Peavey Classic vtx series- Troubleshooting repair help needed!!!

[oc disorder]

So its looking like faulty diodes ..the fuse is 500mA ? just quickly swap the two tubes and measure
at pin 5 again..see if the 5 volts stays with the tube or the socket.
Having done that lets check the first port of call and measure the AC voltages before it turns into 525DC.

[marley]

Yes sir, the fuse is a 500mA. I swapped the tubes and the 5 volt measurement stayed with the socket. I assume that is normal.
Now, onto the ac voltage.
The wires that are along the edge of the power board (as in your diagram) are 3-orange, 3-red, and the last 2 are yellow. I am unsure how to measure each one of these. Do I keep the ground from my m.m. on the chassis ground and test G, BK, and R with the red probe. Or is BK the ground for G and R? Brian

[oc disorder]

To measure these ac voltages simply connect to the ac wires.
For some practice set mm to AC volts put one probe on yellow wire and the other on the other yellow wire ..you should read 6.3 volts approx.
As it is AC there is no + or - for measuring purposes.
When you have 3 wires coming from a transformer one of them should be marked with a stripe to show it's the centre tap. (Otherwise one of them should read the same with respect to the other two).
Now on the orange wires or low voltage supply for the pre-amp between the left one and the centre one (should have white stripe) should be approx 20volts AC.
Likewise From the centre wire with white stripe to the yellow one on the right
should read 20v AC.
Therefore from the two outer yellow wires you should get approx 40v.
We know that this supply works as the pre-amp works ... the voltages are my guess's and are only approximate.
So now we measure the HT or red wires the same way. Outside to centretap x 2approx 200v AC then outside to outside approx 400v.

The two pin 5 voltages should be the same but lets leave this for the moment 'till
we get the HT going.

[marley]

Ok, I got the ac measured and all looks good.
The 2 yellows are at 6volts
The low voltage(orange) measured 20 volts each and 40 together.
The high(red) voltage measured 185 volts each leg and 370 volts together.

Does this point to the diodes even more, now? Thanks again for walking me through this. Brian

[oc disorder]

Good. As the heater measures 6 volts I presume this was measured with the tubes in ?
If not try it (by the way with tubes in should really have speakers connected ).
So now you can measure 370 volts AC going into a bridge rectifier and 2 volts DC coming out..maybe 34volts on a good day!

It can't be a heavy load or short circuit on the DC out as the 500mA fuse would normally blow.
Therefore all the solder joins ,pc tracks, components,and connections including the fusehave to be checked as it appears there is a very high resistance somewhere.
Actually something is staring me in the face.
It's the chassis ground side of the HT supply which is also the ground for one side of the heater supply and CR31 and CR38 at the tube sockets.
It seems from the layout of the power supply there are three wires that go in a connector to the Tube Board which we don't have a layout picture of .
They are the HT 535v wire ,the combined ground and heater wire and the other heater wire.
The "combined ground and heater wire" should end up connecting to the chassis , one pin of the tube socket and the grounds of CR31 & CR38 at the tube board.

Check thats the case ..if you have a continuity "beeper" in your mm one probe on the second heater winding from the right on the power board and the other to the chassis , should show connected or on ohms scale a very low reading.
When checking that earth connection may be less confusing to remove the tubes and heater fuse.

Check the fuse holder F1 and fuse for any corrosion or oxidation - rub with emery /fine sandpaper if necessary check the soldering underneath and the solder plated copper tracks for any hair line cracks.Especially check around the diodes CR1,2,3&4 .
If you look closly at the diodes you may see a small crack or rupture (hopefully !) .

Were you able to do this ?

If you have a diode test function let the amp discharge for a few minutes (if the transformer unplugs from the power board unplug it or remove the HT fuse) switch the s/b to centre position and measure each diode Cr1,2,3&4.
The diode test function should show a reading one way (.5?? to .8?? approx)and no reading the other.

Well maybe for the cost $1.30? you could buy 4 x 1N4007 diodes and put them in.

Note the stripe on one end.

With the amp off and discharged - check either with continuity "beeper" or a low ohms setting all over that power board to see that all the tracks and connections are ok.
Bear in mind the transformer windings will give a very low reading as will the heaters if the tubes are plugged in.
I would pull out the fuses and say.. check between the cr2 lead and the cr4 lead and see if they are joined together as they should be via that track.
Check from there to the fuse holder end they are supposed to be connected to etc.

[marley]

I am still here, just been under the weather lately. I have not had another chance to go over the power board to check for solder issues and my mm does not have a diode test function.
I wanted to let those, that have helped with this problem, know I have not given up on this yet.
I will report back when I check the p. board again.
I will also check the 3 wires coming from the p. board going to the tubes.
Thanks again for the help and the patience. Brian

[marley]

Ok, I have checked the power board for any cracks or signs of trouble and do not see anything.
The 3 wires going to the tubes/tube board are all where they should be as well as chassis ground.
I do not have a diode tester.
I checked all the fuses and everything looks good with those.

I was really hoping to see a problem with one or more of diodes, but there is nothing obvious with any of them. I may just order these and hope for the best but I would like to be sure.

It is about time I wrap this thing up fixed or not, it has taken up too much space on the living room floor.

If there are any last words of wisdom, I would like to hear them. Thanks again for all the help (especially oc disorder) Brian.

[oc disorder]

replacing the lost pics from the forum crash in case they are of any use.
Interestingly the forum wont accept the jpegs re posted even with a name change !
Converting the image to gif allowed them to stick !

[g1]

Interestingly the forum wont accept the jpegs re posted even with a name change !

It's not the name that matters, but the type (jpeg) and exact file size in bytes. So if you added a dot somewhere in that jpeg, it would probably change the file size enough that it would stick. For pdf's, I find re-saving them and overwriting the original changes the size. Also zipping a file and posting it as a zip usually works.

[Jazz P Bass]

Here are the files that OC posted.
Zipped/ pdf.