Nevermind.....SOLVED!

[JKD]

Well..I have one MOD50 that was a GC special (really low price) that I only bought as a backup and pretty much got what I expected....the 'Low Pwr' option doesn't work right but right now my MAIN MOD50 AMP **** the bed today :-(

The output is just 'low', i.e. have to crank up the Master to get shitty output (I didn't crank it far) - so far:

1. Used know working guitar cable from another amp
2. Changed to known working speaker cable from another amp
3. Different cab and/or OHM combination
4. Cleaned or jumped FX loops
5. I replaced all pre-amp tubes just in case
6. Known working power tubes from another amp and re-bias
7. Different modules
8. Plugged straight into FX loop (yes I do get sound)


Pretty much stumped now...have to think something failed inside. anyth else to try?

9. Possible that a POT failed but none of 'em sound shitty and all feel smooth still
10. Cold solder join somewhere?????

 

[Jaded Faith]

The MOD50 I just modded and shipped back home today had the same issue. There's a couple things it could be, so you really need to be proficient at troubleshooting to find the failure point. I would pump a signal generator through the front end and watch the signal on a scope to find where it drops off. I did the repairs for $60 on the one here in addition to the $450 in mods I did to it. Email me if you need help.

 

[JKD]

Honestly Rob, I'm tempted to send it to you for Mod work (love the NFB concept) and fixing but right now I don't even have money for shipping...LOL

I'm going to pull the chassis and check a couple things I can on my own but my knowledge is very basic so I'll email in the new year and Thanks for your kind offer

 

[JKD]

FYI - it seems like #8 was the clue, since I can run a pre-amp into the FX Return and get full sound. This confirms power section is working fine.

I have traced it to some issue on switching with pre=amp section in head.

Does the MOD50 use the same opto isolators/switches as the Randall?