Eden wt 800 no sound 'R amp/out low'

[nevetslab]

D3 is not shorted measuring with the DMM nor is C11. I put a in a new C11 since I have one. But I don’t have the zener. Do you recommend getting one anyway?
FWIW R26 has .25v
And R28 has .53v

Well, since the two voltages you measured across R24 and R25 showed a difference close to the zener voltage, then measure what the voltage IS at D3/C11. Should be the same (apart from voltage polarity) as that of D5/C10. If you're NOT getting around -6.8VDC at D3/C11, then I would replace the zener. As you don't have that zener (6.8V/1W), can you cobble one from what you do have temporarily? You can also compare readings between this power amp module and the one that IS working for comparison at any of the circuit nodes.

With 0.25V across R26, there's 2.5mA flowing thru Q10 driver, while with 0.53V across R28, there's 5.3mA flowing thru Q11 driver (twice as much).

BTW, after you replaced Q3, Q4, Q5, Q6 & Q8, are you still finding Resistors R9 & R10, along with Q4 still running as hot as before? Any change when you replaced Q8?

In re-reading your earlier post this past Thursday at 5:08AM, I'd try adjusting the DC Offset Trim to see if you can get the voltage across R19/R22 the same (and check what the DC Voltage is on the output buss, as that's what the trim is for). You had 36mA running thru Q8 and 12mA thru Q7.

[pontiacpete]

I finally realized one of the problems I was having, D1 on this board is D2 on the schematic. D2 on the board is D50 on the schematic. I think the problem is with D2. On the cathode of D3 there's -6.8v. That's good right? And there's no voltage on the anode of the D50. On the cathode of D50 which is the buss, there's -1.2v.
I need to order those zeners. The only 6.8v zeners I have are 1/2w, 1n5235.

Oh, the other board, it's not making sound. Post #12 I make a quick mention of the other low point of this endeavor.

I did replace Q8. Also on this board they used a KSE340 and a 350, different from the schematic. I put in a 2n3440 for Q8.

R9, R10 and Q4 are not running hot any longer.
Q16 is little hotter than all the other output transistors.

Thanks for the help!


BTW the 1n4734 is a 5.6v zener. Still don't have it.

[nevetslab]

I finally realized one of the problems I was having, D1 on this board is D2 on the schematic. D2 on the board is D50 on the schematic. I think the problem is with D2. On the cathode of D3 there's -6.8v. That's good right? And there's no voltage on the anode of the D50. On the cathode of D50 which is the buss, there's -1.2v.
I need to order those zeners. The only 6.8v zeners I have are 1/2w, 1n5235.

Oh, the other board, it's not making sound. Post #12 I make a quick mention of the other low point of this endeavor.

I did replace Q8. Also on this board they used a KSE340 and a 350, different from the schematic. I put in a 2n3440 for Q8.

R9, R10 and Q4 are not running hot any longer.
Q16 is little hotter than all the other output transistors.

Thanks for the help!


BTW the 1n4734 is a 5.6v zener. Still don't have it.

My apologies on the zener value. I was going by memory and didn't look it up to confirm. And my mistake calling the upper zener D4, when it IS labeled D50 on my schematic as well. I may have a different schematic where it was labeled D4, but haven't gone back to look.

With Q16 running hotter than the others, do you measure a different voltage drop across its' emitter resistor R33?

If you're seeing -6.8V on the cathode of D3, then you have a DC offset of -6.8V on the amplifier, which is NOT a good sign. We have to find the cause of that. Seeing -1.2V on the cathode of D50 tells us that zener IS ok, it being a 5.6V zener. What do you see on the Anode of D3? If the zener is ok, then it would be -12.4V or close to that.

The use of MJE 340 & MJE350 (or KSExxx) is a suitable replacement for the TO-5 parts, which is what the 2N5415 and 2N3440 parts are.

I must have missed the statement that your other module ALSO wasn't passing signal. I thought you had a working module on the other channel. RATS. The upside is you'll learn more about the circuits and the amplifier when the dust has settled, and the amp works again. Not encouraging at the immediate moment, stuck within the problem(s), but take heart. Logic will prevail, and when restored, it will work as it should.

