Something blew on my Pathfinder 15R... help!

[Tarin]

It's been nearly a year since i last posted something here... sorry (i know you did'nt miss me anyway).
Here's what happened with my beloved Vox 15R... rookie mistake: just yesterday i found out that using an instrument cable for a speaker cab ain't a good idea. I read lots of threads on the subject and finally understood WHY... so i went to my local radio shack-type store, bought the necessary parts and did all the soldering and ended up with a new speaker cable for my Vox and my Blackheart cab.
Plugged it in, snack-crackle and... silence__________ (no pop).
This happened immediatly after i strummed my guitar, no chance to turn the amp off before the silence (3-5 seconds).

So, once the cursing stopped, i checked the speaker cable and found out what MY mistake was: one of the 1/4 plugs did'nt have the inner plastic sleeve so the solder joints touched the wall and... you know.

Second step, i checked the speaker with a different amp (and an instrument cable, for now), and the speaker is fine.
Checked my amp's head phone line... no sound.
Line out? no sound either.
Opened the amp for visual signs of... something: nada, it does'nt even smell burnt.
Checked a small fuse on the inside: seems fine.

So, veredict?

 

[Tarin]

Woah! just checked my avatar pic... the only remaining toys are the Gretsch Corvette and the Vox Pathfinder 15R... yep, the same one.

 

[jim p]

some ideas on the problem

Didn’t you start the Crate V5 mod thread a long time ago? I found a schematic here http://music-electronics-forum.com/t9222/ The one linked there is hard to read but searching on the web found threads that stated the output amp IC is a TDA2030. Even though the IC is short circuit protected you may have blown it. You could measure the power supplies in the amp first you should have +/-15 and +/-9 volts. Also could see if you have a preamp output signal if there is one on the amp. If you have the power supplies and a preamp signal that just leaves the power IC they have them at Mouser http://www.mouser.com/Search/Refine.aspx?Keyword=tda2030 You could also consider the TDA2040 also it puts out higher wattage with the same power supply rails so it must be able to get closer to the supply rails at maximum power out. If you replace the power IC you may need to add some fresh thermal compound between it and the heat sink it is attached too. The metal tab on the IC is connected to -15 volts so it needs to be isolated from ground. You need to check if the output IC is a TDA2030 I cannot read it on the schematic I have, but that is what I found posted on a thread on the web.
Solid state amps do not like short circuits they just supply maximum current and go into melt down if no protection is designed in. Even with protection the circuit may not respond fast enough and they fry anyway. A tube amp would have had less of a problem with a short they don’t like opens.
Here are links to the data sheets for the power ICs
http://www.st.com/stonline/books/pdf/docs/1460.pdf
http://www.st.com/stonline/books/pdf/docs/1459.pdf
The only obvious difference between the TDA2030 and the TDA2040 is the power output, but the TDA2040 may be more efficient so it would maybe run cooler and with luck it may have better short circuit protection. It does cost more than twice as much as the TDA2030 though.

There is a TDA2050 also which might be the best choice http://www.mouser.com/Search/Refine.aspx?Keyword=tda20&FS=True

I was just checking your post again and see that you have no line out so it may or may not be the power amp IC. If the power amp IC has shorted out it could be pulling the power supplies down so nothing would work. Because you have no line out the power supplies are probably not up in the amp. Just to be sure on the fuse I would check it with an ohmmeter to see that it is good sometimes they look OK but are open. On the schematic I have there are some 330 ohm resistors in the power supply section one of those could have opened and you would lose a supply rail.

 

[Tarin]

Another thing i noticed... and please, other 15R owners can help out on this one.
When i turn the power switch off, the red light seems to dim out little by little now and i'm almost sure that did'nt happened before the "accident"

15R user: please verify (maybe it's just me going paranoid).

 

[Tarin]

mmmm, made another reply but i guessed it got lost in space... here goaes again:
Thanks Jim P: i'll do all the checking once i have my amp at hand (i'm at work right now), also i'll have to double-check on the "no line out either" cause i'm really not sure i tested it correctly (due to me screaming and waving my arms in the air like a little girl at the time).

