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Solid State Amplifiers => Amplifier Discussion => Topic started by: substatica on June 14, 2019, 12:35:51 PM

Title: Peavy Rage 158 no sound after 1-5 mins (SOLVED)
Post by: substatica on June 14, 2019, 12:35:51 PM
Picked-up a Peavy Rage 158 that wasn't working right for another fellow. Found a cold/bad solder joint which fixed a board wiggling cut-out issue. Now everything works fine for a couple of minutes, then no sound. Cycling the amp power brings it back, just off long enough to hear the "turning off pop" then back on, so that tells me maybe not a heat issue as it wouldn't have cooled that much, but is perhaps after a cap discharge? Any ideas of where to start?
Title: Re: Peavy Rage 158 no sound after 1-5 mins
Post by: Enzo on June 14, 2019, 02:53:25 PM
Next time it kills the sound, leave it running, ball up your fist, and whack the top of the amp.  Does the amp come back on, even for a moment?  Does the amp react to your whack in ANY way, like a noise?

When it dies, listen CLOSELY to the speaker, is there any background hum or hiss?  Turn up the controls to hear that better potentially.   If there is any such background, to the volume and tone controls affect it at all?

Get the schematic from customer service at Peavey, and then see if your power supplies are remaining up or if they are going out.

With it running and signal applied, poke each part on the board with a wooden chopstick or similar.
Title: Re: Peavy Rage 158 no sound after 1-5 mins
Post by: substatica on June 14, 2019, 06:44:41 PM
I whacked the cab a bunch after it dropped, no effect what-so-ever, even lifted 1/2" and dropped it, that sort of thing, nothing. Power cycle and it's back. Got it open again and I'll start taking some readings.

Update: Removed incorrect schematic.
Title: Re: Peavy Rage 158 no sound after 1-5 mins
Post by: substatica on June 14, 2019, 07:20:54 PM
Q: Next time it kills the sound, leave it running, ball up your fist, and whack the top of the amp.  Does the amp come back on, even for a moment?
A: No.

Q: Does the amp react to your whack in ANY way, like a noise?
A: No.

Q: When it dies, listen CLOSELY to the speaker, is there any background hum or hiss? 
A: Yes.

Q: Turn up the controls to hear that better potentially.   If there is any such background, to the volume and tone controls affect it at all?
A: Low hum, not affected by volume or tone, buzzes louder if I short the signal cable with my thumb.

Q: Get the schematic from customer service at Peavey, and then see if your power supplies are remaining up or if they are going out.
A: 120VA into the transformer, 25VA out  in the no-signal state.

Q: With it running and signal applied, poke each part on the board with a wooden chopstick or similar.
A: No effect.

I tested the diodes, they all read good except for the two 1N4003's by the power transistor, they short both ways -- maybe that's expected? It also seems if I leave it on in the no-signal state for 5 minutes or so the power cycle no longer fixes the issue, I'll have to wait and see if it works again after being off for a while. That brings me back to heat, but nothing on the board seems overly hot (hit it with infrared thermometer).

Also, still trying to determine if that's the correct schematic. It's a Peavy Rage 158 w/ Transtube, but the component markings aren't all matching up. The initial sold solder I fixed was on an R49 which I can't seem to locate.

The amp is the same as the one pictured on this thread,

https://www.diystompboxes.com/smfforum/index.php?topic=97068.0
Title: Re: Peavy Rage 158 no sound after 1-5 mins
Post by: substatica on June 14, 2019, 08:25:49 PM
Here's the amp. The initial problem I fixed was the top, left-most solder joint on R49 had cracked out. Probably due to the board mounted jacks and minimal board support.
Title: Re: Peavy Rage 158 no sound after 1-5 mins
Post by: Enzo on June 15, 2019, 04:25:47 AM
The PV Rage and Blazer are the same amp.  The Blazer just includes a reverb, the Rage does not.  The "missing" parts on your board are the reverb circuits not installed.

What exactly does the amp call itself on the serial number plate?  Rage 158 TT?  Are there any other numbers there like '92.


Does this drawing set match your board better?

