# Imported Battery Roasted My Rohde & Schwarz FHS6 Spectrum Analyzer

#### Sir Kit

Joined Feb 29, 2012
44
I ordered a generic drop-in replacement battery from China. Plugged it in (keyed socket) and noticed a gunpowder-like burning smell. Unplugged it, reinserted old battery and connected AC adapter hoping for the best. Previously working instrument is now dead. Value $3000-4000. Generally speaking, is it worth attempting a fix? I presume the damage is due to reverse polarity from a mis-wired battery. Is it likely to be widespread (like into IC's) or confined to a few replaceable components I can trace back from the battery socket? Does this sound like a common event? Should I have known better? Bad day. #### ericgibbs Joined Jan 29, 2010 9,574 hi SK, Did you observe and follow the CAUTION instructions printed on the battery label, before attaching the battery.? E #### Janis59 Joined Aug 21, 2017 1,061 Oh sorry, I may immagine Your feelings. Probably Wuhan virus criscrossed the wires?? Know, ill worker shivers the eysight thus the before-to-at last-fall those soldering he do in wrong colour in hands.... RE: Gibbs - dont believe the 7V2 may be misread as 72V. But polarity that is very high probability factor. Thread Starter #### Sir Kit Joined Feb 29, 2012 44 hi SK, Did you observe and follow the CAUTION instructions printed on the battery label, before attaching the battery.? E It's just a battery. And yes it won't work unless "charged before use". That should happen automatically once installed. #### ericgibbs Joined Jan 29, 2010 9,574 hi janis, I mean this caution. E #### ericgibbs Joined Jan 29, 2010 9,574 It's just a battery. And yes it won't work unless "charged before use". That should happen automatically once installed. hi SK. It could be read as must be charged before being connected.?? ie:use E Update: Connecting the uncharged battery to the analyser, may have overloaded and damaged the units internal charger circuit. Last edited: #### Hymie Joined Mar 30, 2018 762 Before consigning such a valuable piece of equipment to the bin, I’d open it up and inspect for visual damage, I’d even consider connecting a known good battery pack. If it is completely dead, check fuses and PSU output voltages etc. Personally I think you have been very unlucky, in my experience the downside of cheap generic battery packs is not meeting the claimed capacity and/or limited life (not reverse polarity). Thread Starter #### Sir Kit Joined Feb 29, 2012 44 Update: Connecting the uncharged battery to the analyser, may have overloaded and damaged the units internal charger circuit. If an uncharged battery can cause overheating, as described in my OP, I would like to know how. No other power source was connected. Unlucky, yes. I will check the board for burn marks. Here's what the meter looks like inside if anyone is interested. #### dl324 Joined Mar 30, 2015 10,072 Value$3000-4000.

Generally speaking, is it worth attempting a fix?
Definitely worth an attempt. If you can't repair, it's worth having a professional give you a quote.

Look for damaged components around the battery. If you want help from us, trace the circuitry around the battery and post the schematic and well focused pictures of anything suspicious.

#### Sir Kit

Joined Feb 29, 2012
44
Thanks for the responses so far.

I removed the main board. Please refer to attached photo. What looks like a 15R Dale resistor was the only part visibly burnt. I am not that familiar with SMT. Looking at the relative size, can anyone estimate the current rating?

I am hoping that is the extent of the damage. But was wondering if I should also replace any of the three other parts indicated below. I tried searching the etched-on numbers with no success. Can someone please tell me what they are (as in equivalent parts), and, knowing this, the chance they might have been damaged as well?

The red rectangle indicates the battery input. There is a wide track leading from the third pin through the resistor to the lower two parts. Judging by the mated black wire on the battery connector, it is supposed to be ground. The far right pin or fourth is red.

I still do not understand how the new battery would cause this damage, but I would like to know. Looks like a case of reversed polarity.

#### dl324

Joined Mar 30, 2015
10,072
I am not that familiar with SMT. Looking at the relative size, can anyone estimate the current rating?
Power rating depends on size; just like through hole (except that TH has a few complications now):

#### dl324

Joined Mar 30, 2015
10,072
How can this occur in a top end instrument?
It happens. At least you found the cause and a fix. Maybe you could convince them to do the repair for free.

#### atferrari

Joined Jan 6, 2004
3,793
After replacing the original with a generic battery? They have the perfect reason to excuse themselves, I guess.

#### Sir Kit

Joined Feb 29, 2012
44
Well I am still curious about why this happened. The page linked above references a special service document explaining how to not short the battery when installing. Why would this be a concern given the keyed nylon fitting?

In addition, the full service manual advises to have the AC adapter plugged in. Again, what is the reasoning here?

I have changed a lot of batteries and this is new to me.

#### atferrari

Joined Jan 6, 2004
3,793
Well I am still curious about why this happened. The page linked above references a special service document explaining how to not short the battery when installing. Why would this be a concern given the keyed nylon fitting?

In addition, the full service manual advises to have the AC adapter plugged in. Again, what is the reasoning here?

I have changed a lot of batteries and this is new to me.
Cannot imagine how many of these got damaged in their own technical service...!

Nice nickname, BTW.

#### KeepItSimpleStupid

Joined Mar 4, 2014
3,910
A lot of things are on all of the time so maybe the AC adapter takes the load off the battery. Li-ION doesn;t like charge and discharge spikes. I have a 212 Tek scope and it won;t really work without a battery pack and damage can occur if used without one.

#### Alec_t

Joined Sep 17, 2013
10,918
In addition, the full service manual advises to have the AC adapter plugged in. Again, what is the reasoning here?
Perhaps there's some volatile memory which stores calibration or settings data and needs a constant supply voltage?