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Author Topic: Peavy Rage 158 no sound after 1-5 mins  (Read 642 times)

substatica

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Peavy Rage 158 no sound after 1-5 mins
« 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?

Enzo

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Re: Peavy Rage 158 no sound after 1-5 mins
« Reply #1 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.

substatica

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Re: Peavy Rage 158 no sound after 1-5 mins
« Reply #2 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.
« Last Edit: June 14, 2019, 07:29:12 PM by substatica »

substatica

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Re: Peavy Rage 158 no sound after 1-5 mins
« Reply #3 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
« Last Edit: June 14, 2019, 07:27:24 PM by substatica »

substatica

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Re: Peavy Rage 158 no sound after 1-5 mins
« Reply #4 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.

Enzo

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Re: Peavy Rage 158 no sound after 1-5 mins
« Reply #5 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?


substatica

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Re: Peavy Rage 158 no sound after 1-5 mins
« Reply #6 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.


substatica

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Re: Peavy Rage 158 no sound after 1-5 mins
« Reply #7 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.

substatica

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Re: Peavy Rage 158 no sound after 1-5 mins
« Reply #8 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 ;)

substatica

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Re: Peavy Rage 158 no sound after 1-5 mins
« Reply #9 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.
« Last Edit: June 15, 2019, 02:43:23 PM by substatica »

substatica

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Re: Peavy Rage 158 no sound after 1-5 mins
« Reply #10 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.

Enzo

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Re: Peavy Rage 158 no sound after 1-5 mins
« Reply #11 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.

substatica

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Re: Peavy Rage 158 no sound after 1-5 mins
« Reply #12 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?

substatica

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Re: Peavy Rage 158 no sound after 1-5 mins
« Reply #13 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.

galaxiex

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Re: Peavy Rage 158 no sound after 1-5 mins
« Reply #14 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

If using a split supply, pin 3 and the heat sink tab MUST NOT be grounded.
« Last Edit: June 16, 2019, 11:48:59 AM by galaxiex »
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