Title: Re: Peavy Rage 158 no sound after 1-5 mins
Post by: substatica on June 15, 2019, 09:03:54 AM
Q: What exactly does the amp call itself on the serial number plate?  Rage 158 TT?  Are there any other numbers there like '92.
A: TRANSTUBE RAGE

Q: Does this drawing set match your board better?
A: Yes, I think that's it. Thanks.

Title: Re: Peavy Rage 158 no sound after 1-5 mins
Post by: substatica on June 15, 2019, 11:25:51 AM
I can't get any signal out of it now, seems like I left it on long enough for something to fry for good. All of the voltages checked against the schematic seem within reason 3.2 VDC where it says 3, 26.8 VDC where it says 25, 30.7 VDC where it says 27. Nothing too out of whack.

One odd thing is when I touch D7 it reads 13.8 VDC, but I get a big pop and radio starts coming through.
Title: Re: Peavy Rage 158 no sound after 1-5 mins
Post by: substatica on June 15, 2019, 01:32:35 PM
Took the board off, pulled the solder off R49 again, cleans the area (some brown residue), soldered it back again, took off C31 and it read fine. Re-flowed some questionable looking pads and it's working again. Have to try it for an extended period once my  8-month-old is up from his nap ;)
Title: Re: Peavy Rage 158 no sound after 1-5 mins
Post by: substatica on June 15, 2019, 02:24:33 PM
It seems the power transistor is grounding through the heat sink to the chassis and that causes the signal to cut out. So by taking the board off everything worked, putting it back the transistor grounds and the signal cuts out.

I guess previously there was enough heat sink compound to prevent the short, and when it got hot enough it conducted, when I replaced the board the first time I must have put it on more secure and therefore made the short permanent (until I took the board off again).

It seems, by the layout that it's suppose to ground here anyway. Could they really have been depending on the heat sink compound to prevent this?

Unless the TDA2040 has an internal short.
Title: Re: Peavy Rage 158 no sound after 1-5 mins
Post by: substatica on June 15, 2019, 05:39:18 PM
Yeah it seems like if I ground the board to the chassis anywhere then I lose signal.
Title: Re: Peavy Rage 158 no sound after 1-5 mins
Post by: Enzo on June 15, 2019, 08:39:53 PM
The thermal compound grease is NOT an insulator.  There should be a mica or silicone wafer between the power amp IC and the heat sink.   You are shorting the power supply to ground.
Title: Re: Peavy Rage 158 no sound after 1-5 mins
Post by: substatica on June 16, 2019, 09:07:49 AM
The thermal compound grease is NOT an insulator.  There should be a mica or silicone wafer between the power amp IC and the heat sink.   You are shorting the power supply to ground.

There is/was no wafer -- should I add one? Is that the solution here to prevent the board from grounding on the chassis? Or would this be happening due to a component failure?
Title: Re: Peavy Rage 158 no sound after 1-5 mins
Post by: substatica on June 16, 2019, 09:51:33 AM
None of the photos of this amp that I've found (three or four examples) have any wafer under the IC, just some thermal compound. So something else must have gone wrong.
Title: Re: Peavy Rage 158 no sound after 1-5 mins
Post by: galaxiex on June 16, 2019, 11:47:17 AM
Pin 3 of the TDA2040 is connected to the heat sink tab.

If the supply is single ended, pin 3 can be grounded, according to the data sheet.

https://www.st.com/resource/en/datasheet/cd00000130.pdf (https://www.st.com/resource/en/datasheet/cd00000130.pdf)

If using a split supply, pin 3 and the heat sink tab MUST NOT be grounded.
Title: Re: Peavy Rage 158 no sound after 1-5 mins
Post by: g1 on June 16, 2019, 04:29:48 PM
Schematic shows pin3 connected to ground, so no insulation needed for the IC.
Check D10 in circuit with your meter.  Check for any solder bridges at the IC pins.
Title: Re: Peavy Rage 158 no sound after 1-5 mins
Post by: substatica on June 17, 2019, 09:06:00 AM
Schematic shows pin3 connected to ground, so no insulation needed for the IC.
Check D10 in circuit with your meter.  Check for any solder bridges at the IC pins.