[pontiacpete]

Geez.... I'm making a mess of this thread AND amp, I made yet another mistake. In my previous post I got anode and cathode of the zener backwards, ugh.
Here is the correct information. D3 has -1.2v on the cathode and -6.6v on the anode. D50 has -1.2v on the anode and -.3v on the cathode.
(BTW Post 26 at 5.08am I call R8 and 11, Q8 and 11, it would be nice if I could correct that)

Q16 - I was using one of those the fluke IR thermometers. The heat sink was getting warm after doing the probing. The only point on the sink that seems to be getting warmer than others is at the body Q16 which was showing 130deg while the others were all at about 86deg. I don't know how accurate this is, just thought I'd mention it.

Anyway thanks for sticking with this, that is if you haven't bailed yet!

[nevetslab]

Geez.... I'm making a mess of this thread AND amp, I made yet another mistake. In my previous post I got anode and cathode of the zener backwards, ugh.
Here is the correct information. D3 has -1.2v on the cathode and -6.6v on the anode. D50 has -1.2v on the anode and -.3v on the cathode.
(BTW Post 26 at 5.08am I call R8 and 11, Q8 and 11, it would be nice if I could correct that)

Q16 - I was using one of those the fluke IR thermometers. The heat sink was getting warm after doing the probing. The only point on the sink that seems to be getting warmer than others is at the body Q16 which was showing 130deg while the others were all at about 86deg. I don't know how accurate this is, just thought I'd mention it.

Anyway thanks for sticking with this, that is if you haven't bailed yet!

D50 is bad, from the readings you're reporting, while D3 is good. If you have any low voltage 1W zeners, and 1N4002 or higher, you could cobble a zener close to 5.6V for temporary to replace D50 and see what the results are. Clip them in with short test leads would be adequate, just making sure it's in-circuit and doesn't come undone during testing. Such as a 3.3V zener, in series with four 1N4001's (or 4002, 4003, etc). Just remember to get the polarity correct on all the diodes relative to the lower voltage zener. For that matter, nine 1N4001 or greater diodes in series would work as a 5.6V zener substitute.

The heat sink under normal idle current on working modules won't get hot to the touch. It may increase 5 deg C over the course of half an hour. If it's getting noticeably warm, then one or more of the power xstrs are conducting. You'd see that current as voltage drop across the 0.47 ohm/5W emitter resistors.

The amp WILL work with only one pair of output xstrs installed (Q12/Q13, assuming the layout and the schematic are correct, as far as trouble-shooting the amp's circuit stages.

You also have the ability to turn the bias OFF, just to see what impact that has on the Driver Stage, Voltage Gain stage and Input stage. Turning Q9 on hard will reduce the voltage at the bases of driver xstrs Q10 & Q11, turning off the output stage. That potential between the bases at nominal bias (7mV between Q12 & Q13 emitters) would be in the range of 1.9V to 2.1V.

I'll hang in there with you, as it's also a quest for me to see this thru. Not having access to my shop leaves tech work to be done this way, and is always enjoyable so hang in there.

[pontiacpete]

I found three 5.6v zeners 1n4734s. (Although I really like the ideas you have for cobbling up a Zener using 1n4001/2) Put one in for D2 but the problem was still there so I changed the parallel cap and now there’s 5.6 on the cathode is D2 but this brought the voltage down to -5.2v on D3.
And the large heat sink isn’t getting warm.
But there’s still no sound. I suppose we’re back to where we started. I should reread the thread.

[nevetslab]

I found three 5.6v zeners 1n4734s. (Although I really like the ideas you have for cobbling up a Zener using 1n4001/2) Put one in for D2 but the problem was still there so I changed the parallel cap and now there’s 5.6 on the cathode is D2 but this brought the voltage down to -5.2v on D3.
And the large heat sink isn’t getting warm.
But there’s still no sound. I suppose we’re back to where we started. I should reread the thread.

I assume you meant D50 and not D2 (which is feeding the gates of Q1 & Q2). I'm not sure why the zener voltage of D3 is now lower than it was. You might want to change it as well, as you found three of the 1N4734 zeners. Still no sound, though.

