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Author Topic: Peavy Rage 158 no sound after 1-5 mins (SOLVED)  (Read 2650 times)

phatt

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Re: Peavy Rage 158 no sound after 1-5 mins
« Reply #30 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.

substatica

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Re: Peavy Rage 158 no sound after 1-5 mins
« Reply #31 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.

g1

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Re: Peavy Rage 158 no sound after 1-5 mins
« Reply #32 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.

substatica

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Re: Peavy Rage 158 no sound after 1-5 mins
« Reply #33 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.

substatica

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Re: Peavy Rage 158 no sound after 1-5 mins
« Reply #34 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.

« Last Edit: August 06, 2019, 10:27:52 PM by substatica »

phatt

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Re: Peavy Rage 158 no sound after 1-5 mins
« Reply #35 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.

substatica

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Re: Peavy Rage 158 no sound after 1-5 mins
« Reply #36 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.
« Last Edit: August 07, 2019, 10:22:18 AM by substatica »

substatica

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Re: Peavy Rage 158 no sound after 1-5 mins
« Reply #37 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.
« Last Edit: August 07, 2019, 07:05:40 PM by substatica »

phatt

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Re: Peavy Rage 158 no sound after 1-5 mins
« Reply #38 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.

phatt

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Re: Peavy Rage 158 no sound after 1-5 mins
« Reply #39 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.

substatica

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Re: Peavy Rage 158 no sound after 1-5 mins
« Reply #40 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.
« Last Edit: August 08, 2019, 05:33:59 PM by substatica »

phatt

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Re: Peavy Rage 158 no sound after 1-5 mins (SOLVED)
« Reply #41 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.

substatica

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Re: Peavy Rage 158 no sound after 1-5 mins (SOLVED)
« Reply #42 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.

g1

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Re: Peavy Rage 158 no sound after 1-5 mins (SOLVED)
« Reply #43 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?

substatica

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Re: Peavy Rage 158 no sound after 1-5 mins (SOLVED)
« Reply #44 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.
« Last Edit: August 09, 2019, 02:30:51 PM by substatica »

 

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