BTW: yep, i started the loooooooooong Crate V5 Mod thread.

 

[poodlesrule]

Just checked: Mine takes 1.5 to 2 seconds to dim out to nothing. Yours?

 

[Tarin]

Proven... it's my paranoia.

 

[Tarin]

I just double-checked everything:
No phones out
No line out
No speaker out.

 

[Tarin]

Ok, hands on the project right now.
I just checked the fuse for continuity... it does have, so no problem there.

 

[Tarin]

OK... i whas in the middle of pulling tha chasis out when i noticed the IC is actually broken in half. Thanks Jim P for addressing this as a possibility.
Is it normal for IC's to break in half? i wonder.

 

[bcdon]

OK... i whas in the middle of pulling tha chasis out when i noticed the IC is actually broken in half. Thanks Jim P for addressing this as a possibility.
Is it normal for IC's to break in half? i wonder.

ICs can break in half, shatter, burn, you name it. Given a little too much current the casing can just explode. If the IC just broke like this you might be in luck, make sure the traces on the PCB are okay and drop in another IC.

 

[Tarin]

Yeah, all tracings are still good, i got the broken IC out with no problems. Now for thestupid question: are IC's easy to find? i mean, does a regular electronic store carry them? Thing is i live in Mexico, right on the border to California so, i could do a google-search of any electronics store in San Diego and just drive there OR, i can just order it and wait for Mr. Postman... i'm almost sure i won't find it in Tijuana.

 

[bcdon]

Try: www.mouser.com http://components.arrow.com/products/ http://www.digikey.com/ or some other online retailer.

 

[jim p]

As I posted above you may want to use a TDA2050 instead of the stock TDA2030 it costs a bit more but it may be a better part. Also the metal tab on the IC should have been connected to a heat sink and the tab may need to be electrically isolated from the heat sink if the heat sink is connected to ground. The tab on the IC is connected to the negative power supply rail. Check the original parts installation look for a shoulder washer on the hole on the tab and an insulator between the tab and the heat sink. Also you may want to get some fresh thermal compound for between the IC tab and the heat sink. I would consider getting two replacement ICs just to play it safe if something goes wrong on the first replacement also with the shipping cost it will even out the cost a bit. Digi Key also stocks the parts as well as Mouser Electronics.

 

[Tarin]

I was wrong about my country carrying those IC's! Went to my local mom-pop electronic store just in case, wadd'ya know, they had them in stock, lots of'em 2030's 2040's and others... i went with the original TAD2030, i've always liked my 15R for what it is.
They also had small amp building kits with all the necessary parts for you to make a 15W or 18W amp (sooner or later i know i'm gonna buy one... see what comes out of it).

The replacement was a piece of cake: there was enough heat compose to spare, there's an isolation plastic between the chip and the heat sink, also between the little bolt and nut... solder 5 points, build everything up... IT'S ALIVEEEEEE! i screamed (i really felt as if had built the whole amp from scratch).

So there we have it, end of the story... but not of my 15R, it's been 3 years now since i bought it, swapped the 8" for a 10" speaker... got a Blackheart 1X12" and now i converted my 15R to a head unit (now i have an original 8" and a Jensen MOD 10-35 laying around... Ebay comes to mind). And now this little surgery. I know i'll keep this little amp untill it really gives up on me.

Once again, thank you all for being the gtreat bunch you've always been... if you're someday in TJ, taco's are on me!

 

[bcdon]

Great news!

BTW, I love me some tacos! ;-) :dude

 

[jim p]

Good to hear you got it fixed. Probably a plus you found the part at a local store with the added cost of shipping if you had to order it from Mouser or Digi-Key.

 

[Tarin]

Yep, cost me 30 pesos (about 2.50 dollars).

 

[jim p]

If you look at the Amps & cabs section there is another Pathfinder problem where the optocoupler goes bad http://www.thefret.net/showthread.php/15546-Vox-Pathfinder-15-Doesn-t-seem-quite-right. Something to keep in mind if you have a problem like that in the future. I think Mouser was $1.65 for the TDA2030 but shipping would probably been more than 10 bucks so a good deal on finding it local.