Now, I'd go back thru the stages to see what voltages you have at the HV Power Supplies, collector resistors R8 (Q3 Collector) and R11 (Q4 Collector), R19 (emitter of Q7), R22 (emitter of Q8), Base of Q10 & Q11, as well as emitters of Q10 & Q11.and output buss voltage. I gave you the nominal voltages a few posts ago. If your voltages are close to that, we could set the bias as well as the DC Offset to zero volts. Good to hear you're not getting a hot heat sink, indicating you're not pulling a lot of current thru the output stage.

I've lost signal at the output thermal switch on one of these WT800's before.....it was a bad crimp on the output thermal switch, which is in series with the output connectors. Though we need to see signal at the drivers, which so far, we haven't.

Initially, I believe you had signal appearing at both the collectors of Q3 & Q4, but nowhere past that.

[pontiacpete]

Oh yes I meant D50!
Here are the voltages
Collector Q3 is 78.5v. And Q4 is -81v
Emitter Q7 is 83v and Q8 is -81.5v
Base Q10 and Q11 is 0v.
The buss is about a -1v
D3 I changed but still has -5.1v. And D50 has 5.5v

There some sort of connection issue,come to find out. When I press on the board the voltages drop on D3 and 50 and probably throughout and the heat sink gets hot. I havE to find the source of this.

[pontiacpete]

This is getting weird. I just went in and touched up the solder joints on the output and driver transistors and now it’s worse. No voltage on D 3 and 50 and a hot heat sink. Ugh!

Edit: I wonder if I should just shotgun the rest of the transistors on this module or just give up. Now I'm getting -15v on D50. There might be a connection issue between the top of the board and the bottom, being a 2 sided PCB.

[pontiacpete]

Pulled the heat sink off the board, unscrewed all the outputs and drivers and sucked old lead free(or whatever they used) and put in new solder. Replaced Q9,10 and 11 and D3(again). And I'm still getting -15v on D3.

Perhaps I should have chosen to give up.

[nevetslab]

Pulled the heat sink off the board, unscrewed all the outputs and drivers and sucked old lead free(or whatever they used) and put in new solder. Replaced Q9,10 and 11 and D3(again). And I'm still getting -15v on D3.

Perhaps I should have chosen to give up.

I feel your frustration. I don't believe we've seen -15V on D3 before, though that's no doubt the zener voltage plus DC offset. But, you've kind of revealed where the problem isn't.....the output stage. At this point, you could remove Q10 & Q11, leaving the rest of the circuits in place. Place a jumper from the emitter resistors of Q10 & Q11, so the bases of the output xstrs are shorted together, which will insure they're turned off. Place a jumper between the collectors of Q7 & Q8, and tie that to the output buss. This makes the front end Voltage gain stage into a high voltage op amp. Then, see what the voltages are as I had requested before (collectors of the double-diff amp front end, voltages at the emitters of Q7 & Q8, along with the supply voltages, so we can see what the currents are thru the front end and voltage gain stage. It could be as simple as a resistor that's open causing all this.

Or, another way would be to remove Q7 & Q8, leaving Q10 & Q11 in circuit. Jumper the bases of Q10 & Q11 together, so the output stage is turned off. Then, see what the voltages are at the two zeners that tie to the collectors of Q10 & Q11 are. The output buss SHOULD remain at 0V. If not, then there still may be a problem in the network comprised of R24, D50, C10, D4, D3, D5, C11, R25 & R27/R27A. Also verify feedback resistor R18, and shunt resistor R17 and it's LF rolloff cap C6 are ok.

But, if you've had enough and want to give up, I do understand. Is this your amp, or a client's amp?

[nevetslab]

Oh yes I meant D50!
Here are the voltages
Collector Q3 is 78.5v. And Q4 is -81v
Emitter Q7 is 83v and Q8 is -81.5v
Base Q10 and Q11 is 0v.
The buss is about a -1v
D3 I changed but still has -5.1v. And D50 has 5.5v

There some sort of connection issue,come to find out. When I press on the board the voltages drop on D3 and 50 and probably throughout and the heat sink gets hot. I havE to find the source of this.

OH.....I missed this thread. Sorry. I didn't see what the supply voltages are. We still have the DC imbalance on the front end circuit. Without the supply voltages, I can't calculate the branch currents thru the front end and voltage gain stage circuits.

