Marshall MG100HDFX - No sound

[Rotus623]

Do you guys think that the issue may be a little further in the circuit, like maybe on the output jack PCB instead of the output IC board?

 

[llwhtt]

Try removing the TDA7293 from the output PCB and then reconnecting the PCB WITHOUT the TDA7293 and see what happens. If it does not blow the fuse the IC has to be the culprit. The output of the IC goes to the speaker jack, with the TDA7293 still removed check for continuity between the HOT and GND on the jack, there should be NO continuity. As far as replacing the IC or the whole module that's up to you, I'd hate pay all that money for a module that only has a bad IC. One more thing, check the main board very carefully for burned parts, especially the parts to and from the output IC, first page upper right corner of the schematic.

Craig

 

[Rotus623]

Sounds like a plan.

 

[Rotus623]

So I did what you asked, Here are the pins

1 Standby
2 Inv. Input

 

[Rotus623]

3 non inv input
4 signal grnd
5 clip and short circuit detector
6 bootstrap
7 +vs
8 -vs (signal)
9 standby
10 mute
11 buffer driver
12 bootstrap loader
13 +vs power
14 out
15 -vs power

Here is what showed continuity
1,2,3,4,7,8,9,10,13,15

When I checked the output (14) my continuity tester struggled to make a beep, (with no IC in place) which means to me that there is an itty bitty short somewhere in the output section. ? is, do I start looking for a short before the power module, after the power module, or at the power module itself.

Also, the TDA seemed to short out right under pin 9. Obviously all of these measurements were taken without the TDA in place.

 

[Rotus623]

I am afraid to get a new $25.00 power module just to fry it. Do you think the problem is elsewhere from these findings?

 

[Rotus623]

Thanks again Craig. I found a tiny little short on one of the switches on the amp. When I fixed it, no more fuse blowing. Thanks again!!