D10 and D9 I get a beep both polarities with the diode test on my meter. I pulled them out before and they tested fine out of circuit.
Title: Re: Peavy Rage 158 no sound after 1-5 mins
Post by: g1 on June 17, 2019, 12:09:52 PM
Check with meter set to ohms, lowest range.  Across D10, with it in circuit.
Title: Re: Peavy Rage 158 no sound after 1-5 mins
Post by: substatica on June 17, 2019, 01:09:18 PM
Check with meter set to ohms, lowest range.  Across D10, with it in circuit.

Seems to be all over the place. Either climbing to around 250k Ohms one polarity, other polarity drops from from 1m Ohm. But I also get all sorts of other readings across it.
Title: Re: Peavy Rage 158 no sound after 1-5 mins
Post by: g1 on June 19, 2019, 04:24:53 PM
Can you check same with the board fully mounted?
Title: Re: Peavy Rage 158 no sound after 1-5 mins
Post by: substatica on June 19, 2019, 10:40:09 PM
Can you check same with the board fully mounted?

Basically the same, once side climbs up to 260k, the other climbs down from 1.2m until about 300k then drops to 0 and starts climbing up.
Title: Re: Peavy Rage 158 no sound after 1-5 mins
Post by: g1 on June 20, 2019, 12:10:20 AM
How about checking resistance from heatsink to each of the IC pins.  The only one that should be low resistance is pin 3.
Title: Re: Peavy Rage 158 no sound after 1-5 mins
Post by: substatica on June 20, 2019, 07:34:40 AM
How about checking resistance from heatsink to each of the IC pins.  The only one that should be low resistance is pin 3.

Pin 3 is a dead short, as expected. The other pins are 250k or over 1m.
Title: Re: Peavy Rage 158 no sound after 1-5 mins
Post by: g1 on June 20, 2019, 01:46:19 PM
How about resistance of R44 to ground?  (try both sides)
Title: Re: Peavy Rage 158 no sound after 1-5 mins
Post by: substatica on June 20, 2019, 02:27:34 PM
How about resistance of R44 to ground?  (try both sides)

2.5m on both sides. Resistor reads proper at 4.7r across.
Title: Re: Peavy Rage 158 no sound after 1-5 mins
Post by: psafloyd on July 04, 2019, 02:10:56 PM
There are at least two editions of the 158 Rage. The later/latest one had a switch to switch between modern and vintage voicings. If your one has this and the schematic doesn't, it could be more than the switch got altered.
   

Q: Next time it kills the sound, leave it running, ball up your fist, and whack the top of the amp.  Does the amp come back on, even for a moment?
A: No.

Q: Does the amp react to your whack in ANY way, like a noise?
A: No.

Q: When it dies, listen CLOSELY to the speaker, is there any background hum or hiss? 
A: Yes.

Q: Turn up the controls to hear that better potentially.   If there is any such background, to the volume and tone controls affect it at all?
A: Low hum, not affected by volume or tone, buzzes louder if I short the signal cable with my thumb.

Q: Get the schematic from customer service at Peavey, and then see if your power supplies are remaining up or if they are going out.
A: 120VA into the transformer, 25VA out  in the no-signal state.

Q: With it running and signal applied, poke each part on the board with a wooden chopstick or similar.
A: No effect.

I tested the diodes, they all read good except for the two 1N4003's by the power transistor, they short both ways -- maybe that's expected? It also seems if I leave it on in the no-signal state for 5 minutes or so the power cycle no longer fixes the issue, I'll have to wait and see if it works again after being off for a while. That brings me back to heat, but nothing on the board seems overly hot (hit it with infrared thermometer).

Also, still trying to determine if that's the correct schematic. It's a Peavy Rage 158 w/ Transtube, but the component markings aren't all matching up. The initial sold solder I fixed was on an R49 which I can't seem to locate.

The amp is the same as the one pictured on this thread,

https://www.diystompboxes.com/smfforum/index.php?topic=97068.0
Title: Re: Peavy Rage 158 no sound after 1-5 mins
Post by: substatica on July 04, 2019, 04:27:24 PM
There are at least two editions of the 158 Rage. The later/latest one had a switch to switch between modern and vintage voicings. If your one has this and the schematic doesn't, it could be more than the switch got altered.

