Capsplosion in a two-way CB radio - Need help identifying melted parts (photo warning)

[MarkNutt]

I just made the mistake of buying a CB radio for my 4wd sight unseen with the innocuous warning "doesn't turn on, might have been connect back to front".

A simple case of a blown fuse or diode I thought! Ha!

Anyhow, can anyone here help me to identify some of the melted parts? Even an idea of what they might be based on what's around them would be a huge help.

Here are some photos:

Parts 1, 2 and 3 - I'm mostly interested in part one here as it's obviously got to be replaced and I don't have the foggiest clue (maybe a regulator). It is screwed (using the one next to it) to the metal of the heatsink at the top of the photo so I'm guessing on a linear voltage regulator of some sort.

As for part two - is that little bubble in the centre normal? It otherwise looks okay.

Part three - haha some misc. little SOT23. Good luck chaps! I'm guessing the strangely bubbled up plastic isn't normal? Hopefully I'm wrong and sometimes they're just made like that.

Now for the offending capacitor - I'm guessing either a result of that "regulator" failing and/or being connected in reverse polarity. The vent never broke, the whole body just popped up. They are all "ISHK" brand (I think). Heard of them? No, I didn't think so...

Thank you very much in advance! I guess you can imagine how disappointed I am (it wasn't that cheap for it's condition)!

 

[davenn]

hi Mark
welcome

since you haven't told us what make and model the radio is, and the mess inside, its pretty impossible to tell

have you a circuit diagram, most transceiver gear has a diagram in its manual
failing that, have you gone to the manufacturer to see if you can get any service info ?
or have you googled the make and model to see if there is any info online ?

have a go at those things and report back

cheers
Dave

 

[MarkNutt]

Hi Dave,
Thanks for the welcome! Sorry, it did cross my mind but I'd originally decided not to. Not sure why now, so here you go.

It is an "Oricom" brand, which is a local brand that isn't cheap rubbish but not high-end either (the "does the job and does it well for the price" type).
The model is "Oricom uhf180". It has Australian & New Zealand regulatory marks N13134 Z765.

Sadly no, I could find any circuit diagrams for it and given it's market I do not believe they would publicly release them either. That's why I suggested even if people could advise what they feel the components could be given their locations I'd appreciate it. For part one, I haven't come across that package before and haven't had any luck finding it online, let alone that specific part. It appear to be a quad four pin chip with a pin in the very centre of each side.
Thanks!

By the way, here is an overall view of the circuit board. It is a two-sided board and doesn't appear to be multi-layered.
Here is the upper side (now a bit cleaner but still a fair bit of capacitor fluff): This is full resolution, the link is http://i62.tinypic.com/5mio3k.jpg

Here is the bottom side (no visible damage aside from what looks like messy flux):

 

[MarkNutt]

The "uh-oh" is a lifted trace for the main 12v positive in, in case you can't see it clearly, by the way. Not a big deal to fix, but that there was enough current to do it is what worries me!

Edit: for what it's worth - here is the user manual: www.cbradio.nl/oricom/Manual_Oricom_UHF180_ENG.pdf

It mentions that it is a 12v radio and will not work on 24v (truck) systems, however it can safely be connected to up to 30v but will flash a warning and not operate until voltage is dropped to a max of 15v. So that rules out the person trying to fit it to a 24v source.

It has the following protection:
Over-voltage: diode and voltage regulator
Over-current: 2 Amp fuse
Reverse polarity protection: shunt diode


To be honest, I don't have a clue what that little four pin quad pack is. It's not near the power circuit so it's not what I thought yet it needs the heatsink connection underneath it?

 

[davenn]

OK thanks for that,

that 4 pin device you circled as part one in the first pic is the final output transistor ... part two is the driver

I would day there's a pretty high chance that the damage done to all was because of the power being reversed
the capacitor, circuit track are a high indication of this. The final transistor will have its DC supply direct from the 12(13.8)V input
hence its demise

could it be fixed ... with circuit info .... YES, without info on part types, very difficult to impossible
the other thing is also, we don't know how much other damage has also been done from the reverse voltage
other parts may have failed but not visibly

Dave

 

[davenn]

There's user manual links to the unit on the www .... there's a new Zealand www site and phone numbers you should check out
they may give or supply at small cost the schematic
if you don't ask, you will never know

Dave

 

[MarkNutt]

the other thing is also, we don't know how much other damage has also been done from the reverse voltage
other parts may have failed but not visibly

This is what I'm fearing the most. It didn't cost me an arm and a leg but it wasn't that cheap and for the money I could've gotten something working but with a few less features...

I did find the user manual (I edited my last post with some bits from it) and I do have the company's details here in Sydney, Australia (www.oricom.com.au) but not being a higher end manufacturer I highly doubt I'd see any diagrams.

You are right, though. You never know unless you ask. I just am not sure how best to ask to minimise their work so I might actually get something. I've found in the past with "budget" electronics companies that they never give out any technical information let alone diagrams or part lists. I was half hoping someone here might even have one of these that might be willing to pop open for a photo!

