Epiphone Jr. Mod Question

[DanD]

As a total newbie who wants to progress to building amp kits, I thought that the Epi Jr. platform was perfect to get started on some skills. I bought a new head (V2)and installed the Bitmo Voicing/Gain switch and the tone control/gain mod. I was very pleased when I fired it up and everything worked perfectly. (cool mods!) I ran it through it's paces for about 20 minutes and shut it down. The next day I began installing the Heyboer OT upgrade. First I took close-up digital photos of everything for a reference. (paying close attention to color codes) After installing the new OT, I was ready for some serious fun....but nothing happened. The only sound I heard was a very faint squeal that changed pitch as I turned the tone knob. That continues to be the case even after several rounds of re-soldering AND putting the original OT back in.
I'm hoping for some basic trouble shooting advice. I have a multimeter, but I wouldn't know in what sequence or where in the circuit to check for problems. I would really rather not succumb to handing it off to a tech if at all possible. I'd be grateful for any advice you may have. Thanks.

[loudthud]

The first step would be to check voltages against the schematic. I have no idea what documentation came with your amp. Can you find an online schematic and post a link for us here?

[Chuck_Farlee]

One quick check:

Check to make sure the green wire with the yellow stripe coming off the main PCB is bolted down to the grounding bolt. What you described sounds similar to what happened to me one time when I was modding my VJ. It turned out that I left the ground wire unconnected.

Also make sure the green wire from the output jack PCB is connected to the grounding bolt.

chuck

As a total newbie who wants to progress to building amp kits, I thought that the Epi Jr. platform was perfect to get started on some skills. I bought a new head (V2)and installed the Bitmo Voicing/Gain switch and the tone control/gain mod. I was very pleased when I fired it up and everything worked perfectly. (cool mods!) I ran it through it's paces for about 20 minutes and shut it down. The next day I began installing the Heyboer OT upgrade. First I took close-up digital photos of everything for a reference. (paying close attention to color codes) After installing the new OT, I was ready for some serious fun....but nothing happened. The only sound I heard was a very faint squeal that changed pitch as I turned the tone knob. That continues to be the case even after several rounds of re-soldering AND putting the original OT back in.
I'm hoping for some basic trouble shooting advice. I have a multimeter, but I wouldn't know in what sequence or where in the circuit to check for problems. I would really rather not succumb to handing it off to a tech if at all possible. I'd be grateful for any advice you may have. Thanks.

[DanD]

Epiphone Jr. Mod Question

Thanks everyone for your feedback. Enclosed (if I did it right) is the schematic.
I've gone through and carefully checked all of my mod connections. I can't find any blackened components. All ground wires are secure. Alas, when I power up I'm getting all zeros on my DC resistance readings off the OT leads. Not a good sign heh?

[Ampclutz]

Uh Oh... I hope you didn't really try to take resistance reading while the amp was powered up. If so you may not have a functional meter any more. I hope you really took voltage readings. With no signal going through the amp you may have lucked up and not ruined your meter.

And you did have a speaker or other load connected while powered up?

AC

DanD
Epiphone Jr. Mod Question
Thanks everyone for your feedback. Enclosed (if I did it right) is the schematic.
I've gone through and carefully checked all of my mod connections. I can't find any blackened components. All ground wires are secure. Alas, when I power up I'm getting all zeros on my DC resistance readings off the OT leads. Not a good sign heh?

[DanD]

Epiphone Jr. Mod Question

Thanks Ampclutz. Yep, I assumed that I needed to take DC readings when it was powered up. It appears that I set the meter to read DC voltage. I don't believe that I ruined my meter but I will check it. I always make sure to have a speaker connected and usually a guitar plugged in. I broke down and brought the chassis to a friendly local tech. yesterday. Once repaired, he's going to share his troubleshooting process/sequence and thoroughly go over the schematic with me. I'm going to look into taking some basic electronics classes and do some homework before start breaking stuff!

[DanD]

Epi Valve Jr. Mod Problem Solved!!

I picked up my Epi Valve Jr. head from the local tech today. The following was the invoice service performed description:

Opened amp, traced out dc voltages first; they look ok. Filaments on first tube seem funny; pull board, traces all painted black! Next pulled primary of op xfrmr from board, ran 120 vac into it, speaker still not sounding. Removed jack board, aha! Cracked traces on the board opened black (common) wire to the ground buss. Replaced jack board with handwired jacks. Problem solved.

Thanks for everyone's input!