Aw poop! PL400 fried!

laatsch55

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My Fluke doesn't measure that low very well either, measure a 5 ohm resistor, the put it in parallel with one of the leads, any homage that's close will work. Resistance of leads and connections makes subohm measurements tough...
 
roccus

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laatsch55 said:
My Fluke doesn't measure that low very well either, measure a 5 ohm resistor, the put it in parallel with one of the leads, any homage that's close will work. Resistance of leads and connections makes subohm measurements tough...
Click to expand...
great tip Lee!
 
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MarkWComer said:
A little update, also I'd like to thank everyone for your suggestions and help:

Building was so much easier than repairing...

Visibly, the only damage to the backplane board was R44, but will check others as well as diodes. Funny: ALL the emitter resistors measured .7Ω- even the unused extra that was included with the original backplane kit package- and they're clearly marked .33Ω (checked them with two different DMMs...).

No visible damage to the right channel section of the control board or the right channel backplane, cautiously assuming that no damage was done there.

Q9 on the control board seemed iffy, but it's one of the germanium transistors and they're a bit leaky to begin with.

hFE testing of the left channel transistors confirmed what I already discovered, so that exercise was moot. I'll have to pull all the transistors anyway in order to do the step-by-step startup testing, so the right channel output transistors will be checked as well.

Nothing to do now except wait for the box from Mouser. Everything ordered except for the germanium transistors, and I should get some 1A fuses for the startup tests. Maybe a foolish hope, but I'm putting off ordering the DC protection board for now.

So, this just seems to be a spontaneous failure of a transistor that cascaded to other transistors causing the blowout on the control board- any thoughts on that theory?
Click to expand...
That is what happens if a transistor in totem pole config fails. Having the 5A AGX rail fuse in place keeps it from cascading.
 
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laatsch55 said:
My Fluke doesn't measure that low very well either, measure a 5 ohm resistor, the put it in parallel with one of the leads, any homage that's close will work. Resistance of leads and connections makes subohm measurements tough...
Click to expand...
4 wire meters with Kelvin connection are required for these low ohm measurements.
 
MarkWComer

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Does anyone know the part number for the IC on the DC protection board?

Don includes the IC with the bare board and the assembled kit. I have a list with Mouser's part numbers, the IC isn't listed.
 
laatsch55

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They are obsolete Mark, that's why Mouser doesn't have them. EBAY China sellers Mark.
 
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R25 on the REV D control board- seems to be an odd fish- unavailable unless I buy 500, and then they'd be on backorder. Tried other manufacturers, but they don't offer any 5.62k 2W resistor. What I found were Vishay with the same wattage, tolerance, and resistance (Mouser 71-CMF555K6200FHEK). The flag is that they're little brown suckers, not the blue ones with stripes.

Same story with R38/39 on the backplane boards. Mouser seems to be changing some of their stock numbers around.

They're... OK to use?

Ordered the components for the DC board excluding the IC, still have to get the germanium transistors ordered.
 
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MarkWComer said:
R25 on the REV D control board- seems to be an odd fish- unavailable unless I buy 500, and then they'd be on backorder. Tried other manufacturers, but they don't offer any 5.62k 2W resistor. What I found were Vishay with the same wattage, tolerance, and resistance (Mouser 71-CMF555K6200FHEK). The flag is that they're little brown suckers, not the blue ones with stripes.

Same story with R38/39 on the backplane boards. Mouser seems to be changing some of their stock numbers around.

They're... OK to use?

Ordered the components for the DC board excluding the IC, still have to get the germanium transistors ordered.
Click to expand...
R25 is either 5.6K or 5.62K 1/2W, not 2W, should be plentiful Mark.
 
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Mark, PM a list of what you need, If I'm gonna send an IC I can send the rest....
 
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First you need to eliminate the contact resistance of the ohmmeter connections, connect both probes to ONE resistor lead to get a baseline, then switch to the other lead of the test resistor to get the updated value, then subtract.

The ESR meters out there I have seen force you to zero every time they are turned on. tens of milliohms on two wire readings are pretty good. I generally use that instead of digging out my 4 wire.