You're key is pressing on the PCB, and finding the voltages change, AND the heat sink gets hot. I've had solder joint problems on the Eden Power Amp modules, and have had to re-connect circuits back together with buss wires and discrete wires to restore order. I've also had problems with the connections at the 6-pin header, as well as having lost connections at the driver xstrs, outputs and bias xstrs, so indeed you do have this sort of thing occurring, and, at this point from all we've seen, is LIKELY to be the CAUSE of all this mess! I go hunting with bright light and magnification (as seen in my Avatar.....surgical head light and 2.5X loupes.....magnification and bright light to reveal the faults, along with DMM in Ohmmeter mode to confirm when nothing else is obvious.

[pontiacpete]

I wasn’t able to see your last post because the site was down, so I went ahead and pulled Q7 and 8. Both of the zeners are back to 5.6v and -5.2v. The buss has .12v.
This not my amp. It belongs to one of the shops I do work for. It’s one of a number amps they have I suppose, and they thought it might be easily fixed. I’ve had it here a long time waiting for me to get the gumption to give it a try. And maybe I might learn a thing of two. So if it doesn’t get fixed no problem, there’s no one waiting to do gigs with. Heck there aren’t any gigs around here anyway.

So yesterday I detached the heat sink from the PCB and checked and re- solders all the output transistors and drivers and cleaned things up. Re-tensioned the molex connector. Now when I just turned it on the voltage on D50 comes up to 5.6v while D3 comes up slowly and was fluctuating between 4.6amd 5v until it finally settled at 5.3v. That could my clip lead or some other reason. I don’t dett

[nevetslab]

I wasn’t able to see your last post because the site was down, so I went ahead and pulled Q7 and 8. Both of the zeners are back to 5.6v and -5.2v. The buss has .12v.
This not my amp. It belongs to one of the shops I do work for. It’s one of a number amps they have I suppose, and they thought it might be easily fixed. I’ve had it here a long time waiting for me to get the gumption to give it a try. And maybe I might learn a thing of two. So if it doesn’t get fixed no problem, there’s no one waiting to do gigs with. Heck there aren’t any gigs around here anyway.

So yesterday I detached the heat sink from the PCB and checked and re- solders all the output transistors and drivers and cleaned things up. Re-tensioned the molex connector. Now when I just turned it on the voltage on D50 comes up to 5.6v while D3 comes up slowly and was fluctuating between 4.6amd 5v until it finally settled at 5.3v. That could my clip lead or some other reason. I don’t dett

Could be lead corrosion on R25 6.8k/2W which feeds D3 & Q11. Maybe C11 is defective. I think you said you had replaced C10, though I'd have to dig back thru the dialog on the earlier posts. I've also had to remove emitter resistors and the vertically mounted 5W & 2W resistors to address the lead corrosion before. At least one time that was a problem, though I'd have to dig thru all my Eden WT800 files to see.

I could compile my Eden WT800 Service Notes and send those to you. I've done that sort of 'maintenance journal' on a number of other products that I do a lot of work on, which have had a wide range of common problems. I'll get back to you on that. I do have time these days, not being able to spend time in my shop, since CenterStaging, LLC is shut down until it's safe for large gatherings of all of us without having major outbreaks of the virus again. My shop is at their facility in Burbank, CA.

At any rate, it's encouraging to see what you've read with the front end detached from the power amp's current gain stages. You're getting closer now.

[nevetslab]

Eden WT800 Service Notes 2013-2019

I went thru my files and extracted all of the Service Notes on the Eden WT800 I had from Aug 2013 thru Nov 2019. Both in MS Word and PDF. I haven't reviewed all of them, just did a quick compiling from tracking them down thru invoicing dates, then looking up the service notes from those dates. There's no doubt a lot of typo's in the 2016-2018 period, prior to my cataract surgery. In that period, seemed like my fingers were dyslexic. Most were from either CenterStaging, LLC's rental inventory or AuntieM Creative Consultant's rental inventory, out here in the Los Angeles Area.

Eden WT800 Service Notes.doc

Eden WT800 Service Notes.pdf