 

[Tarin]

Well, after almost a week of almost no use... my IC blew up again? no suspicous cable this time.
What could be wrong?
Since i succesfully placed a new IC a few days ago, the amp was used for about 5 hours at the most on the following days, then, me and the wife went to Vegas for the weekend (please excuse me... a tear just rolled off my cheak) and when i returned, i plugged my well known 15R and for about 10 to 20 seconds i started hearing the same'ol snap-crackle-______________ silence.

Could humidity be the problem?
I took the amp to my office where i had a bit to much water leaks from the rain that hit us a few days back... the place is very humid. Other than that, all connections, wires and such are OK.

Help... again!

(I'm fixing a hole, where the rain gets in... Beatle Love show made the Vegas trip worthwhile)

 

[jim p]

There some types of solder flux that are hydroscopic (water absorbing) and can become conductive, but they usually won’t conduct much current. I would look at everything carefully before you take the TDA2030 off the board and check for shorts at the speaker jack. On the schematic there is a 1 ohm resistor with a capacitor in series to ground I would check that capacitor to see that it is not shorted. Make sure the tab on the TDA2030 did not get shorted to ground maybe there could be a bad insulator or cracked shoulder washer. Hope you find something obvious as soon as you give it a good once over.

 

[Tarin]

Update on my 15R

Thanks for the advice JimP... i did'nt have a chance to open the amph up untill today BUT, before i started the surgery, i plugged everything back up and gave it a try... ya'know, just in case.
As soon as it powered on it began to HUM... turned it off!
Checked everything physically (from the outside, of course) and guitar cable, speaker cable, gain and volume knobs... everything was OK so i turned it up again just to hear that HUM again SOOOOOOOOOOOOO... i abandoned my duties and logged into Thefret.net

Now what?

 

[Ch0jin]

Sorry to hear that, but, speaking as a tech, I'm not super surprised. I'm not familiar with the circuit for this amp, but years of fixing broken stuff taught me that catastrophic failures (chips broken in half) will very often damage other components. The other thing to keep in mind is now that it's failed the same way twice, the cable might not have been the root cause. As Jim said, I'd check the schematic and inspect/replace and DC filtering caps both in the power supply section (excess ripple could cause the chip to explode over time) and the power amp section. Given that you played it for 5 hours before it blew again, that sounds like capacitor to me rather than semiconductors. If I had it in a workshop I'd check grounds, replace caps, then the IC, then check all the voltages for the power amp section, then check them with a scope for excess ripple.

Then again I'm just saying what I'd do not knowing the amp. A tech who works on these amps all the time might know exactly what this is right away. After all, faults with electronics tend to be fairly common in the same model.

 

[Tarin]

Back from the dead again (for now)...

Wow... that seems to be too much work... for me.
Before a read the last post, i went ahead and opened the amph again searching for obvious signs of... something. And what i noticed is that it might have been my fault: excess solder in one of te IC's pins.

I noticed a big drop of solder ran down the pin... i don't know if IC's get to be that hot that the excess solder i applied melted and ran down the pin untill it dried up and managed to touch another pin. Or maybe this happened as i was soldering and never noticed the excess running down... thing is, i saw a big dried up drop that seemed to be touching another pin.

BUT, now that i've read this last post i'm finding out it could be lots of thing... i guess time will tell (a lot of time i hope).

Anyway... thanks for every advice, i know you guys are always willing to help.

 

[Ch0jin]

IC's do NOT get hot enough to melt solder under typical operating conditions so you can rule that out. It is possible it happened when you first soldered it in, but it's pretty unlikely the amp would have run for 5 hours with a dead short somewhere. Unless the short was almost complete for hours, then a bump or vibration complete the short. You mention it's running again now so the IC you replaced is still physically OK? No cracks or anything? Did you clean up the soldering?

As luck would have it, I was playing through my Ultra this afternoon and as I pressed the boost button I got no signal and massive loud hum. Slap the amp and it goes away. I've yet to pull it apart, but I'm 90% expecting to find dry solder joints on filter caps to be the issue. It's been running flawlessly since '96 so it's probably about time I pulled that chassis out for a perv anyway.