Peavey 5150 t-former ??

[spiderman2812]

Okay if you've been reading my other thread heres the deal i pulled the diodes and they all tested good so i thought hey lets test the power t-former and The part # is 70500045 or e1a682 0018 there is a brown wire blue wire and a red that connect to j1, j2, j3 on the power amp schematic http://www.blueguitar.org/new/schem/peavey/5150evh.pdf and i have continuity between the brown and the red. Also from the same t-former there is a black, green white and orange that connect to the ohm selector switch for the speakers which has continuity between them all. I'm assuming that the t-former got cooked when the beer got spilled on it cuz it fried the 2a fuse in the rectifier cicuit immediately. Any input guys??

[Keystring]

Okay if you've been reading my other thread heres the deal i pulled the diodes and they all tested good so i thought hey lets test the power t-former and The part # is 70500045 or e1a682 0018 there is a brown wire blue wire and a red that connect to j1, j2, j3 on the power amp schematic http://www.blueguitar.org/new/schem/peavey/5150evh.pdf and i have continuity between the brown and the red. Also from the same t-former there is a black, green white and orange that connect to the ohm selector switch for the speakers which has continuity between them all. I'm assuming that the t-former got cooked when the beer got spilled on it cuz it fried the 2a fuse in the rectifier cicuit immediately. Any input guys??

Hi Spiderman,

I'm back from rehearsal and thought I'd jump on here and noticed this post.

What do you mean by a 'continuity' test?

Did it show any resistance at all? Or did you use the 'continuity' function of the meter. If so, then you are not going to be able to tell if the output transformer is blown with that method.

To measure it correctly, you need to proceed this way.


First thing. The red,blue, and brown wires go to the 'primary' side of your output transformer.

To test it remove all of your output tubes and set your ohm meter for as low a scale as you can. If it's digital and 'auto ranging' then it will be done automatically.

Read the resistance reading between the 'red' and the 'blue' wire and write the reading down. Now do it between the 'red' and the 'brown' wire and note that resistance also. It should read in the 'tens' of ohms range, indicating that the primary side is probably ok. If you get a 'zero' reading, or very near to it, then the transformer is fried.

Now test the output side of the trans former. The 'black' wire is common for the other windings and also grounded to the chassis. Measure the resistance from the 'black' wire to the 'green' wire and note the reading. Now measure between the 'black' wire and the 'white' wire. Keep in mind that the 'feed back loop' is connected to this winding and may give you a false reading but as long as it doesn't read 'zero' you should be fine.

Now, one more step. Take a measurement from the 'primary' side to the 'secondary' side. You should show 'infinite' or no reading at all. You can measure between the 'red' wire and the 'black' one.
If you do get a reading between these two then the transformer is cooked.

One last thing.

You say your diodes tested good. Did you pull the output tubes and try turning it back on? If so, did the fuse blow again? If it did, chances are the problem is not the output transformer but in the 'power supply' circuit.

Have you tried measuring the voltage with C34 out of the circuit?

[Keystring]

I just noticed something else in the schematic.

There are two diodes. Cr200 and Cr201. They are designed to bleed off any 'overvoltage' condition and are used to control saturation in the output stage. I would test those diodes to see if one of them is shorted. If one of them are, that would cause the 2A fuse to blow because if would cause a direct short to the Plate voltage feed.

The diodes are tied to the 'primary' side of the output transformer.

[spiderman2812]

All idi was pull the diodes and test them i figured i would check the easy stuff first. I took the readings on the t-former and heres what i've got red to blue37 ohms, red to brown 28.7 ohms. That was the primary secondary i'm not so sure it's good black to green 0.6 ohms and black to white 0.7 ohms and between the red on the primary and black on secondary i got infinite. So what do ya think I would think the secondary is no good huh? Oh by the way thanks again you're a lifesaver!!

[Keystring]

All idi was pull the diodes and test them i figured i would check the easy stuff first. I took the readings on the t-former and heres what i've got red to blue37 ohms, red to brown 28.7 ohms. That was the primary secondary i'm not so sure it's good black to green 0.6 ohms and black to white 0.7 ohms and between the red on the primary and black on secondary i got infinite. So what do ya think I would think the secondary is no good huh? Oh by the way thanks again you're a lifesaver!!

From those readings I would say it's fine.

From my statement above.

"Now measure between the 'black' wire and the 'white' wire. Keep in mind that the 'feed back loop' is connected to this winding and may give you a false reading but as long as it doesn't read 'zero' you should be fine."

I would check the two diodes (cr200 and cr201) to see if one of them are shorted.

My suspicion is that there is a problem in the power supply section, but one of those diodes being shorted can pop the fuse as well.

I would go back and pull C34 and power the amp up and measure the voltage from the rectifier and then go from there.

It can be a fairly pain staking procedure, but the best thing to do is go one stage at a time.

Hope this helps.

BTW.

You don't need to pull those diodes as long as the power tubes are out.

[spiderman2812]

I forgot to mention that i measure the voltage on the rectifier circuit and it was over 120v without the standby switch(after the diodes) on which shorts the 2 a fuse.
I measure bwtween the white and black and got 0.5 so i assume its good. I kind of agree that its in the power amp circuit cuz that's when the problem occurs is when the standby switch is engaged. Also that is the area where the beer was spilled in the head. I have to desolder all of the tube sockets to get it out so i can see the parts that are in the circuit so i know what i'm testing i might try to trace it out but i think the board probably needs cleaned up to from the beer. I can't believe they would rivet that dang board to the housing so you can't get it out without desoldering the tube sockets but i guess thats there way of trying to get you to send it to them ya know?
This could possibly take a little time and i don't know if i'll get to it today so i'll keep ya posted when i get the board out. Thanks again.