Usually a 4 wire resistance reading is done, 2 wires push through the test current, and 2 other wires read the voltage across the resistor by connecting the high impedance voltmeter to the resistor leads at different locations than the test current leads. Been doing that professionally since the late 70's.

Poor mans improvised check: get 20 to 490 ohms, and 12 volts. put the 20 to 400 in series with the unknown sub 1 ohm resistor and then the DMM set for current and on the 12 volts. There will be a current flow. write the current reading down

series circuit:
12v-----120 ohm resistor-----unknown sub 1 ohm resistor---------dmm set for current--------ground

(12v 12 ohms 1 amp 12 watts, 12v 120 ohms 0.1 amp 1.2 watts and so forth.)

remove the dmm from in series but leave the rest set up to allow the current to flow.

12v-----120 ohm resistor-----unknown sub 1 ohm resistor----------ground
.....................................^............................................^...................
.....................................|---dmm set for voltage----------|


The current will be SLIGHTLY different without the DMM in circuit, but not much.

Take the dmm and measure the VOLTAGE across your sub 1 ohm resistor.

at 1 amp current, volts across the unknown resistor will translate directly to ohms, 0.300v will be 0.3 ohms
at 0.1 amp current 0.030 volts will be 0.3 ohms.

apply ohm's law : volts divided by amps is ohms.

Way back when, I used constant test currents of TEN amps. Mercury Displacement Relays.
Trying to get THAT temperature stable over time was a real treat.
 
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laatsch55

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So this us what Dracula does when.the rest of us sleep....


Thanks MTF....good stuff...
 
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So, Mark.

Keep us posted on your progress. I know you are lost without your WOPL. This is why everyone needs at least two...just in case.

Might as well get another one and make it a Rev. E, or whatever the latest build is...and you would have a "backup"....or one "in stock" ...for such eventualities..
 
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Gepetto said:
R25 is either 5.6K or 5.62K 1/2W, not 2W, should be plentiful Mark.
Click to expand...
They're plentiful if I buy a lot of 500- and even then they're not stocked. I can get 5.6kΩ, I didn't know how crucial that additional .02Ω would be. I copied the part number from the BOM and pasted it into the search box at Mouser, just doesn't come up...

2W was a typo...
 
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MarkWComer

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ksrigg said:
So, Mark.

Keep us posted on your progress. I know you are lost without your WOPL. This is why everyone needs at least two...just in case.

Might as well get another one and make it a Rev. E, or whatever the latest build is...and you would have a "backup"....or one "in stock" ...for such eventualities..
Click to expand...
The idea was for the 400 to be my "exploratory" project before doing a 700. I still have high hopes of doing a 700.

I won a Denon POA2800 in the Phoenix lottery (2 years ago?) but when the 400 was completed I got spoiled. The WOPL was so much tighter in the bass, not muddy, and really rattled the windows the way I liked them to rattle. My niece's daughter was visiting from Georgia last Thanksgiving, spirited off two of my Bell & Howell 16mm FilmoSound projectors and the Denon amp. I really couldn't have predicted the WOPL failure, so the goods went with my blessing. The Denon was good and powerful, but not up to par. Spoiled!

Two Syd Barrett LPs came in the mail today... Sadness ensues...
 
MarkWComer

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markthefixer said:
First you need to eliminate the contact resistance of the ohmmeter connections, connect both probes to ONE resistor lead to get a baseline, then switch to the other lead of the test resistor to get the updated value, then subtract.
...
Click to expand...
Oy Vey! Yes- I get the math, never occurred to me to do that trick. Ohm's law in action.
 
Gepetto

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MarkWComer said:
They're plentiful if I buy a lot of 500- and even then they're not stocked. I can get 5.6kΩ, I didn't know how crucial that additional .02Ω would be. I copied the part number from the BOM and pasted it into the search box at Mouser, just doesn't come up...

2W was a typo...
Click to expand...
Not crucial Mark. 5.62K was a sub when 5.6K 1% was out of stock at disti.
 
MarkWComer

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SilPads have added another hole! What's my risk of arcing through it?

IMG_0446_33.jpg
 
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