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#1
I was hoping to figure this out on my own, but I'm out of ideas.

I tried installing a fan in the (had been assumed) 6.3 volt pilot light connections that lights up the logo on the amp. Black to black, red to red. The fan spun for a second, then stopped. When the amp was turned on from standby, I get a buzzing, even with the volume all the way down. And the channel lights don't illuminate, neither does the logo when plugged back in.

I checked the tubes and everything glows okay when the amp's in standby, But when I turn it on, the output tubes glow a brighter-than-normal blue and start red plating.

I know this is very hard to help with over the internet but any input is great. I know a bit when it comes to amps (lethal voltages included) and want to fix it myself rather than take it to a tech.

Thanks a ton for any help and sorry for the huge post. I can provide any pictures necessary.

EDIT: one of the coupling capacitators has what looks like a split of some kind (really just a bit of a black mark) I'll get a picture up asap.
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Last edited by metalhead352 at Apr 6, 2012,
#2
I've heard of potential for fuse blowing on the LED circuit, but haven't had this problem so I can't tell you where it is. I'd check for a blown fuse first. Btw, why did you install a fan...I imagine that would draw more current than the LED circuit is designed to handle.
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#3
Oooops. Maybe you killed the diode rectifier bridge? Most amps have that shared with the heater grid(lighting circuit that is).

Like stated above check fuses and get some pictures of that cap you mentioned.

Red plating tubes is not a good thing.

Do you have a multi meter?
Last edited by R45VT at Apr 6, 2012,
#4
No blown fuses unfortunately. And when I put the fan in the led circuit I had been under the assumption that it was a 6.3 volt circuit that could power the fan. I had been powering two off one 9 volt battery so I thought one would be fine.

here's the cap, It doesn't look that bad but it's the only semi-obvious physical clue I can find.

I do have a multi meter, and the resistor that is supposed to control the bias doesn't seem to be reading the right value (4.7) although that could very likely be my somewhat cheap multimeter and/or my inexperience using it.

here's the melted gel too.

those wires are right next to one of the filter caps. Not sure if that makes any kind of difference.

EDIT: sorry for the large pics. and thanks again for the replies.
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Last edited by metalhead352 at Apr 6, 2012,
#6
I know I'll sound like an idiot for saying it, but I honestly don't know, I'd assume it was dc. I'm not sure how to find it out either. Would I touch the leads of the multimeter to the connections for the leds?
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Last edited by metalhead352 at Apr 6, 2012,
#7
For your LED wiring yes, however I would suggest being very careful as something is not right inside your amp.

You would have to hange the AC DC setting to measure each. I have schematic at home I believe. It may have a spec listed past the diode bridge.
#8
Alright I'll check tomorrow morning and let you know. And I've been extra cautious, thank you.

And are you saying there's both ac and dc voltage going to the leds? or am I misreading this?
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#9
No- and I must say I am going off of memory here that the combo was diode rectified as opposed to tube for the heater.

If you have 6v dc I would be shocked. If you g
Have AC then you probably killed the rectifier, which is if I remember correctly a diode bridge on the 112 combo.

I am typing this from an airport so tomorrow, time permitting I will try to look it up to let you know for sure.
#10
Well, I checked the led connections today, and got no readings. I did get something on continuity but that's it.

And I know it's solid state rectifier if that's what you're saying R45VT, or at least there's no rectifier tube. (hope I'm thinking of the right thing) I might be able to post a schematic for it if that helps. But are you saying there's a bad diode in the amp? or is their an entire rectifier i need to replace?
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#11
http://www.flightlessamps.com/Schems/Peavey/6505-112.pdf

Here's a schematic for your amp. For some reason it looks like the backlight has a 30v power supply (I skimmed the schematic). However, the actually backlight circuit isn't shown in the schematic.

You have 6.3v DC for your preamp tubes, but 6.3v AC for you output tubes and phase inverter.
#12
Lower left corner of the schematic ^^^

Uh oh.... Ok- it's a diode rectifier bridge- 4 diodes that control the power tube bias, 2 of them control backlit PCB. Not thing you wanted to blow up.

Find diodes 4, 4, 14, 15. These are the rectifier bridge diodes. It's supposed to be 15v past the bridge, C50 and C51 are involved as well- what number was the capacitor that looked ****ed?
Last edited by R45VT at Apr 7, 2012,
#13
Quote by R45VT
Lower left corner of the schematic ^^^

Uh oh.... Ok- it's a diode rectifier bridge- 4 diodes that control the power tube bias, 2 of them control backlit PCB. Not thing you wanted to blow up.

Find diodes 4, 4, 14, 15. These are the rectifier bridge diodes. It's supposed to be 15v past the bridge, C50 and C51 are involved as well- what number was the capacitor that looked ****ed?