[Keystring]

I forgot to mention that i measure the voltage on the rectifier circuit and it was over 120v without the standby switch(after the diodes) on which shorts the 2 a fuse.
I measure bwtween the white and black and got 0.5 so i assume its good. I kind of agree that its in the power amp circuit cuz that's when the problem occurs is when the standby switch is engaged. Also that is the area where the beer was spilled in the head. I have to desolder all of the tube sockets to get it out so i can see the parts that are in the circuit so i know what i'm testing i might try to trace it out but i think the board probably needs cleaned up to from the beer. I can't believe they would rivet that dang board to the housing so you can't get it out without desoldering the tube sockets but i guess thats there way of trying to get you to send it to them ya know?
This could possibly take a little time and i don't know if i'll get to it today so i'll keep ya posted when i get the board out. Thanks again.

120v??

That's way to low if that's on the secondary side of the power transformer.

It should be 450volts or more.

Are you sure you aren't reading the 'primary' side instead because the 'line' voltage should be about 120 volts.

When you say you turned on the standby switch and the fuse blew, is that with C34 pulled and the B+ line disconnected from the rectifier?

Something doesn't sound right here.

[Keystring]

Ignore this post.

Read below..

[Keystring]

Ok.

I've been studying the schematic and the first thing we need to do is run down a check list.

1.) check the 'bias' fuse (F5) and see if it's blown. If it is then replace it.
If the bias fuse is blown then there will be no 'negative' bias and your output will run wide open and cause the main fuse to blow or possibly cause a short in the power supply section. Not to mention it can fry your tubes.

2.) leaving everything connected, minus the output tubes, leave the standby switch off and power the amp up.

3.) measure the voltage at C34. It should read 485 volts (or thereabouts)

4.) Read the 'screen' voltage. You can do that at the 'standby switch or the plus (+) side of C35. It should be about 475 volts. If the reading is way too low then suspect the power transformer is shorted.

If those voltages check out then turn on the standby switch and see if the fuse still blows.

Once you've done this, then we can get a better understanding of what's going on and proceed from there.

[Keystring]

I found a different schematic that shows the output section better.



The first thing you notice on the schematic is the 'standby' on the bottom that sits between the 'Plate' and 'Screen' voltage points.

If you look above that you'll see CR200 and CR201 which I mentioned earlier.

A simple conclusion here would be that when you turn on the standby switch, and it pops the main fuse, that one or both of those diodes are shorted because the 'Plate' voltage is switched on and the diode(s) are causing a direct short to ground. Since we've already ruled out the output transformer then the diodes being shorted would be the next logical conclusion.


Might want to check them before you take the amp apart too much

.

[spiderman2812]

I desoldered the tube sockets and pulled the board to the power amp and the diodes read about 1.6 or so on diode test. Everything else seemed to check out resistor and capacitor wise so i'm going to resolder that back in after i clean it up and we'll power it up and do the rectifier circuit tests with c34 that you were talking about. I'll tell you what if i ever get this fixed I'll know this amp inside and out!! Could it be possible that the main transformer on the 120 preamp board the one that has the power cord connceted be shorted? I guess it's worth checking but the amp fires up and comes on and the tubes even start to heat up it's when you kick the standby switch on. Let me know what you think. Oh i already know check the rectifier circuit right!! lol (hahaha) just a little sarcasm.

[Keystring]

I desoldered the tube sockets and pulled the board to the power amp and the diodes read about 1.6 or so on diode test. Everything else seemed to check out resistor and capacitor wise so i'm going to resolder that back in after i clean it up and we'll power it up and do the rectifier circuit tests with c34 that you were talking about. I'll tell you what if i ever get this fixed I'll know this amp inside and out!! Could it be possible that the main transformer on the 120 preamp board the one that has the power cord connceted be shorted? I guess it's worth checking but the amp fires up and comes on and the tubes even start to heat up it's when you kick the standby switch on. Let me know what you think. Oh i already know check the rectifier circuit right!! lol (hahaha) just a little sarcasm.

If CR200 and CR201 test ok, then the next step would be to look for a shorted capacitor in the 'bias' section.

C41 would be the most likely culprit. If it shorts that will pull your B+ down and blow the fuse as well.

Once you get the amp back together, you can measure the Secondary voltage for the power transformer even with the 'standby' switch off.

It should read as I indicated above. If it's low, then the power transformer may be shot. But since you said that the heaters began to glow, that tells me that at least the heater taps are ok.

As far as the transformer on the preamp board being shorted. I would say no.

That is really nothing more than a line filter. Not a power transformer. It wouldn't effect the power circuit.

When you get it back together take the power readings and we can go from there.

[Keystring]

"Oh i already know check the rectifier circuit right!! lol (hahaha) just a little sarcasm."

Well, it's good that you've got a sense of humor cause sometimes these things can be a real pain. Especially with everything I've read about the 5150 and the nightmare it can be to work on.

Better you than me!

[spiderman2812]

HA HA !!! very funny

[spiderman2812]

Oh by the way it doesn't pop the main fuse it pops the 2a fuse at the rectifier circuit