Mine does have this switch, but the schematic seems pretty bang-on, I'll have to look closely for differences.
Title: Re: Peavy Rage 158 no sound after 1-5 mins
Post by: substatica on August 04, 2019, 12:55:17 PM
I replaced C26 which is listed as 100nf, but the actual component was 200nf.

The board can ground to the chassis and everything works -- however if the ground of the input jack is connected to the chassis (as it is when assembled as a plate on the jack tightens against the chassis) the signal drops out.

Thoughts? Summarizes as the signal lost when input ground connects to chassis.
Title: Re: Peavy Rage 158 no sound after 1-5 mins
Post by: phatt on August 05, 2019, 06:22:49 AM
Best I can make out is that you have 2 Grounds/Commons.
AGND1 & AGND.
AGND1 is likely Com for chassis as well as power amp but after that the ground is lifted by R63 (47R).
So AGND is separated from ANGD1 by R63.
I can only assume that grounding the input socket upsets the bias of the whole preamp. Better minds may know more?

The schematic shows the input com tag is actually grounded to Chassis so it makes no sense as drawn. xP

The drawing also shows the input socket (J1) is a switching socket but your picture shows a non switching socket.
I can only assume it has been replaced at some point,, possibly you need a switching socket.
sorry i can't be more help.
Phil.
Title: Re: Peavy Rage 158 no sound after 1-5 mins
Post by: substatica on August 05, 2019, 08:17:51 AM
The picture is a switching socket, inserting the 1/4" plug lifts the contacts opening the switches.

Upsetting the bias sounds like it may be the case because the max volume seems to fluctuate if the ground contact is intermittent.
Title: Re: Peavy Rage 158 no sound after 1-5 mins
Post by: phatt on August 06, 2019, 07:35:03 AM
Thanks for the clarification,, well if it works fine then maybe just work out a way to isolate the input socket.

If the socket is ALL plastic then it seems odd that it grounds to chassis. :loco
But have a close look at the face of the socket,, where it contacts the chassis.

There are some plastic sockets that have a metal pin which grounds to chassis when you mount them.
The Schemo shows an extra terminal which gives a clue that it might be that type of socket.
Phil.
Title: Re: Peavy Rage 158 no sound after 1-5 mins
Post by: substatica on August 06, 2019, 08:24:40 AM
The grounding is intentional, there's a conductive plate that is soldered to the jack's ground lugs and folds in front of the jack to ground with the chassis. Both for the instrument input and the CD input. If it didn't seem intentional, yeah, I'd just isolate and close it up, but something's off.
Title: Re: Peavy Rage 158 no sound after 1-5 mins
Post by: g1 on August 06, 2019, 01:28:39 PM
I'm not sure your test set-up, but it's critical that you do not ground the speaker (-) with any test gear, grounded load, etc.
If you do so you short out R43, which can cause all manner of weirdness.
Title: Re: Peavy Rage 158 no sound after 1-5 mins
Post by: substatica on August 06, 2019, 02:55:22 PM
I'm not sure your test set-up, but it's critical that you do not ground the speaker (-) with any test gear, grounded load, etc.
If you do so you short out R43, which can cause all manner of weirdness.

Hrm, I may have inadvertently reverse the speaker polarity, but I don't believe I've grounded it out, something to check. Also that the speaker leads are short-free too I guess.
Title: Re: Peavy Rage 158 no sound after 1-5 mins
Post by: substatica on August 06, 2019, 07:30:49 PM
Okay, interesting discovery tonight. It's only when both the TDA2040 heat sink (AGND1) and the input jack ground (AGND) connect with the chassis that the signal drops out. So that would seem to short the two grounds together, which I assume are suppose to be isolated?

This would mean that the thermal paste between the TDA2040 and its heat sink was the only thing preventing this from happening previously until it wore away?

AGND1 has a circle around it in the circuit diagram AGND does not (and input jack ground actually says "CHAS", what does that indicate?