I'm still seeing the actual backlight circuit, just the power supply for it.

Diodes D3, D4, D5, D14, D15, D16, and D17 are all associated with the bias. (More emphasis on 3, 16, and 17 for bias).

The messed up looking capacitor is just the coupling cap into the final gain stage. It wouldn't have anything to do with backlight, but could explain the buzzing.

EDIT: Also, C23, C64, as well as C50 and C51 are involved in the backlight. C6, C7, C16 and C24 are with the bias circuit.
Last edited by end_citizen at Apr 7, 2012,
#14
I'm no expert, but 30v seems like a ton for just 6 leds... Or is it just me? (thanks for he schematic btw end c) So if I do want to install a fan later once this is fixed, I would run it off the power for the preamp tubes? Or do you guys think this would be too much?

And the cap in the picture is number 57.
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#15
Quote by metalhead352
I'm no expert, but 30v seems like a ton for just 6 leds... Or is it just me?

So if I do want to install a fan later once this is fixed, I would run it off the power for the preamp tubes? Or do you guys think this would be too much?

And the cap in the picture is number 57.



I agree 30v is a bit much for 6 LEDs. That's why I was trying to find their circuit. (Just found it sort of). There are +15 volts supplied to certain diodes and -15 applied to others with the appropriate resistors.

If you run it to the LEDs, you're also running the fan through that LED's resistor. Either run it off a +15v to ground (if it can handle 15v) or run it from +15v with its own resistor. Possibly bad advice. The voltage regulators are rated at 1.5amps. I don't know the current draw of your particular fan. 6.3v supply may work better for the circuit.

The cap is associated with the final gain stage before the phase inverter. I don't see how you could have damaged it, but I'm not ruling it out yet.
Last edited by end_citizen at Apr 7, 2012,
#16
So I would be better off running it off the preamp tube power? It was a regular 12v dc fan, that also seems to have been fried.

And I'm not positive the cap is even damaged. As I said earlier my testing equipment isn't exactly top notch. Nor is my knowledge of using it.
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Last edited by metalhead352 at Apr 7, 2012,
#17
Can you give me an idea of what your testing equipment is? A pic would help. That way I can give more specific instructions.

Also, unplug the amp from the wall if you haven't already.
#18
Number one


And number two


They both seem to give different readings when it comes to continuity. The small black one will measure some resistors like they arent there and the green one will measure as if the probes were stuck in a block of wood.
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#19
The larger one has a diode check feature. That's good news!

Check your diodes that were mentioned earlier- they should forward bias in one direction an not the other.

The analog meter draws more current than the digital, both have their application but don't use the analog on low current circuits.
Last edited by R45VT at Apr 7, 2012,
#20
Good that the digital one has a diode setting. This will be important. I don't have either of those exact meters, but I've got some that are close.

Part of the reason you see different readings is because the scales are different. The black analog one only measure in the 1's scale. Meaning if the resistor is 10 ohms, it'll show 10. If it's 1 million ohms, it won't move.

The green one reads in the 1's, 10's, 100's, 1000's, and 1,000,000's. You've got to have it on the right scale to display a more accurate reading.

This is the resistor color code chart. All you should be concerned with in regards to your green meter is the color of the second to last stripe. For instance, R92 from the picture above. There are 4 stripes. The gold one is the "last" stripe, the red one is the "first" stripe. So you have Red, Red, Yellow, Gold. That would be 2, 2, 4. The first two are the first two numbers. So we have 22. The yellow stripe is the number of zeros to put after that. So we have 22 with 4 zeros behind it or 220000. That is 220,000 ohms (or 220k). You'd set your meter to the 2M setting. The 2M means it can read at most 2 million ohms on that setting. The 200k setting means it can read at most 200 thousand ohms on that setting.

http://www.elexp.com/tips/clr_code.gif


Alrighty. That's the resistors. Now on to diodes. Diodes allow current to flow in one direction. If they go bad they'll either prevent any current from flowing or allow current to flow in either direction.

Here is a pic of the meter I have closest to yours. I used clips on the diode to get a picture, but they are completely unnecessary for what you'll be doing. You need to set your meter to diode and make sure you get a reading in only one direction. For my meter you have to put the negative lead on the side with the stripe. The positive lead must go on the non-striped side of the diode. It may be reversed for your meter. If you get a reading in both directions, you may have an issue. Grab a piece of paper and test diodes D3, D4, D5, D14, D15, D16, and D17. The paper is just so you can keep track of how each one tested.

#21
That explains a lot actually.

And as for the resistor i was questioning, I'd orignally tried every setting on the green one. And none of them seemed to make a difference...
EDIT: retried it, again went through all the settings and didnt get anything. Same thing on r67.