I can't say I've ever seen that package for a transistor before. Interesting.

 

[MarkNutt]

Never mind They replied with the PCB layouts and circuit diagrams eight minutes after I emailed them...

The transistor is 2sk3476 and I'm yet to look up the other bits but now I've got to track them down. What do you think is the best source for one-off components? Believe it or not, but the 2sk3476 is on eBay hahaha (for $6.81 from Hong Kong...) Can you suggest a better place?

EDIT: Also, what do you think is the likelihood of other components being dead?

 

[MarkNutt]

Part one is 2sk3476
Part two is 2SK3078
Part three is KDV804S

 

[MarkNutt]

Oh, never mind about part two and three. The "melted" case just had some stray flux on them. It scratched right off...

I feel like a bit of a git now...

So, to recap:
-Repair trace
-Replace cap
-Replace output transistor
-Replace shunt diode (I assume)

What might be the likelihood that that's the extent of the damage do you think?

 

[davenn]

a good chance that's all

its worth a try and see if it works .... the cap you probably could use something like a 1000uF 25V
the shunt diode ... if its faulty ... yup replace ... you could use something like a 1N5404

looks like you will have some circuit track repair/cleanup around the output transistor once its removed

initially leaving the output transistor out of circuit, and not pushing the TX button, you could at least see if it receives any local signals

 

[MarkNutt]

Thanks, I was actually just about to ask if I could remove the output transistor to test the RX circuit. That would give me some peace of mind if I can.

 

[davenn]

the eBay choice for the output transistor is probably as good as any

see how you go and let me know, if the receive is stable, that will be a great start


just for your info.... Im an amateur radio op. been licenced since 1980 initially in Dunedin, NZ
then got an Australian callsign when I moved over here in 2000
been building radio gear for many years. Am not just a "black box" operator as many hams are

 

[MarkNutt]

Ah, good to know! I've considered getting my licence (I do own two cheap dual band radios, but never TX of course ) but to be honest I'd rarely talk so I can't justify the cost. I just like to browse around and listen!

Once I get the time I'd like to build my own radio, at least for the 477MHz CB range (so it would be erm 'legal'...-ish... and only 5w honest!), sadly I barely have the time to fix this CB...

That said, I will get to it on the weekend or so and I'll let you know how I go!

 

[Electrolab]

It is always nice, to find a cooperative company, you can deal with. Now I am looking forward to hearing the end of this story!

 

[davenn]

Once I get the time I'd like to build my own radio, at least for the 477MHz CB range (so it would be erm 'legal'...-ish... and only 5w honest!),

It would be totally illegal ... CB gear either 27 or 477 MHz has to be commercial and type approved
so any construction at all is illegal
that's the fun part of being an amateur operator, you are allowed to build your own gear, antennas etc
because it is the amateur operator that is licenced NOT the gear.
For CB radio and other commercial radio gear in taxis, delivery trucks etc etc , its the gear that is licenced NOT the operator
It was the major reason for me to move from CB to amateur over 30 yrs ago


cheers
Dave

 

[MarkNutt]

I have had success with repairing the radio to a point where the RX appears to be working perfectly and I am now waiting on a replacement output transistor from Hong Kong to repair the TX side.

The repairs simply consisted of repairing the lifted and split trace, replacing the two input caps, replacing the shunt diode and replacing the link cable from the radio to the head display (had some breaks and I needed to use up that old CAT5 and now it's much longer ).

Now for the bad news. Despite using very low heat and air volume the pads popped straight off the board with the old transistor. I get the impression that no matter how careful I was, that was going to happen regardless. Hopefully it won't be a problem, but there isn't a huge area to solder it to. The bare board is present under it and it is also a multi-layer board after all as well. Seeing as it is the output transistor I obviously don't want a bad joint on it either so that will be fun when it comes to it. I'll upload a photo later if anyone is interested.

For now I have it reassembled and connected in the 4wd for receiving only. It can also receive from 400-520 MHz (no digital decoding obviously) in additional to the usual 477ish MHz CB frequencies, which is nice.

 

[MarkNutt]

It would be totally illegal ... CB gear either 27 or 477 MHz has to be commercial and type approved
so any construction at all is illegal
that's the fun part of being an amateur operator, you are allowed to build your own gear, antennas etc

Ah, shush. In my heart I know there's not really any grey zone. I just really cannot justify the costs involved to get the licence, sadly.

Surely antennas at least don't have to be commercial? I was going to build my own for a home base station, I guess that's off the charts now... =(

 

[davenn]

LOL sorry to burst your bubble

and for the stinger .... even you doing the repair work on that radio you have automatically voided its type approval unless you are a registered RF electronics service business


but I aint gonna tell anyone

Antennas ... well it used to apply to antennas as well ... I haven't seen a recent set of rules
info would be available from the ACMA


Dave