capacity check ok but they can be bad. The ticking you here is the power supply trying to start but shuts down, this can be caused by a bad C24 startup capacitor, it needs to charge up to sustain the VCC voltage for the pwm ic.
You could also have a short in the secondary, so check the dual diode (below the large cap I had circled)

Last edited by R_J; 02-15-2020 at 01:29 PM..
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Old 02-15-2020, 01:39 PM   #16
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Default Re: Help with car battery charger HT7715

Quote:
Originally Posted by ex250 View Post
Unsolded the C24 and reads 43uF on my tester, is a 47uf35v one, not a enought bad reading to prevent starting, not?
While it may be okay with respect to uF, it may not meet it's ESR specifications.

https://www.allaboutcircuits.com/tec...of-capacitors/
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Old 02-15-2020, 01:59 PM   #17
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Default Re: Help with car battery charger HT7715

Quote:
Originally Posted by R_J View Post
If you are getting 0 volts on the large cap I asked about, then the primary is not operating, The bridge rectifier is easy to check in diode mode, it is just 4 seperate diodes in one case. I suspect it is ok, if it was shorted the main fuse would have blown.
As for C24, replace it, I have seen the capacity check ok but they can be bad. The ticking you here is the power supply trying to start but shuts down, this can be caused by a bad C24 startup capacitor, it needs to charge up to sustain the VCC voltage for the pwm ic.
You could also have a short in the secondary, so check the dual diode (below the large cap I had circled)
both big diodes seem to be ok on test, 0,6xx readings and nothing on reverse. Will try with one new cap to see what happens.

The tick is only one time when plugged, not repeated until I disconect and conect again on the AC plug.
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Old 02-15-2020, 02:28 PM   #18
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Default Re: Help with car battery charger HT7715

Quote:
Originally Posted by ex250 View Post
both big diodes seem to be ok on test, 0,6xx readings and nothing on reverse. Will try with one new cap to see what happens.

The tick is only one time when plugged, not repeated until I disconect and conect again on the AC plug.
Well, the click may be from the black relay you have on that board, which means there is power from some where to power the relay.

Last edited by budm; 02-15-2020 at 02:33 PM..
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Old 02-15-2020, 02:45 PM   #19
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Default Re: Help with car battery charger HT7715

Quote:
Originally Posted by budm View Post
Well, the click may be from the black relay you have on that board, which means there is power from some where to power the relay.
Not seems from there, but I can see if there is any values at the relay pins.
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Old 02-15-2020, 02:56 PM   #20
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Default Re: Help with car battery charger HT7715

Nothing relevant on the relay, residual values of 0,002v, the brigge reads 140v in one pair and 132 on the other (230v AC at plug)
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