Bosch AL2215CV charger fix

[momaka]

Re: Bosch AL2215CV charger fix

Thanks again Momaka for your insights and helping out! I will give the repair a go and see how it goes, hope I can get the required parts. I need that drill going!

No problems.
It really is just a matter of finding the right value resistors... or resistors that you can combine in series or parallel to get the right values.
If you can't find any parts locally, see if there are any electronics repair shops near you and ask if they have any broken PC ATX PSUs or LCD monitor power boards. Chances are, you might find most parts on one. The MOSFET parameters for this PSU are not too critical, just as long as the voltage ratings are more or less the same.

Once you fit all the new parts and are ready to test, make sure to use the series incandescent bulb trick. That way, if something is still bad, it should save most or all of your new parts from getting damaged/burned/blown.

[Erdist]

Re: Bosch AL2215CV charger fix

Thanks again Momaka for your insights and helping out! I will give the repair a go and see how it goes, hope I can get the required parts. I need that drill going!

[momaka]

Re: Bosch AL2215CV charger fix

- on the schematics only R6 is in the 3 ohm range (3.6), the burnt resistor could possibly be 3 ohm with 1% tolerance, but confused about the location of that black band. Also the slot is marked as R5 on the board, which is not matching with the schematics. So perhaps go for 3.6?

Yeah, probably anything in the range of 3 to 4.7 Ohms will work... or at least make the PSU try to turn On.
This resistor is used for current sensing, so higher value means it will give more negative feedback, so the PSU may self-limit the power faster... which might be desirable, given that it likes to blow up. Lower resistor = more power allowed by the PSU.

- Right after that, comes F3NK80Z (V6 on the schematics, V5 on the board)

LOL.
Yeah, looks like the schematics are more or less accurate, but the designators aren't. Not a big deal, I suppose, as long as we say explicitly which part we are talking about so we don't get confused.

- then comes R5 on the schematics with 22k ohm, and it looks like it is 39k in the board. Seems like a significant difference.

Not a big deal either.
39K will give about 12.76V max (with a 240V AC line input) at the Gate of the MOSFET, which is OK, since the F3NK80Z is rated for +/-30V V_gs.

-followed by R7 in the schematics with 30 ohms, and on the board (also damaged) looks like it is 30.1k with 1%.

I don't think 30.1 KOhms makes sense for that position. In fact, I'm not even sure why they even have a resistor there. Most 2-transistor circuits I've seen connect the Gate of the MOSFET directly to the small BJT's Collector. That way, when the BJT turns On, the MOSFET Gate is driven to ground and that makes the MOSFET turn Off. If you use 30.1K, that MOSFET may never turn Off properly or make the PSU work only in self-limiting, thus grossly overshooting voltage on the output... or worse - blow up again. The bands also seem to indicate 30 Ohms from your picture. I see Orange, Black, Brown (should be Black, though), Gold, and Brown again. In a 5-band color code, first 3 bands are the digits, 4th is the multiplier, and 5th is the tolerance. So the above should read 300 with the multiplier being 0.1 (Gold)... i.e. 300 x 0.1 = 30 Ohms. And last band, of course, is for 1% tolerance.

With that said, again I don't understand why they even have that resistor there. Just as a reference, here are a few 2-transistor 5VSB circuits from ATX PSUs, so you can see and compare how similar they are and what they did different:
https://www.badcaps.net/forum/attach...1&d=1578459617
https://www.badcaps.net/forum/attach...0&d=1451693563
https://www.badcaps.net/forum/attach...9&d=1443215464

[Erdist]

Re: Bosch AL2215CV charger fix

Momaka, you are a champion! Thanks very much for your help. It starts to make a little sense now, here's what I think looks to be the situation and the reason for my confusion:

- on the schematics only R6 is in the 3 ohm range (3.6), the burnt resistor could possibly be 3 ohm with 1% tolerance, but confused about the location of that black band. Also the slot is marked as R5 on the board, which is not matching with the schematics. So perhaps go for 3.6?