And all the diodes mentioned function the way they should.
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Last edited by metalhead352 at Apr 7, 2012,
#22
Let me make sure I have the symptoms right:

1. Constant buzzing noise, even with volume all the way down.

2. Output tubes are red plating.

3. None of the LEDs are working.

Did I miss anything?
#23
Quote by end_citizen
Let me make sure I have the symptoms right:

1. Constant buzzing noise, even with volume all the way down.

2. Output tubes are red plating.

3. None of the LEDs are working.

Did I miss anything?

Dead on the Money.
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#24
Alright, the next thing I'm going to ask you to do will require you to be very careful. I don't want you getting hurt. If you have some leather gloves, I'd put them on just to be safe.

Remove your output tubes and your phase inverter (V5).

You won't need to plug a speaker into the amp because there is no load on the primary side of the output transformer.

Turn the amp on (you don't have to take it out of standby). With your meter set to AC voltage, measure the AC voltage across C75 (place red on one side, black on the other - nothing goes to ground). (Meter setting is ~V200)

Then I need you to set your meter to DC voltage. Keep the black probe to the chassis to ground it. Then check the DC voltage coming out of C50 and C51. There should be a yellow and a blue wire near them. The yellow is C50. The blue is C51. (Meter setting is DCV 20)


Finally I need you to measure DC voltage at where R73 and R74 meet. It should be a negative voltage. (Meter setting is DCV 200)

Then turn off your amp, unplug it, and wait for capacitors to discharge while you give me the readings.
#25
Before I go doing this (and thank you very much for the concern and safety precautions. Would rubber soled shoes help? or just overkill?) I'm Still not positive as to which side of my meter is dc, and which is ac. Is the bottom right green settings (not uf) dc and the top left ac? Just looking to be sure.
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Last edited by metalhead352 at Apr 7, 2012,
#26
Here is your AC and DC volts (The V on there is Volts. The ~ is ac. The dashes and dots is DC.)



Also, R73 and R74 don't meet in an obvious place. Just measure DC volts on both sides of R73 and R74.


EDIT: Rubber soled shoes would keep you from getting shocked through to ground, but if you are touching the amp while you get shocked, you'll get shocked through to the chassis.
#27
Alright thank you for clearing that up. I'll be back in a little while with the measurements.
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#28
Before I plug anything in, I looked over your instructions and looked at the amp, and there's two yellow wires connected to the board. Are these the right ones and does it matter which one is tested?

EDIT: just checked c75 and got no reading at all. The meter flashed a negative sign before the zeros but thats it.
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Last edited by metalhead352 at Apr 7, 2012,
#29
Take a picture if they aren't marked. There should be a yellow "PBL+" and blue marked "PBL-" They might be near C50 and C51, but I'm not positive. There's a good chance of there being several yellows and several blues. So the chance of the two yellow wires being the same are very unlikely.
#30
Well, the only realy blue and or yellow wires I can see are those connecting to the power and output transformers.
Would a shot of the whole chassis and area help?
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#31
It couldn't hurt as long as it is high enough resolution.

Also, the blue and yellow wires should be going to the backlight. If you see blue and yellow wires headed in that direction, the pics might be unnecessary.
#32
Found them. I was looking for physical colors, They're red and black on mine but they're labeled that way on the board. The only problem is that they're underneath the yellow paste. Would removing it cause any harm?

And thank you again for helping so much. I really appreciate it.
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#33
No problem. My weekend plans are to do homework for hours on end. This is much more interesting to me.

Removing the yellow glue shouldn't harm them as long as you are careful, but are the glued on the other end as well? As long as you can measure voltage it doesn't matter which end of the wire you're at.
#34
Haha, glad I gave you something to do then.

And the other ends arent covered, so I'll go test and let you know soon.
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#36
Zero!? Is the amp even coming on? Is there a fuse blown somewhere? Check F3 and F4. If there is continuity across the fuses, then you're good. But there's a good chance you just blew a fuse. (Can't believe I didn't tell you to check this first)
#37
Well, in the respect of tubes, everything comes on and glows on standby, powertubes redplate when standby is turned to on. But the leds indicating channel don't come on. channel switch doesn't seem to do much either. I'll retry in a minute since that meter didn't start reading anything on the diodes until I smacked it a bit.

By remove the output tubes and v5, you mean just the tubes right? And not the entire socket? Since I just took out the tubes.

And all fuses are intact.
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#39
Alright then.

And yes they all are. All the tubes glow fine on standby.
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#40
Then there is definitely voltage there. Make sure the leads on your meter are securely pressed into the meter.


EDIT: Oops. Slight lie there. Got my circuits mixed up. This doesn't mean that the +/- 15v circuit is working. Check AC voltage with Red probe on left side of F4, black probe on left side of F3.

Then check AC voltage with Red probe on right side of F4, black probe on right side of F3.
Last edited by end_citizen at Apr 7, 2012,
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