hey i am fixing an Hartke amp for a friend. the initial problem was the amp turned on but no sound came out. i traced the signal to the problem ( a bad solder joint ) and fixed it.

when i went to test it after resoldering the joint, i did not but back the connector from the pre - amp to the power amp. attached is the schematic, where the connector i am speaking of is from AN104 - AN101.

now everytime i power it on, a fuse blows right away. I took out the power amplifier board and cleaned and added a little bit of new solder to every joint on that board. tested it today and the fuse still blows.

could the problem be someone in the power supply? maybe some filter cap is blown?

i have done a visual inspection of the whole amp, and nothing seems bad.

the only two things i know from here to do is test each component on the power amp PCB or test in the power supply circuity.

any help or advice is appreciated.

 

You didn't say where the bad solder joint was. It might be useful to know. The unit looks like it has connectors for most of the power supply loads. You might be able to isolate the problem to a subassembly by adding them one by one to the supply.

Start with the supply isolated from all loads and power it up. If the fuse blows, you have a power supply problem. Otherwise, turn it off, add a subcircuit and repeat the test adding each circuit until you find the bad section.

 

the bad solder joint was at the inductor in parallel with R334 right before the power IC at the end of the power amp stage.

yes. the power amp PCB has B+ and B- from the power supply to it along with a common ( i guess? ).

can you clarify your last sentence? i am confused.

 

It's a troubleshooting method to isolate the problem to one section. Since the fuse is on the P.S. which feeds all other sections of the unit and some of those sections are connectorized, you can disconnect those sections then start with the P.S. and main board on by itself to see if the problem is there. By turning it off, plugging in another section and turning it back on, you find out if the problem is in that section. You can repeat this process until the fuse blows indicating that you've just connected the bad section.

It appears that your unit only has one major section that can be disconnected so this method will be of limited usefulness to you unless you desolder some connections.

You want to make sure that all power supply voltages are being developed correctly first.

 

I'd check first all rectifier bridges on the transformer secondary (with a multimeter diode tester). Should be easy to see if something is wrong with them, as you are looking for a short circuit.

Then, as KJ6EAD suggested, try to isolate the subassemblies from the power supply. First I'd disconnect CON501 and power up the amplifier, if the fuse still blows you do the same for the other circuits/ if there are no connectors you can also take out series resistors in your power supply / cut traces where it's necessary.

The most likely though is the amplifier's power stage or the secondary bridge rectifier in my opinion.

(just to make sure: you don't live in a country with grid voltage 230V and accidentally switched the input selection switch to 120V, right?)

 

wow thanks for the quick responses and troubleshooting ideas. i will get some more fuses and start testing soon.

yes, i am in america and am using the 120V plug on the fuses and power.

 

yes, i am in america and am using the 120V plug on the fuses and power.

Ok, just to be sure, you never know...

 

hey so i just bought some 6.3A 250V fuses (lower than the recommended amperage). I unplugged CON501 (power to the power amplifier stage) and the fuse did NOT blow.

so does this tell me that the short circuit is in the power amplifier stage?