Update: Circled Ground No. 5018 Noiseless (clean) earth (ground): To identify a noiseless (clean) earth (ground) terminal, e.g. of a specially designed earthing (grounding) system to avoid causing malfunction of the equipment.

Title: Re: Peavy Rage 158 no sound after 1-5 mins
Post by: phatt on August 07, 2019, 03:40:18 AM
*Chas* would obviously mean Chassis/Case.

I can only assume that input socket is meant to be grounded to Chassis and therefore the Power chip needs to be isolated with a mica washer or silicon pad.

The break between the 2 grounds can also be seen at R49 / C32 of the power supply.
Phil.
Title: Re: Peavy Rage 158 no sound after 1-5 mins
Post by: substatica on August 07, 2019, 07:46:34 AM
*Chas* would obviously mean Chassis/Case.

I can only assume that input socket is meant to be grounded to Chassis and therefore the Power chip needs to be isolated with a mica washer or silicon pad.

The break between the 2 grounds can also be seen at R49 / C32 of the power supply.
Phil.

I worded that wrong, I realized CHAS meant Chassis, by "what does that indicate" I was asking about two grounds in general. It does seem like this is the issue, one I suspected early on, but I found no evidence of a mica washer or silicon pad, perhaps it had been lost/removed before I got this amp -- but I don't see one in any other photos of this amp online, though they're not the clearest shots.

Attached photo of another Rage 158 with TDA2040 in place as I found this one, with only some sort of thermal compound isolating.
Title: Re: Peavy Rage 158 no sound after 1-5 mins
Post by: substatica on August 07, 2019, 07:00:10 PM
Ug, I put a silicon pad between the TDA2040 and the heat sink and another between the heat sink and the chassis and all seemed well.

Until I put it in the cabinet and tightened the strap bolts that go through the chassis, when they're all the way tightened something else must be grounding out as the signal drops.

If I turn it on with the bolts tighten the sound starts very low and then fades out. If I loosen the bolts the signal comes back. The only thing it seems the bolts could do is warp the board slightly -- I didn't see any damage to the board that would suggest a cracked trace or whatnot.

Out she comes.
Title: Re: Peavy Rage 158 no sound after 1-5 mins
Post by: phatt on August 07, 2019, 11:45:35 PM
The best I can make out between the schematic and pcb layout at the bottom of PDF is that the tab of the power chip needs to be grounded to the heat sink but the heat sink should be isolated from Chassis.  So I think you are on the right track.

That pcb pic shows D10 and a wire link connected to a copper pad (right side of U1) which connects to the heat sink when bolted down.

I can only assume the 2 screws should be insulated from the heat sink and the heat sink is then isolated from case via a mica washer.
But the screws would need to pass through a plastic sleeve so as not to make contact with the heat sink.

Maybe parts were lost when someone fiddled with the amp before you got it.
Phil.
Title: Re: Peavy Rage 158 no sound after 1-5 mins
Post by: phatt on August 08, 2019, 01:44:09 AM
AGND1 has a circle around it in the circuit diagram AGND does not (and input jack ground actually says "CHAS", what does that indicate?

Update: Circled Ground No. 5018 Noiseless (clean) earth (ground): To identify a noiseless (clean) earth (ground) terminal, e.g. of a specially designed earthing (grounding) system to avoid causing malfunction of the equipment.

Yes the circle obviously means it's isolated or ground lifted from chassis.
Basic logic suggests that U1 is directly coupled to heat sink (no washer) but the heat sink MUST be isolated from Chassis for that to work.
Phil.
Title: Re: Peavy Rage 158 no sound after 1-5 mins
Post by: substatica on August 08, 2019, 08:09:10 AM
I think I've got it licked. I'm pretty sure there's no missing hardware. They just put non-conductive thermal compound between the TDA2040 and the heat sink and between the heat sink and the chassis. I added silicon pads between them and that seems sorted out.

The last issue (hopefully) was that flexing the chassis at all, which happened when the strap bolts were tight, would cause the signal to cut out. I poked around with a chop stick, poking and flexing the board and C23 seemed to react quite sensitively. C23 showed no visible damage or bad joint, but I pulled it, tested it (tested good) and resoldered it and now I can't seem to trigger the issue. Must have been a cold joint at C23 that wasn't visible (or at Pin 5 of the TDA2040 which is on the same trace).

