A friend brought over a dead Frontman practice amp. After a little reading, it seems the most common problem is a blown TDA2050.
Even though I rarely work with IC's (and know little of this type of stuff), I did actually have a bunch of TDA2040's laying around. After some more reading, it seems I can sub one for the other, but what differences should I expect? Do I have to alter R40 or anything else?
http://www.e-dan.co.uk/electronics/TDA2040.html
http://blueguitar.org/new/schem/fender/frontman15g.gif
thanx
I believe the only difference is the power/voltage/current rating. If it falls within the scope of the amps power supply/speakers go ahead.
TDA2050 is rated for 32W output while TDA2040 is rated only for 20W output, so most likely the 2050 can dissipate more waste power than the 2040.
I would not recommend TDA2040 for replacement of TDA2050. Assuming pinouts are compatible such swaps generally are "safe" when you replace a lower power chip with a higher power one, but not the other way around.
You can learn a lot by reading.
TDA2040 absolute maximum supply voltages: +/-20V.
Frontman 15 supply voltages: +/-23V nominal, un-regulated (will be higher in that bad-wired club with 130V coming out of the walls).
If a 20V chip fails at 23V, you can NOT complain to the maker. That's why they put ink on paper: to define what they will and will-not stand behind.
Yeah, I know: these chips are a glut on your bench and you won't be complaining to the maker. But if it fails, you sure will be complaining to yourself about extra work and wasted time.
I give 99% odds it will work, on the bench, for an hour.
I'll even bet a buck it works for months. (I've done worse things and didn't get bit for years).
I would not send a friend out into the world with a 20V chip in a 23V amp. It's gonna fail. (Especially if he already killed a 2050.) Murphy's Law says it will fail at a bad time (big audition, etc).
Thanx much for all the replies. It's just a cheap practice amp so not many worries about where it fails.
I did throw in the 2040 and the fuse blew instantly as it did with the 2050 I removed.
According to many, that amp has an issue when headphones or something else is plugged in. In this case it was a talk box.
http://music-electronics-forum.com/t10336/#post112072
http://forums.fender.com/viewtopic.php?t=24618
A few others mentioned that it also could be the J111 fet, but I actually pulled and tested that before replacing the 2050.
I'm going to order a few 2050's and try again. If the fuse blows again, I'm not sure where to go next, since the solution to this problem seems to be a blown 2050 90% of the time.
Quote from: LucifersTrip on August 04, 2013, 03:52:44 AM
Thanx much for all the replies. It's just a cheap practice amp so not many worries about where it fails.
I did throw in the 2040 and the fuse blew instantly as it did with the 2050 I removed.
According to many, that amp has an issue when headphones or something else is plugged in. In this case it was a talk box.
http://music-electronics-forum.com/t10336/#post112072
http://forums.fender.com/viewtopic.php?t=24618
A few others mentioned that it also could be the J111 fet, but I actually pulled and tested that before replacing the 2050.
I'm going to order a few 2050's and try again. If the fuse blows again, I'm not sure where to go next, since the solution to this problem seems to be a blown 2050 90% of the time.
If its blowing fuses, wire yourselft up a lamp current limiter ( http://www.geofex.com/article_folders/spo_test.htm ), so you can take measurements to diagnose where your problem is without blowing the fuse. And take caution working on live AC equipment obviously.
The JFET can't possibly be blowing a fuse.
> the fuse blew instantly
Take the chip out, then power-up. Does fuse blow?
If so, suspect/replace the main power rectifier and the two big electrolytic caps.
Yes, lamp-limiter is wise. Use 45W-60W *incandescent* lamp.