Blown Rivera Hundred duo twelve, please help

[jezzbo]

Hi Guys,

A friend of mine asked me to look at his blown Rivera Hundred duo twelve.

It would be great if you guys could help me a little with this.

My friend used his amp during a show.
As I understand there was virtually no airflow at the back of the amp.
suddenly he says there was smoke comming out of his amp. (near the PT)
he shut down his amp immediatly.
So I assume the amp simply overheated because there was no airflow.


Facts.

1. During a show, there was virtually no airflow in the back of the amp.
2. Smoke came out of the amp near the PT
3. Amp smelled burned.
4. immediately shut down amp.

On visual inspection:

1. There are white spots on the bottom of the amp cabinet.
Under the PT (image 1 & 2)

2. There seems to be some white stuff at the PT (image3)

On opening the amp:

1. A 1000uF 35V elko blown (image4a, image4b)
The guts of this cap are all over the place.
This cap in circuit of the 24V supply.

2. One fuse 1,6A 250V of the B+ blown (image5)
The other fuse is intact.

3. H.T. fuse not blown. (values are correct, 250V 1A)
4. main fuse not blown. (values are correct, 250V 2A)

5. One elko 330uf 250WV (Nichicon) blown. (image6a, image6b)
There is a hole near the bottom of this cap.

6. One cap of 0.01uf 440V accrues the 2 poles of PT for B+ (before rectifiers)
Looks funny, It seems to have a tummy. (image7)

7. The red wire that goes from the standby switch and go's to the mane board looks burned.
The isolation has some black in it and it feels harder than the other wires. (image 8a and image 8b)

Resistors at the powertubes seems to be ok.
The look normal and measure normal.
1K (5W) and 2,7K (1/2W)


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Questions:

1. What should I check next?
2. how do I know when the OT and PT still work fine?
3. I assume that the amp overheated.
4. does that mean that the powertubes are gone to?

For pix please click on this url. there is also a schematic of the amp.
Not that good readable but this was all I could find.

[/url] http://users.telenet.be/jezzbro/rivera/

Thanks for your help!

Jesse

[martin manning]

Hi Jesse,

My next move would be to disconnect all of the PT secondary leads and test to see that all of the primary and secondary windings are isolated from each other and from ground by measuring resistance. The ones with fuses can be disconnected by pulling the fuse, the (7) others will have to be un-soldered. If all windings are isolated, then you can apply power to the primary and measure the voltage on each secondary. If they all check out, then the PT is OK.

The blown fuse on the B+ could be caused by the bulged 0.01 cap shorting. This and/or a short in the 1000uF cap could have increased current draw to the point of overheating the PT, causing an internal short.

F1 is the mains fuse, F2 and F3 (on the B+) are HT fuses, and the other one (F5? it's hard to read) is on the filament winding, but located on the output tube PCB according to the schematic.

MPM

[jezzbo]

Hi Martin,

thanks for your reply.
I was thinking on measuring the PT but needed a second opinion.
Thanks for that.
I'm gonna de-solder the pt and measure.
I'll keep you guys posted.

Jesse

[jaysg]

In a Rivera, the heaters are run off of the 24V power supply. A bad tube may have been the culprit. I would guess that the taps for the 24V supply could be shorted internally and the PT may be shot. Disconnect those too for testing. A 7818 may have died and you won't see it. ymmv

[jezzbo]

In a Rivera, the heaters are run off of the 24V power supply. A bad tube may have been the culprit. I would guess that the taps for the 24V supply could be shorted internally and the PT may be shot. Disconnect those too for testing. A 7818 may have died and you won't see it. ymmv

I wonder how I could test those 7818's.
If the PT is ok and I replace the filtercaps, can a bad 7818 ruin the 1000uF 35V again?

thanks

[jezzbo]

Ok guys,

I've just disconnected the PT and meassured it's secondary windings.

orange - orange wires = 43V
Red - red wires (not to centertap red/white) = 338V
grey - grey (not to centertap grey/white) = 40V
Green - green = 6,55V

To me that seems allright.
What do you think?

When I switch on the amp I can hear the PT hum (and actually feel it slightly)
I asume that's ok?

Can anybody please tell me how I can make sure that the OT is still working as it should? is there some sort of test?

Thanks!

[jaysg]

If you run the PT open ended like that, and it has internal shorts, it will heat up drastically in 3 to 10 minutes. If it stays cool, then you're probably okay. Assuming you've removed the bad cap and any other obvious components, then you need to see how the power supplies function without any tubes installed.