It never fails to amaze me what people or "techs" do to equipment!!!

jbeckva

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Yep, will do Dave.

In the meantime (along the lines of this thread here.. hehe)... Anyone see that 400 on ebay with the fuseholders... sticking out of the FRONT??? Now that's ummm.. hmmmm... "interesting", I guess.:cyclopsani:
 
Gepetto

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jbeckva said:
Yep, will do Dave.

In the meantime (along the lines of this thread here.. hehe)... Anyone see that 400 on ebay with the fuseholders... sticking out of the FRONT??? Now that's ummm.. hmmmm... "interesting", I guess.:cyclopsani:
Click to expand...
I actually have seen many of them like that Jer :)
 
premiumplus

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Some scope photos showing the distortion is on the negative swing of the waveform

Okay, here are some photos.
1. Left channel, with load, driven at 218Hz to about 2.9 volts output.
I tried both my loads, and it made no difference in the waveform whether it was purely resistive or a somewhat inductive load.
2. Right channel, with load, same conditions as (1)
3. Left channel, unloaded.
4. & 5. picture of dc protect board, installed. The zoebel network resistors look good, and there is no fault on the foil side, they're well soldered and suffered no damage in transit.

Notes:
1) I've gone through the PL-14 driver board up to the main driver transistors, and all of the semiconductors on the left channel are ok. I haven't tried tracing with the scope with the amp up and driving a load. I'm exhausting my other options first because I am paranoid of slipping probe syndrome! Plus I haven't
2) I checked the RCA 410 driver on the negative bank of the left channel and it looks good too.
3) I checked the power supply again, and I have +/- 108 vdc at the output transistor banks.

What is going on in picture #1? When I unload the channel the lower half of the waveform returns to normal.
I did try substituting the old Zoebel network across the output and it made no difference.
I must have a problem with a bad output transistor, since the driver is ok. I guess the next logical step is to check the outputs, then pull them except for one per bank, and then test it again with a load? It doesn't take much drive at all to produce the distortion...

Thanks, guys! This amp is going to be singing before the day is over or I'm out of coffee!!!

DSC_5651_3803.jpg DSC_5649_3802.jpg DSC_5652_3804.jpg DSC_5653_3805.jpg DSC_5654_3806.jpg
 
laatsch55

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Pull one leg of D9 or D10, that isolates the protection circuit of Q8,Q9. see if it goes away then. Also check D13 out of circuit, it tests low both ways in circuit.
 
laatsch55

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Another thing that can cause that is somethiing between the socket and the chassis. Small filing, piece of wire or solder, a lead cut, all can drive you crazy..
 
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Got called out a minute ago, a 45.7 ohm Zoebel resistor is not enough, especially with Don's board in there, it needs to be north of 5 and preferably closer to 6. But at least 5.
 
Gepetto

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premiumplus said:
Okay, here are some photos.
1. Left channel, with load, driven at 218Hz to about 2.9 volts output.
I tried both my loads, and it made no difference in the waveform whether it was purely resistive or a somewhat inductive load.
2. Right channel, with load, same conditions as (1)
3. Left channel, unloaded.
4. & 5. picture of dc protect board, installed. The zoebel network resistors look good, and there is no fault on the foil side, they're well soldered and suffered no damage in transit.

Notes:
1) I've gone through the PL-14 driver board up to the main driver transistors, and all of the semiconductors on the left channel are ok. I haven't tried tracing with the scope with the amp up and driving a load. I'm exhausting my other options first because I am paranoid of slipping probe syndrome! Plus I haven't
2) I checked the RCA 410 driver on the negative bank of the left channel and it looks good too.
3) I checked the power supply again, and I have +/- 108 vdc at the output transistor banks.

What is going on in picture #1? When I unload the channel the lower half of the waveform returns to normal.
I did try substituting the old Zoebel network across the output and it made no difference.
I must have a problem with a bad output transistor, since the driver is ok. I guess the next logical step is to check the outputs, then pull them except for one per bank, and then test it again with a load? It doesn't take much drive at all to produce the distortion...

Thanks, guys! This amp is going to be singing before the day is over or I'm out of coffee!!!
Click to expand...
Hi Dave
What's up with the 3 grounds going into the 2nd pin between the AC terminals of the DC protect? It is bad to run any of the amp signaling wire into that pin. That pin should be a single wire over to the single point ground, nothing else. Where are those 3 wires originating from?
 
Gepetto

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What output transistors are you running above the RCA410 transistors?

Do you have clearance underneath the DC protect board and the tips of the fuse holders? Looks pretty close in your photo.
 
premiumplus

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laatsch55 said:
Pull one leg of D9 or D10, that isolates the protection circuit of Q8,Q9. see if it goes away then. Also check D13 out of circuit, it tests low both ways in circuit.
Click to expand...
I isolated D9 and D10 and that made no difference, so the protection ckt is ok. Q 7 checks good. I'll pull D13 right now and get back in 5 min.
 
premiumplus

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Gepetto said:
What output transistors are you running above the RCA410 transistors?

Do you have clearance underneath the DC protect board and the tips of the fuse holders? Looks pretty close in your photo.
Click to expand...
MJ21196G, and there's about 3/8 inch clearance beneath the dc protect board and the fuse holder.
 
premiumplus

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Gepetto said:
Hi Dave
What's up with the 3 grounds going into the 2nd pin between the AC terminals of the DC protect? It is bad to run any of the amp signaling wire into that pin. That pin should be a single wire over to the single point ground, nothing else. Where are those 3 wires originating from?
Click to expand...
Per Don Imlay's instructions. Online at his site...

One end goes to the copper strap on the filter caps, one goes to the input jack gnd, and the other goes to pin 6 on the driver board.
Don said to cut the original wire going from the input jacks to the driver board, and add a wire from the filters, joining all 3 at input 6 of his board.
 
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