Currently I'm 3d-printing a couple of pillar-type supports to ease the pressure of the strap bolts on the chassis and then I'll re-assemble and test again before calling this solved.

Update: Reassembled and all seems good. Thanks everyone who contributed.
Title: Re: Peavy Rage 158 no sound after 1-5 mins (SOLVED)
Post by: phatt on August 08, 2019, 10:37:48 PM
 :dbtu:

BTW, Thermal Paste although not conductive does not Isolate.
Never rely on it as an insulator, you need the washer.

Re the pic,,The tab of U1 is still grounded because the screw is not insulated.
But don't try to insulate it as that will break the link with C26 and D10.
Phil.
Title: Re: Peavy Rage 158 no sound after 1-5 mins (SOLVED)
Post by: substatica on August 08, 2019, 11:23:28 PM
:dbtu:

BTW, Thermal Paste although not conductive does not Isolate.
Never rely on it as an insulator, you need the washer.

Re the pic,,The tab of U1 is still grounded because the screw is not insulated.
But don't try to insulate it as that will break the link with C26 and D10.
Phil.

Yeah, I did realize that, however, as best I can tell, this is the original setup of the amp, which is what I was trying to get back to. I don't have it open right now, but the final resistance from the U1 tab to ground was like 700k.

At best, if we consider the paste (or my silicon pads) non-conductive and the parts of the circuit board that the heat sink screws are through are AGND and not AGND1 (I didn't check) then it's the screw through U1 and the screws through the heat sink that are the conductive path and perhaps coated to increase resistance. I emailed Peavey to see what the intention was here.

If someone else stops by with a Rage 158 that is stock they could let us know what the deal is here.
Title: Re: Peavy Rage 158 no sound after 1-5 mins (SOLVED)
Post by: g1 on August 09, 2019, 01:50:34 PM
This is so bizarre to me that I have to make an analogous statement just to show how illogical this is.
Pin3 of TDA2040 is connected to chassis via AGND1.  Now if we insulate the tab of the TDA2040, and run an extra wire from pin3 to chassis, the chip will overheat and shut down.   ???

Has R63 been verified ok with at least one end lifted?
Title: Re: Peavy Rage 158 no sound after 1-5 mins (SOLVED)
Post by: substatica on August 09, 2019, 02:04:02 PM
This is so bizarre to me that I have to make an analogous statement just to show how illogical this is.
Pin3 of TDA2040 is connected to chassis via AGND1.  Now if we insulate the tab of the TDA2040, and run an extra wire from pin3 to chassis, the chip will overheat and shut down.   ???

Has R63 been verified ok with at least one end lifted?

I don't think I lifted R63, but I did check it, if a resistor reads its proper value and doesn't show any damage I generally test them in circuit. I did pull most of the electrolytics, a bunch of the other caps and diodes and everything has tested fine, and showed no signs of damage.
Title: Re: Peavy Rage 158 no sound after 1-5 mins (SOLVED)
Post by: substatica on August 09, 2019, 02:34:34 PM
Pin3 of TDA2040 is connected to chassis via AGND1.  Now if we insulate the tab of the TDA2040, and run an extra wire from pin3 to chassis, the chip will overheat and shut down.   ???

As far as I can tell AGND1 should not ground to chassis. AGND is the chassis ground. It could have been a combination of the missing thermal compound (which I cleaned off when I disassembled) which dropped the resistance between AGND and AGND1 and a cold joint destabilizing the circuit in another way.
Title: Re: Peavy Rage 158 no sound after 1-5 mins (SOLVED)
Post by: Enzo on August 09, 2019, 06:01:51 PM
All the grounds are grounds, they are just not all wired in common.  This is to prevent instability or ground loops.  The power supply might have a separate ground from the preamp, but the input jack connects both together and to chassis.  That sort of thing.  SOme complex amps like 5150 can have five or six ground circuits.  They all join, usually at a panel jack.  R63 links them here.