Bosch 36v Batter Charger Repair Advice

[ar0311]

Hi Guys

I've been working on repairing a Bosch 36v battery charger CV 3640 AL for a little while as a bit of practise but have hit a bit of a brickwall so to speak and would appreciate any tips from those more experienced.

I've followed directions on a post on the web that suggested these units fail due to a blown 180k startup resistor next to the main filter cap. It was indeed open and has since been replaced along with a few other 2.2k's that seemed to get warm. Also replaced the caps on the LV side. I've tested most of the passive gear for shorts etc although i may have missed something.

The issue I'm seeing is I'm seeing the 330VDC across the main xformer, and on the secondary side obviously nothing as its not switching. I'm getting 3-5v AC on the vcc of the PWM chip and optocoupler on the secondary side?

EDIT: Probed on LoZ mode and theres nothing on those pins, which is a little more sane.

The main issue for this board is theres a thick varnish layer over most of it, makes it difficult to read numbers off the IC's. The IC to the left of the hole (left of the xformer is the optocoupler. I think the one below the hole is the PWM but i cant read the partnumber.

Any ideas where to start looking?

[ar0311]

Ok... bear with me!

I traced the vcc on the PWM IC (UC384) and found there was only about 0.3v on it. Switched off the power, measured 45ohms between vcc and gnd. Figured that was screwey, removed the IC to see if I cleared it and POP! went the fuse.

Is it worth throwing a new UC384 in? And anyone can shed some light on why I somehow created a s/c on the 240v side to blow the fuse?

Oh, and resistance between vcc pad and gnd pad went to 4-5k after removing the IC.

[coromonadalix]

clean the ics markings with acetone and give us the numbers,  if we dont have any brand ic's and numbers on them to work with ... you wont get any much help

[ar0311]

OK the PWM is a UC3842BNG. The secondary rectifier is a STTH2003CT (tested OK out of circuit).

Main switching FET is STP6NK90Z which appears to be shorted. Strange though this happened when I pulled the PWM, as I've had it powered up/down numerous times changing out caps and resistors!

...and since the fuse popped I've found two of the bridge rectifier diodes are shorted! They were fine before I pulled the PWM and powered it up.

[ar0311]

Anyone know where to grab leaded glass fuses in Sydney?

Type F T2.5AL250VP (as picture)

[ar0311]

OK I have fixed this, for anyone that may come across a dead one of these here's what I needed to do in the end:

Re-capped all electrolytics
Replaced switching MOSFET
Replaced UC384 PWM controller
Replaced 180k startup resistor near mains filter cap (was open and it is a common failure point on these units apparently)
Replaced both 4w 2.2k resistors (still read ok but were burn marks on board)

Also replaced all 4 bridge rectifier diodes after the fuse blew and sent two open. They tested fine at the beginning of the repair though.
And I found the leaded glass fuses at Wagners on Parra Rd

[sg1009]

I wanted to thank the community and the contributors for helping me fix my charger.

I started by desoldering the relay and the transformer. Both seem fine.
Checked all large diodes. Fine.
Found this forum.
Checked the 180k resistor - open circuit. Replaced with 3w version. Still not working.
Replaced STTH2003CT. No better.
Replaced STP6NK90Z. No better.
Replaced UC3842BNG (8 pin IC). BANG. Fuse blows. Takes out 2 of the diodes near the fuse. Very strange.
Replaced the fuse with a fuse holder off some scrap board I have so I can swap the fuse out easily.
Replaced the diodes. BANG again.
Checked the STP6NK90Z and it's shorted.
Put the old STP6NK90Z back in and replaced the 2 diodes + new fuse. We have a working charger!!!!

Hope this helps people out there.

[cj_hobby]

Im going to pick up this thread purely because it has people with relevant hardware, even though I think it is the battery that I need to repair here (rather than the CV 3620 AL charger from 2019).

I have a battery which gives a red overheat warning whenever you plug it in to the charger, even though it works ok and reports 2 (of 3) battery lights, and has never got hot. My initial assumption was that the thermistor has failed, but Im struggling to work out what to check since I dont have a good/working device to compare with. There is some information on google for repair, but its pretty useless tbh, hence I thought I would add a bit more information here and hopefully get some advice on next steps please .

When you split the middle pins of the battery you have negative on one side, and and I think the thermistor connection on the other, and it took me a while to spot the blank/filler/plastic on one side of the charger pin (hence the two metal prongs on the battery are not the same). I measure this 'thermistor' connection as 99.8kΩ to negative terminal (though that's without disconnecting the thermisor from the circuit which I know could be flawed).

What should the connection read, and is it possible to get a connection without desoldering the thermistor? Or is the connection to the battery more complex than just a 'resistor' check?

[CaptDon]

Wow, going to low-Z mode where there is a potential for 330 volts (assuming it suddenly appeared do to a loose connection etc.) is really dangerous to the scope!!