fosgate t40001bd bad p/s

[Perry Babin]

If you want to power it up directly, do so with a 15 amp fuse in series with the B+ terminal.

Larger power supplies, particularly those with multiple transformers, will draw slightly more current at idle.

 

[bdgf2004]

i have replaced all of the shorted outputs (10) but i do not have any 25w resistors. should i buy some before i continue?

 

[Perry Babin]

Have you checked all of the driver transistors and djodes in the output drive circuit?

I wouldn't power it up without the resistors. You could use 2 of the 8 ohm 25w in parallel. You can get those from radio shack.

You could try fuses (3A?) but I don't know what value would best protect the outputs.

 

[bdgf2004]

i found some 1 ohm 10 watt resistors from radio shack. i picked up 8 of em. part # 271-0131. they are 10% tolerance. will these be ok?

 

[Perry Babin]

Yes. 4 in series for each rail.

 

[bdgf2004]

ok. i'm gonna put it all together and see what happens.

 

[Perry Babin]

Monitor the temperature of the resistors so that they don't get too hot. Use a tie-wrap to hold them together. If the tie-wrap begins to melt, you know there's a problem. Also, this is only to be used until you determine if the output section is working properly (producing clean audio, not drawing excess current...). You won't be able to drive a speaker load with these in the circuit.

 

[bdgf2004]

sorry it took so long. when i got home from radio shack last week i saw one package of resistors was missing out of my bag. now i got them. the 4-ohm 40 watt resistors are not even getting warm. here is a pic of the out put (60hz wave). notice how it is a little shakey on one side. is that okay? i have not put a load on the amp yet.

 

[Perry Babin]

Without a load, it's difficult to say if it's normal. Sometimes the output filter can cause distortion like this when it's not loaded. Try it with a light load (4 or 8 ohms) and drive it to a point where it starts to make the resistors heat up. If it's clean, remove the resistors and try it direct.

When you remove power, remember that the caps will remain charged. Discharge them before touching the red and blue wires.

 

[bdgf2004]

this is at an 8 ohm load. it is turned all the way down now. before in the other pic that was right under clipping.

now i also nitice that some (not all) of the other outputs i did not replace are getting very hot.

 

[Perry Babin]

Double-check the drivers that drive the outputs you replaced. If you don't know which one they are, post the circuit board designation for the outputs you replaced.

 

[bdgf2004]

all the drivers check out ok. i only had replaced one driver originally(Q409).

 

[Perry Babin]

Which of the output transistors were replaced?

 

[bdgf2004]

Q-417, 418, 419, 420, 432
Q-426, 427, 428, 429, 433

 

[Perry Babin]

Are R416 and R417 within tolerance?

 

[bdgf2004]

with the resistors still in the circiut they both look good. i get 11ohm on 416 and 200ohm on 417.

 

[Perry Babin]

When you checked Q406, in addition to checking to see if it was shorted, did you check to confirm that both junctions were intact?

 

[bdgf2004]

i did the full check like you show in the tutorial on all 4 of the drivers while out of the circuit.

 

[Perry Babin]

Re-check all of the ES2D diodes. The damage RARELY goes back beyond the transformers so the fault is likely in this small group of components.

 

[bdgf2004]

all diodes, transistors and resistors in that area have been checked and seem to be okay. should i remove and check the other outputs that were getting hot?