- Right after that, comes F3NK80Z (V6 on the schematics, V5 on the board)

- then comes R5 on the schematics with 22k ohm, and it looks like it is 39k in the board. Seems like a significant difference.

-followed by R7 in the schematics with 30 ohms, and on the board (also damaged) looks like it is 30.1k with 1%.

Do I understand it right?

[momaka]

Re: Bosch AL2215CV charger fix

Oh, and regarding R5 value... I think 22 KOhms is actually right, because that should provide about 6.76V on the Gate of the MOSFET (just do a voltage divider between R3, R4, and R5 and you will see that in order to get a high enough voltage to turn on the MOSFET, R5 must be at least a few 10's of KOhms.)

Also, I just noticed my post from 2019... and yeah, this 2-transistor self-oscillating circuit does not look very well designed. Heck, the whole PCB looks very cheaply made an separation between adjacent HV traces not good at all.

*EDIT*
When I was mentioning R3, R4, and R5, I was referring to this schematic posted by DannyX:
https://www.badcaps.net/forum/attach...8&d=1547107967

Looks like that R5 designator is not referring to the same resistor as the one on your board. The one on yours (behind the MOSFET that connects the MOSFET's Source to primary-side ground) should be a low-value resistor: 3 Ohms sounds about right for that. Make sure you use fusible flame-proof (Metal Oxide / MOX ) resistor. If you use Carbon film, it may catch fire if it fails again. And for the resistor in front of the MOSFET, 20-30 KOhms will probably work fine. Yours looks like 39 KOhms (orange, white, black, red, brown - 5-band code for 39K 1%.) And the one above it that connects MOSFET's Gate pin to NPN BJT's Collector pin - 30 Ohms seems like an accurate value. The schematic posted by DannyX refers to that resistor as R7, and it is indeed showing as 30 Ohms.

[Erdist]

Re: Bosch AL2215CV charger fix

Thanks momaka. It looks like there is a miniature crack on the conformal coating between the first and second diode, so good idea to check!

[momaka]

Re: Bosch AL2215CV charger fix

I cannot seem to find the one you are referring at. The others look ok to me. Any chance you could highlight it on one of the photos for me? Thanks!

Sure.
Look in the lower-left corner of this picture:
https://www.badcaps.net/forum/attach...2&d=1611786894
See the 4 diodes between the transformer and input filter choke (located right next to a blue safety Y2 cap too)? One of them (the 2nd one from the bottom up) appears dented and lead possibly pulled out. I would suggest to remove it and make sure it's not reading O/C. The diodes look like they might have ran a bit hot too, so maybe not a bad idea to check them all anyways.

[Erdist]

Re: Bosch AL2215CV charger fix

One of the diodes in the bridge rectifier looks physically damaged too (possibly lead broken or pulled out.)

I cannot seem to find the one you are referring at. The others look ok to me. Any chance you could highlight it on one of the photos for me? Thanks!

[Erdist]

Re: Bosch AL2215CV charger fix

Yeah, some close-ups of that area would be great (like in the 4th picture of my original post).

Attached more photos. Taking out that burned electrode was my inexperienced butcher work.🙄

Thank you gentlemen for your help so far, you guys rock!

[Erdist]

Re: Bosch AL2215CV charger fix

there is another burned resistor there above it

I see which one you are referring to. You've got sharp eyes! Thanks for pointing it out

[Erdist]

Re: Bosch AL2215CV charger fix

I'd say the resistor should be 30 ohms, as the first band to the right looks orange to me and it also goes with what I was talking about in the thread....it's been a while, so I can't remember exactly unfortunately...

To be honest they do look orange to me too, both on yours and the factory one too. And having the black band in the middle would suggest to me that they are not kOhm? On the factory resistor the second stripe looks almost completely missing, if it was there in the first place it is hard to tell. Could it be only 3 ohms? Your's has a blue/silver line as well after the black, that I can't decipher. Enlarging from your photo:

[momaka]

Re: Bosch AL2215CV charger fix

One of the diodes in the bridge rectifier looks physically damaged too (possibly lead broken or pulled out.)

