MTX Thunder 6152 issue

[gsg529]

Trying to fix for a friend and do not have much history on it. Here is what I know so far:

1. Amp powers on fine, however, I have not tried to connect any speakers or line level signal yet because....

2. There is a visible component that is blown on the main board - it is D93, so I figured I would start here first before proceeding any further.

a. D93 looks to be a capacitor but I am not sure - can anyone confirm
b. Does anyone have a schematic for this amp they can forward, or, since D93 is the same as D601, 605, 606 & 607 - can anyone tell me what the value of this component is or how I use the codes to find a replacement?

 

[Perry Babin]

Can you post a photo of the area where the diode is located?

Do the other diodes have ES2D printed on them?

 

[gsg529]

D93 Photos

The photos are not that clear, but the area around D93 is charred, particularly the cathode terminal from what I can tell. Yes, ES2D is printed on them.

 

[Perry Babin]

With the diode removed, if the cathode pad is directly connected to the RCA shield and the anode pad is directly connected to the ground terminal of the amp, don't replace it. With that diode in place, if the ground connection for the amp is lost (or weak), the amp will try to ground through the RCA shields which could be a fire hazard. There should be a 1k ohm resistor and another diode connected in parallel with that diode, if it's like other MTX amps. The other diode will be connected with the opposite polarity.

 

[gsg529]

Diode is removed and cathode pad was not even attached when trying to desolder - the pad is burnt off of board. Anode pad is in tact. Cathode end connects to R23 (1K ohm) and that trace is broken due to burnt pad. There is not another visible diode in that area that I can see. Diode itself appears to be burnt - when tested out of circuit with MM, getting beep in both directions.

MM Ohm tests returned:

- Anode to GND: 1K
- Cathode to GND (via R23 trace): 0.3 - Cathode appears to connect directly to GND

 

[Perry Babin]

What does it read from the anode to the RCA shield?

 

[gsg529]

Anode to RCA shield is 0.3

 

[Perry Babin]

This amp was produced after they found that the other diode could cause problems. There's a good chance that 12v contacted the RCA shields and that's what burned the trace (and diode, if it's defective). The amp should work with this diode out of the circuit. The 1k resistor needs to be in the circuit. Confirm that one end is directly connected to the RCA shield and the other end is directly connected to the amplifier's ground terminal.

 

[gsg529]

OK. I will verify what you mention w/o D93 installed.

If I wanted to put a non-SMB diode back in circuit (due to the pad issue), could I use a tube style diode such as an 1N5402 or 04? I'd connect the anode lead to the anode pad, the cathode lead to both R23 and the RCA shield directly.

 

[Perry Babin]

Virtually any diode will work in that location.

 

[gsg529]

The resistor tested out as described. I'm going to put a jumper in place to reconnect R23 and test for sound. I'll replace the diode after and re-test. If something else comes up, I'll let you know, but I'm suspecting that it will be good to go. Thank you in advance for your help Perry!