Fluke Scopemeter 196 yet again

[squigley]

I have a Fluke Scopemeter I salvaged from stuff being thrown out at a place I worked. With the power supply brick attached it would power on for a couple of seconds and then abruptly power off.

I figured that the battery pack was toast, so I opened it up, tested a couple of cells which showed almost zero voltage, and went about rebuilding the pack, using 18650s since they are the same size as the cells that were in the pack.

I stupidly didn't think to check the original pack, to see that it specified 7.2V, and instead built a ~24V pack, (even more stupidly thinking they were 3v cells, instead of 4, and 6x3 = 18V which seemingly matched the 17.5V power supply brick..) Upon connecting it and trying to power on some magic smoke came out.

I initially thought this was the surface mount fuse right near the battery connector (which apparently it was, as the plastic surface became all brittle and has flaked off), but I can see the zig zag track in it, and it still tests as closed/continuity.

I got the service manual, and started tracing the circuit, getting as far as the voltage transistor which supplies the P ASIC, and seeing it's a BC859, looked up the data sheet to find it's a base/collector/emitter pin 1/2/3 standard line up, and the service manual says there is supposed to be at least 3V coming out (or up to 20). I see just over 10V on the emitter pin, but very strangely zero on the collector, so I'm not sure where this is coming from..

As a quick test, in an attempt to identify if it's just the transistor I blew, I shorted the collector and emitter (which should normally be "on" since it's a PNP) using the tip of the probe, just to see if there were any signs of life. The only noticeable result of this is that the Garfield chip (D ASIC?) gets hot enough to give me a 3rd degree burn quite quickly.

I'm pretty sure this means I've buggered the ASIC, at which point it's not worth trying to fix since I don't have the tools/capability/parts to attempt to swap the ASIC.

Suggestions? Should I just put it on ebay saying I've blown up the charging circuit and the ASIC, and let someone else use it for spare other parts, since it has a good case/LCD/leads etc?

[Arhigos]

omg. you cannot just replace ni-mh cells with lion. Lion batteries requires charging controller.

Also, as far as i know, it should work even without battery.  So i guess it was dead at the moment when it was scrapped

[squigley]

I am aware that NIMH cannot be replaced with Li-ion, it was a temporary replacement based on what I had on hand so I could identify if a failed battery was what was causing the unit to turn off, as I presumed that the adapter alone would not provide enough current and it required a working battery to provide additional current for it to start up and run properly (ie like some phones that if drained too far will boot into a "please wait, battery too low" screen as they require more current to boot up than the charger alone can provide). If the temp battery had allowed the unit to stay on for a few minutes instead of immediately powering off, then I was going to go about ordering the replacement battery or cells.

Perhaps it does, or is supposed to work off the charger alone, I did not try using it without the battery, before I attached too much voltage to the battery connector. It was not dead until I connected too much voltage to the battery terminals, as as I said, it would turn on, but only for a couple of seconds, and then just go off. After I put too much voltage and apparently overloaded the power transistor it now does nothing.

I was looking for advice as to whether it is worth replacing the power transistor or not. I have attached the circuit diagram, showing the voltages I measure. I don't understand how there can be 10v at the emitter of V4000 when there is no voltage at the collector. I am also not sure if the P-ASIC is trying to PWM drive that transistor to drop the voltage, so when I short the collector to the emitter it's passing too much voltage which is what's causing the Garfield ASIC to get so hot.

[squigley]

Oh, I just realised that the symbol on the Fluke schematic is the reverse of the BC869 data sheet, and because it's a PNP, and not an NPN, the voltage is supplied to the emitter, not the collector..

[CDaniel]

I think it is useless to try to troubleshoot this ... you made a big mistake and is gone . 24V >>> 7,2V game over . Only if you can find those ICs .

[noidea]

Just a short comment, these scopemeters will work off the standard power supply even with a dead battery, at least my 196c did when I bought it used with a toasted battery
Sorry I can't help more with any repair suggestions, I'm more of a user.