broken amps

[johhno]

Hi this is my first post here but probably not my last as I sit here surrounded by dead or broken amps some my fault and some perhaps not! however I have just got a roland jazz chorus 120 which works fine but all effects do not work so no chorus,reverb or vibrato and I know nothing about electronics.I there an easy fix for a non expert to carry out?

[nickb]

Hi this is my first post here but probably not my last as I sit here surrounded by dead or broken amps some my fault and some perhaps not! however I have just got a roland jazz chorus 120 which works fine but all effects do not work so no chorus,reverb or vibrato and I know nothing about electronics.I there an easy fix for a non expert to carry out?

I wish I knew the answer to that! I'm having a hard time in coming up with a single fault that would kill all the effects. Maybe others might have a good idea. Can a non-expert do it - yes! The key to success lies in common sense tempered with caution, soldering skills and the ability to follow directions, IMHO.

Here's a schematic as a starting point Roland_jazz_chorus.pdf

[johhno]

I wish I knew the answer to that! I'm having a hard time in coming up with a single fault that would kill all the effects. Maybe others might have a good idea. Can a non-expert do it - yes! The key to success lies in common sense tempered with caution, soldering skills and the ability to follow directions, IMHO.

Here's a schematic as a starting point Roland_jazz_chorus.pdf

Thanks for the schematic.It looks like a lot of lines and hieroglyphics to me at present but I will try to fathom it all out!

[J M Fahey]

and I know nothing about electronics.I there an easy fix for a non expert to carry out?

Sorry but no.
Lately I am seeing a lot of similar requests, both here and at SSGuitar, where there really there is no useful answer.

No problem at all helping a Tech or Tech minded Musician with some experience who is stuck with some problem, but who knows how to measure, identify bad parts, etc. , but Electronics 101 is way beyond what can be explained in 1 post ... or 40 .

The proper answer here is:
1) get a schematic
2) measure that all PSU voltages are present and reach where they are needed
3) measure DC voltage at transistor/tube plate/collector cathode/emitter/base to detect any abnormal ones which may point to defects
4) or if Op Amps, check that on output pins there is 0V DC
5) inject 100mV 1KHz at the input and trace it along the path to check whether it distorts or disappears.
Scope preferred, audio tracer acceptable, audio millivoltmeter third option.

Only *after* such tests are made and evaluated, we can really start offering suggestions based on "something"; anything else is just guessing.

[Justin Thomas]

What Juan said!!!

Maybe the first few times, you could politely ask to watch or for a few lessons from a tech in exchange for a few shop chores... Also, there is a safety issue - electrocution is something you only get to experience once. Don't let nickb's signature happento you!

Justin