5150 Combo Chassis

[sweatyk]

I'm trying to remove the main pcb's to inspect for bad solder joints. I have everything removed that would hold it in. Obviously it is not going to come out very easily. If the pots were about an 1/8" shorter it would drop right out. Any suggestions as to the best way to get it out? It doesn't lack much but just enough to make me start drinking again.....lol. GRRRRRRRRRRRRRRRRRRRRRRRRRRR

[Enzo]

It is arranged like a Classic 30. The boards form a three sided structure. If there is a jack board in the way, pull it out, but we then bend the sides towards one another. Push the socket board towards the controls board. Collapsing the three sided bit this way allows more clearance.

[sweatyk]

I finally got it out. My post was pre-coffee. I realized that the jack board had to come out. Upon investigation all solder connections look pretty good. A sketchy one on C30 but that's it. The symptoms are when you switch it from standby to on it has this distorted cascading wave for a second or two. The sound is low and can only be adjusted by the pre volume on both channels. Both post volumes do nothing and the tone is all treble with no mid or bass. Does this sound like a classic symptom? A few months ago it kind of gave me a small preview of these symptoms. I deoxed all of the tube sockets really good and it seemed to have cleared up so I thought. Any recommendations or where to start? Visual inspection did not turn up anything obvious.

[Jazz P Bass]

I would suggest that you start with the power supply.
Check all nodes for excess Vac ripple (especially the preamp).

[Enzo]

And isolate the problem. You have FX loop jacks, so determine if the problem is before or after that point. Essentially is it the preamp or the power amp.

[sweatyk]

Thanks guys.....while I have it apart and access I'll clean al the pots, jacks, and tube sockets thoroughly. Then put it back together to start troubleshooting.

[sweatyk]

When I plug the guitar into the FX return there is no sound. With that in mind where do I start with troubleshooting? OT?

[Enzo]

Are all tube heaters lit? Are all power supply voltages present? Is there really ZERO sound or is there just no audio, but there is a small background hum or hiss?

[sweatyk]

The tubes are lit, no hiss or hum that I can hear. I'll check the power supply voltages once I'm home.

[sweatyk]

If I'm doing this correctly here is what I have tested so far.......Please correct me if I'm wrong. On the jumper ribbon from the power pcb to the output pcb I measured the following voltages..

J125 & J126 = +26 VDC
J127 = -2.5 MV
J128 = +493 VDC
J129 = +500VDC

If I read the schematic correctly it should be J125 & J126 = 440 VDC, J127 & J128 = 300VDC, and J129 = 280 VDC.

Is that correct on my account?


peavey_5150_combo.pdf

[Enzo]

Hi.
There is nothing wrong with your approach, you are just not using the same points I would. But it would help if we wrote J25 instead of J125 if we refer to the schematic. I realize PV drew the layout with those numbers but the schematic with the others. I looked high and low on the schematic until I figured out what was going on.

Here is how I approach it. You have two power lights on the panel, the main power and the STATUS. If the status light doesn't shine, then your screen voltages are missing.

On the power tube board is the large power resistor R86, and I should have B+ on both ends. 480 and 475 on the print. Ballpark is close enough.

But your readings don't make sense. All those voltages come from a string of resistors, high to low. How can you possible have 500v on 28 and 29 when the upstream nodes are either missing or super low? I am led to suspect you were reading the pins counting from the wrong end. Then it makes sense. The two 500v readings would be the plate and screen nodes 25 and 26, then the rest would be low because R99 was open of disconnected.

It can sometimes be difficult to make good contact in those connectors, so a meter might be fooling you, but I don't think it would be so consistent if that were the case.

[sweatyk]

Thanks for your help Enzo. As far as the schematic, layout, and chassis design I would love to put my foot in the backside of the persons at PV that built this. If you have never seen inside these combos you would surely shake your head.

You said, “Here is how I approach it. You have two power lights on the panel, the main power and the STATUS. If the status light doesn't shine, then your screen voltages are missing.”

Are you referring to the 2 Led indicators for the power and standby switches? If so then yes they both light up when the switch is flipped.

“On the power tube board is the large power resistor R86, and I should have B+ on both ends. 480 and 475 on the print. Ballpark is close enough.”

The way the power tube board is mounted I cannot access that resistor or any other part on it. It’s tucked under the main board and the sockets are riveted in. If there is another way to get that voltage reading I’m all ears.

“But your readings don't make sense. All those voltages come from a string of resistors, high to low. How can you possible have 500v on 28 and 29 when the upstream nodes are either missing or super low? I am led to suspect you were reading the pins counting from the wrong end. Then it makes sense. The two 500v readings would be the plate and screen nodes 25 and 26, then the rest would be low because R99 was open of disconnected.”

Enzo I was careful to make sure that I measured the pins in the correct order. I went over it 3 times to be sure. However I will do it again to verify sometime in the next couple of days. I also checked R99 and it was spot on. I will report back what I discover. Thanks again for your assistance.

[Enzo]

Do you at least understand my confusion then? If you have zero or 20v at the starting end of the B+, how could the downstream end have the 500v?

So you measured R99? Can you take voltage readings on each end when powered? R98, 99, 100 appear to be on the control board over near the preamp tubes, and might be accessible peeking out from under the panel.

R96 may be buried, but if both power lights are on, it is OK.

If you pull a preamp tube, the heaters will go out on another tube as well, however the empty socket is a fine place to probe for voltages. Pins 1 and 6 ought to have B+ on them.

[sweatyk]

I managed to spare a few minutes to check these. I will have to get back on the B+ on the tube sockets later. Wanted to post the voltage reading on these.

R98 = 458 / 495 V
R99 = 326 / 457 V
R100 = 305 / 324 V

[g1]

I think you should ignore those J100 series jumpers. They are not shown on the schematic and we don't really know what they correspond to.
You have approx. correct voltages for points on the schematic shown as J24 thru J29. (HV supply rails)
How about J21 & J22, on either side of standby switch?