[Dannyx]

Re: Bosch AL2215CV charger fix

Yeah, some close-ups of that area would be great (like in the 4th picture of my original post).

[petehall347]

Re: Bosch AL2215CV charger fix

I also have a blown resistor in my Bosch AL2215 CV charger, and hope you guys can help out, because I have to admit that knowledge about electronics is zero. Nevertheless I have to do the repair myself, so please be patient if I ask something obvious.

It looks like the burned out resistor is the same as on Dannyx photo, however on my circuit board (1607502155) it is marked as R5.

According to the schematics that he posted R5 is supposed to be 22k Ohm. However using resistor colour coding on the resistor that he has in that spot it looks like that it is only 22 Ohms. Unfortunately the original resistor is difficult to read too.

Any help is much appreciated!

there is another burned resistor there above it

[Dannyx]

Re: Bosch AL2215CV charger fix

I'd say the resistor should be 30 ohms, as the first band to the right looks orange to me and it also goes with what I was talking about in the thread....it's been a while, so I can't remember exactly unfortunately...

[Erdist]

Re: Bosch AL2215CV charger fix

I also have a blown resistor in my Bosch AL2215 CV charger, and hope you guys can help out, because I have to admit that knowledge about electronics is zero. Nevertheless I have to do the repair myself, so please be patient if I ask something obvious.

It looks like the burned out resistor is the same as on Dannyx photo, however on my circuit board (1607502155) it is marked as R5.

According to the schematics that he posted R5 is supposed to be 22k Ohm. However using resistor colour coding on the resistor that he has in that spot it looks like that it is only 22 Ohms. Unfortunately the original resistor is difficult to read too.

Any help is much appreciated!

[llonen]

Re: Bosch AL2215CV charger fix

Looking over the component side of the board it is clear tome that there are still numerous bad solder joints.

[Dannyx]

Re: Bosch AL2215CV charger fix

To me it is not clear how you combined the two resistors in R7 (on the picture R6) to reach 30 Ohms.
When I check the color code, the first Braun, Red, Black brings 12 Ohms. But how to reach 30 Ohms with the second one? With the colors on the resistor I cannot get 18 Ohms.
So please help.

Now that I look at the pictures myself, the colors indeed make no sense and I can't remember what I did there after so long. As I was reading my original post, I thought I combined two 15ohm resistors in series to get 30ohms (didn't explain it in detail myself), but the colors don't match and they're also different between the two....still, the schematic stands, so do whatever it takes to have 30ohms there.

[gvb]

Re: Bosch AL2215CV charger fix

To me it is not clear how you combined the two resistors in R7 (on the picture R6) to reach 30 Ohms.
When I check the color code, the first Braun, Red, Black brings 12 Ohms. But how to reach 30 Ohms with the second one? With the colors on the resistor I cannot get 18 Ohms.
So please help.

[momaka]

Re: Bosch AL2215CV charger fix

C5 kills the self-limiting deal...

I don't know if it's just C5.
C3 may be partially responsible as well. Part of the "feedback" voltage rise from R6 will get coupled through it and slow down the turn Off time on the Gate.

I think it may also be a better idea if R5 was instead replaced with a Zener diode and connected directly to hot ground (to protect the MOSFET Gate better).

Then there is the whole base-driver circuit of U1 and U2 for the smaller transistor...
1) Ideally, there should be a resistor between V5 Base and U1/U2 Emitters to limit current.
2) A cap between hot ground and V8 cathode would provide a more stable voltage to U1/U2 Collectors.
3) The parallel 4007 diode with U1/U2 C-E junctions will likely "eat" some of the turn-On "feedback" coupled through C5.

All in all, it looks like a barely stable design to me. Probably just better to take a Deer/L&C/Allied 2-transistor 5VSB circuit and copy it. They run quite stable after a recap (but they do have a "critical" cap).