Learning to repair my gear...Squier 15G Solid State Help

[52 Bill]

For what it's worth...

Some of these amps have the filter caps glued down to the board with what looks like brown contact cement. There is very little liquid in any modern electrolytic capacitor. At least not enough to leak out and drain onto the pc board.

Is the amp humming or buzzing really loud? Does the hum diminish as you turn down the volume control?

From your description of the symptoms, I'd first check the input jack and then the controls. Check to see if the jack has pulled up out of the board, either breaking the solder connections or breaking the traces on the board itself.

If the jack is ok, then check the pots for broken elements. If the pot has been flexed too far or smashed from the front, the resistance element will sometimes crack breaking the signal path. If this has happened, the pot will read open with an ohmmeter and the top section will pull or flop away from the terminals that are soldered to the pc board.

If the pots are all ok, then look for either broken or loose signal caps or a bad first stage IC.

Hope this helps.

[Lee W]

Thanks 52 Bill.

I checked the input jack (as that was my first suspect) by plugging in a cable, and checking the tip/side of the cable to where the jack is soldered to the PCB, measuring 0 ohms. This indicates the jack is good, as far as I can tell. I also tested resistance between the jack and the next components on the PCB, got 0 ohm readings as well, indicating there are no breaks in this part.

I do get a different volume of hum when I change the volume and gain settings, but the same amount of background hum as I recall is normal from this amp when it was working, but this was several years ago. From the symptoms I immediately thought it was either the input jack or a preamp problem, so a faulty preamp chip seems to be the most likely culprit from my limited knowledge, and what everyone is seeming to recommend checking.

I'll first go through all of the pots to make sure they are functioning properly, and none of the traces are broken around them.

This board is so helpful, I can't believe the amount of detailed responses I've received for such a minor amp!

Edit: Ok I checked all of the pots, they all work great in both directions (check between lug 1/2 when counterclockwise, then check between lug 2/3 when clockwise to get a 0 ohm reading. My meter was on 2k setting and got infinity the other way...except for cases where the lugs were on the same trace, then 0ohm obviously ). I also checked all the traces around each of the pots and all was well on the ohmeter. It's got to be the preamp chip at this point....I hope haha

[Lee W]

Hey guys, back after quite a while. Took a little time for the parts to come in...but...IT WORKS!

So I did what you guys said and replaced the preamp chips. There were two TL072CP in there, and I replaced them both. Used solder wick to remove them which worked great, and installed a socket into the PCB which was quite easy. Now if they get wrecked again I can just snap in new ones.

So I was nervous plugging it in the first time, but all was well. And I only electrocuted myself once...

I had it all apart when I turned it on the first time, and touched the back of the on/off switch which was wired into the power cord. Well I know better now haha.

All in all I had to say it was a great experience and I have to thank you guys a lot for taking it back to basics and helping me out. I understand now what was meant by this is very different from a tube amp in troubleshooting. Instead of finding out why preamp tubes aren't getting the right power etc., I just had to replace some IC's. But during the process I learned a lot about troubleshooting, soldering, and safety. I also built myself some little clip and resistor tools for draining filter caps. I guess I thought I was safe from getting zapped because I was so careful with the filter caps that I just touched the switch without thinking

Now my next task will be retensioning the tube sockets in my JCM900 and biasing it. Just got my bias probes in and found out it's running wayyyyyyyyyyy cold. I can't wait to hear what a difference this is going to make!

[SteveG_in_MD]

Thanks

Is this the critter?

I found this Squier 15 Amp schematic about 12 years after the original post. It is what I'm looking for. I'm replacing all the pots in mine because they sound scratchy. One even drops out in some places. The replacement pots are only about 75 cents each at Digi-Key. I only lifted one of the single-sided pads during de-soldering. I hate single sided PC-boards, which all inexpensive amps seem to have. Anyway, thanks for posting this schematic. Since these amps are not considered by Fender to be repairable, they don't have the schematic available for techs. I'll check this schematic against the circuit board to see if it's the one.

[Enzo]

Welcome

I was an authorized Fender repair shop for decades, and I have a Squier Champ 15 schematic.

Fender always provided schematics for amps on the do not repair list. Do not repair means they won't pay for warranty repairs, they prefer to just replace. it does NOT mean the amp is unrepairable.

[Jon Snell]

Be very careful when setting the quiescent current, there are lethal voltages in there, very close to where you place the probe!

[Enzo]

Well, the Squiers are chip amps, so there is no adjustment to make. But certainly respect the mains wiring.