Stage Line 500W amp repair, help please

Thread Starter

Rookieme

Joined Jan 26, 2021
44
Hi all, new to this forum, i am currently trying to repair an old 500w stageline amplifier, i am relatively new to electronics and circuitry and any help and guidance would be realy appreciated, i do have a schematic for this and have already replaced a number of parts, mainly transisters, some diodes and have all new output drivers,

Cheers

Pete
 

Thread Starter

Rookieme

Joined Jan 26, 2021
44

LesJones

Joined Jan 8, 2017
3,176
You have still not given any indication of the fault So it looks like it is going to a long thread if we have to try to guess what the fault or faults are. So my first question does one chnnel work as expected but there is some kind of fault on the other channel ?

Les.
 

Thread Starter

Rookieme

Joined Jan 26, 2021
44
You have still not given any indication of the fault So it looks like it is going to a long thread if we have to try to guess what the fault or faults are. So my first question does one chnnel work as expected but there is some kind of fault on the other channel ?

Les.
Hi Les,

I currently have the outputs on the right chanel removed, i will refit them tomorrow and list the current faults, neither chanel is working at the minute,
Pete
 

LesJones

Joined Jan 8, 2017
3,176
Are the +45 and -45 volt rails at about the correct voltage with respect to ground ? What is the DC voltage level on the output with respect to ground ?
Re post #9 I think it is best to get the DC conditions correct before tracing signals. The signal generator and scope could be useful to trace faults that cause distorsion.
Les.
 
Last edited:

Thread Starter

Rookieme

Joined Jan 26, 2021
44
Are the +45 and -45 volt rails at about the correct voltage with respect to ground ? What is the DC voltage level on the output with respect to ground ?

Les.
Schematic shows +45 --45 and also a + and - 55v input , 45v reads around 63v and 55v around 72, taken relative to the 0v rail but there is no load on it at the moment
 

Thread Starter

Rookieme

Joined Jan 26, 2021
44
Schematic shows +45 --45 and also a + and - 55v input , 45v reads around 63v and 55v around 72, taken relative to the 0v rail but there is no load on it at the moment
When you say output you mean the actual output of the amp that connects to the speaker port ?
 

Thread Starter

Rookieme

Joined Jan 26, 2021
44
I would not order anything until we have made an assessment of the situation.
The basic tools you need for now are a DMM and a soldering iron.

If you have a music source and a PC amplified speaker those may come in useful.
Have a source, no amplified pc speaker, sure i could find one though
 

MrChips

Joined Oct 2, 2009
23,524
We don't know what has transpired in previous attempts to get this working. Hence we will have to assume a worst-case scenario.

First things we will do is:

1) Disconnect all speakers from the amplifier.

2) Make sure the amp is removed from bridged mode and set for 2-channel operation.

3) Get yourself a 60-100W incandescent house lamp bulb and a bulb socket and a power receptacle, power cable and plug. You are going to plug the amp AC power cord into the receptacle. Then you are going to wire the bulb socket in series with AC LINE and the receptacle. Ask for more instructions if you do not understand how to do this. I can provide a wiring diagram if needed. You should use a switched receptacle for convenience.
 

Thread Starter

Rookieme

Joined Jan 26, 2021
44
We don't know what has transpired in previous attempts to get this working. Hence we will have to assume a worst-case scenario.

First things we will do is:

1) Disconnect all speakers from the amplifier.

2) Make sure the amp is removed from bridged mode and set for 2-channel operation.

3) Get yourself a 60-100W incandescent house lamp bulb and a bulb socket and a power receptacle, power cable and plug. You are going to plug the amp AC power cord into the receptacle. Then you are going to wire the bulb socket in series with AC LINE and the receptacle. Ask for more instructions if you do not understand how to do this. I can provide a wiring diagram if needed. You should use a switched receptacle for convenience.
Hi yes i understand that, you want me to wire it inline on the input AC , so the bulb will light should there be an AC short ?, can i have the diagram anyway please, cheers
 

Thread Starter

Rookieme

Joined Jan 26, 2021
44
Ok, this is where were at, the amp powers up but has a fault right led lit and protect led on the front lit, neither chanels give output, i have resister fuses in place of F1,F2,F3 and F4, F2 has blown, this is the +45 supto the right chanel20210127_120655.jpg20210127_121038.jpg20210127_121122.jpg20210127_121048.jpg
 

Thread Starter

Rookieme

Joined Jan 26, 2021
44
Unsure if this helps but Q26 reads dead short from bass to emitter with my meter on the diode setting, however it reads ok out of circuit
 
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