Amplifier burning resistor.

[argonrepublic]

I am guessing that the uninsulated PNP and NPN transistors were taken out by my mistake. By this diagram, does SC5200 need to insulated? There were no plastic shims but possibly in insulated coating.

 

[tauro0221]

I think it is possibly that the transistor do not required insulator. But the screw needs to be insulated. With the transistor mounted with an screw check the resistance between the transistor collector to ground. Is you have zero resistance them the screw must be insulated by a plastic sleeve. Or see if you can see metal through the hole of the transistor if you can see metal the you must isolate the screw.

 

[AndrewT]

power up via a bulb tester until you can prove that everything is finally repaired and working correctly.
Do this for all projects that you build or modify.

 

[argonrepublic]

I am about to approach this Amplifier circuit again today. What exactly should I expect with light bulb tester? I am going to assemble it today.

 

[tauro0221]

Hi,
Check this web side it will teach how to use the tester.
The Dim-bulb Radio Tester

 

[argonrepublic]

Thank you. I am getting tired of being a hack. I have done OK with repairs but OK is just not good enough.

 

[argonrepublic]

I am about to assemble my mixer. Would someone please view the full output schematic and confirm for me? I am 99% positive that there were no insulators behind the SC5200 Outputs. Does the schematic concur?

 

[llwhtt]

On that schematic the collectors of the two output transistors (2SA1943 and 2SC5200) are grounded so no need for insulators. But make sure the collectors ARE grounded, that's the middle pin. Could you please post the complete schematic? I just curious to see the whole circuit, looks similar to QSC.

Craig

 

[argonrepublic]

This amplifier has eight SC5200 the schematic may be for the 250 watt version. I will try to post whole schematic or I can email the PDF.

 

[argonrepublic]

I have reassembled circuit. There is no indication of draw however, amplifier is rated at 500 WPC @ 8 ohm. I currently have 60 watt bulb in dim light tester. Bulb is about a 3rd of 60 watt brightness. It has been on for 1 hour.
Am I safe to plug in?

 

[tauro0221]

Check the output voltage to see if everything is OKAY.

 

[argonrepublic]

I jumped ahead and plugged it in. Got sparks. I think the 22 ohm resistors blew. Fuses stayed. Am I going to suck at this forever? Maybe I should leave it to the techs or get some education. I really like working with electronics but this amp has discouraged me. Maybe this isn't the place to get emotional but I am feeling badly about myself over this amplifier.

 

[tauro0221]

Sometime this a hard way to learned. You have to smoked sometime so your learn in the hard way. It is no practical but everybody goes thought learning by sometime make smoked. Do not discourage and keep trying.

 

[AndrewT]

note that whatever was going to fail was protected by the glowing bulb. That bulb really works.
While it is glowing, or bright, you know the amplifier is drawing excessive current. THAT IS YOUR WARNING.

Don't ignore it.
measure check, find out why it is glowing. If it is due to output bias current turned up, then turn that down. recheck voltaages and currents. Has the bulb stopped glowing. Are all the voltages correct?

Only after you have convinced yourself that all is connected correctly and that all devices have the correct voltages across them do you fit a sensible fuse and direct connect to the mains.
You are simply trying to go too fast. Slow down.