Got an old Fender Taurus solid state amp to work on here. Got it all fixed up and went to turn it on. From what I have read about all these old Fender solid state amps I expected it to just sound terrible. To my surprise it sounded absolutely fantastic!! It was absolutely silent with nearly no hum at all. It is a great clean sounding amp and I felt a need to post something to let other people out there know that it is not a terrible sounding amp. Of course someone had removed the JBL speakers so I had some old Fender 10" speakers waiting for just this problem. Somebody actually had installed car stereo speakers in the thing!  :trouble Also, the PCB board had leftover flux residue all over that had turned white. Looked like a bird had flown over it and took a dump right inside the amp. Anyway just thought to share this experience about this amp since it is a rare specimen.

Google and youtube can be your best friend in understanding this if you have never done it before.
https://www.youtube.com/watch?v=rrO9FrlSkOM

This gives you an idea how to do this but in your amp it has two wires soldered to the board instead of another plug on the end.

Quote from: Deoxit Huffr on March 18, 2017, 04:46:24 PMAre there any good tuts or walkthroughs around for replacing the RCA plugs?  Do you need to remove everything up to the board? Then I would need to do some soldering, which  I'm a beginner at that too.

Do you have an ohms meter to measure resistance? All you need to do is make sure the continuity from plug tip leads back through the wire to the solder joint on the board, and same measurement with ground portion of each RCA plug. It is possible for the wire to get compromised after all the wiggling around as Phat said. Prove this theory first and then move on to taking voltages on all the pins of the U2 and U4 chip. I think you ruled out a defective reverb tank by plugging in a brand new one.

When you tap on the reverb tank does it make a crashing sound? If so then the recovery side of the reverb is working. Start at least there to see what we are working on. BTW here is the schematic. Might be helpful to test voltages the U2 chip and the U4 chip.

To be honest I don't think it is the output transistors. They are not something that wears down, rather they just break. Things that wear down with age and grow dirt are your jacks, pots, solder joints, and the speakers just to mention a few. I mean transistors can get old and leaky too I guess but lets look another direction.

How do you play the amp (i.e. Style of music)? Do you use the effects loop? How long were you playing the amp and satisfied with the tone?

Have you tried the amp out with a different cab or other speakers? Just a thought that you can try to eliminate the speakers as a possible culprit.

Well if the amp responds by thumping it then it would point towards loose connection or broken solder joints. Before just bypassing the effects you really should try to fix this thing. What is your experience level soldering or working on amps? Take the amp out of the cab and use a chopstick to tap around on the insides. At some point you might trigger a certain area of the board as where the fault is occurring. Looking at the schematic it appears that this is one of those cases where you can mod the amp to bypass the DSP circuit. Still I would fix the problem first since it might be fairly simple.

So...
G100 series 1 reverb = 4AB2C1A
G100 series 2 reverb = >>> 4AB2C1A
G100 series 3 reverb = 4EB3C1B
JX30-50 type amp reverb = 1EB3C1B

As I had followed along I took time to crop all the G100 type reverb circuits to analyze them all. Also, I even started look at the Yamaha JX series amps reverb circuit too. I found a picture of the JX40 type reverb as being 1EB3C1B. At least that is the best I can make out on the picture I found online. Figured I would just post all these in one place so they are here for the looking.

The really old one's have metal type corner pieces on the cabinet.


When operating in chorus mode the depth and speed pots have no effect. In vibrato mode then the depth and speed are used. The first thing I would try in this situation would be cleaning those pots just to rule them out as a possible culprits. Not saying that is what is wrong, but cleaning those pots can't hurt. After that point troubleshooting the circuit will get way more involved.

If your in the USA then I would look at this place for buying the jacks...
https://www.guitar-parts.com/catalog/fender-amp-jack-pc-mount-0

Another one is here...
http://darrenriley.com/store/fender-stereo-amp-jack-0990913000/

From what I gather the original Part# is 0031570000 or 0025931000. As it states on the DarrenRiley site "Fender part# 0990913000  (same as 0031570000 ,  0025931000)"

Quote from: Enzo on December 05, 2016, 04:33:29 AMBut for a small one time set-up fee, I could get them with my brand on them.  So Enzo-cords, or Shiawassee cords, or even Jimi-Jam if I felt like it.

I still think Wangdoodle sounded pretty funny!

Here is a link lightly talking about something that might relate to those speakers.
http://forums.vintageamps.com/viewtopic.php?p=417370

From what I could gather is they are possibly made by RSC, Radio Speakers of Canada. Who knows?? Do you see an RSC stamp anywhere on them?

Also one mention of a Solec amp on DIY site.
http://www.diyaudio.com/forums/solid-state/171776-solec-ic-46-japan.html

That's a nice looking cabinet with that amp! No-name speakers back in the day are probably better than many brand named types of today. Great post keep it up!!

Try disconnecting the speaker and measure the DC voltage reading on the speaker connections. Look to confirm a small 500mv to 1v on the output while metering it on power up. This will tell us if the noise is a DC offset on the output making noise. Sure this can be the amp working normally and as the pro's put it "The amp just wakes up stupidly".

So for that second or two the amps voltages are settling in and it is not perfect so it can make noises. I recently had a Fender amp that put out 750mv to 1v on power up which will then drop to 5mv after 2-3 seconds and it was not normal. However, tracking down the cause of the problem led to a tiny bit of shotgun part replacement, which we don't recommend. In my case I had suspicions that certain transistors were stressed in a failure of other transistors that I had already replaced. I WARN YOU THOUGH... that these types of symptoms will drive even the greatest techs crazy trying to trouble shoot the cause. In the end it may not be a repairable issue and the amp is actually functioning fine. I guess confirming Phatt's question is the best place to start.

I did not see a schematic posted here... I think this might be the one.
https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=8&cad=rja&uact=8&sqi=2&ved=0ahUKEwih_J2mmKXQAhXmllQKHSMhAXgQFggyMAc&url=http%3A%2F%2Felektrotanya.com%2Frandall_rg100_g3_schematic.zip%2Fdownload.html&usg=AFQjCNFLuo2nozgGcq9gCiPLXNb5xJ31TQ&sig2=Pb-mkBb8IPkGwD29fSshLg&bvm=bv.138493631,d.cGw