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Old 10th December 2012, 07:22 AM   #81
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but yea other equipment I guess sockets to PCB may not be as drastic but still all that heat and expanding can't be good lol
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Old 10th December 2012, 08:30 AM   #82
12E1 is offline 12E1  United Kingdom
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Originally Posted by richwalters View Post
Here is the proof I'm so against PCB's.....this section of a power supply board, failed. The wirewound resistor despite being heat scorched still has the correct resistance; the fault occurred in the copper track which ran under it. After years of expansion/contraction from the heat, the track finally fractured.
Unsuprisingly, many computer aided pcb designs fall right into this trap.

richy
Why unsurprising? It is nothing to do with the fact that the design may or may not have been computer aided, or on a PCB. It is do do with the fact that the designer(s) did not place the parts correctly relative to one another, and quite probably under-rated the wire-wound resistor. That can happen just as much with a point-to-point design.

I have used PCBs and point-to-point (and have also laid out many analogue and digital PCBs profesionally - from 1 to 10 layers). The end result using either technique is always only as good as the care and understanding that goes into the process.
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Old 10th December 2012, 08:55 AM   #83
freax is offline freax  Australia
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Originally Posted by 12E1 View Post
and quite probably under-rated the wire-wound resistor. That can happen just as much with a point-to-point design.
looks pretty under rated to me, it also looks like the resistor was placed on the underside of the pcb and the heat has risen up to scorch the board from underneath.

Conceivably the designer has decided that cost was a serious factor and used a lower value OR that having the resistor mounted to the chassis or ontop of the pcb was too much of a hassle.

So even if he did rate the component properly he would have still screwed up on the fact that the resistor was on the underside of a pcb board, very strange behaviour indeed.

But not strange when you consider that corporations are using the planned obsolescence guidebook and following it to the letter.

This my fellow gents is sabotage, pure and simple cold blooded sabotage.

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Last edited by freax; 10th December 2012 at 09:08 AM.
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Old 10th December 2012, 09:52 AM   #84
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Well he said the resistor still had the correct resistance surprisingly after that much scorching you would think it would of drifted somewhat but the factors of age and time plus that heat expanding/contracting just weakened the trace etc
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Old 10th December 2012, 09:54 AM   #85
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mounting things further off the board is a good idea in my opinion if there is enough room to allow it that is
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Old 10th December 2012, 10:26 AM   #86
M Gregg is offline M Gregg  United Kingdom
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If valves are mounted to a PCB,

I prefer to use surface mount sockets and support the PCB with stand offs that support the tube bases and hard wire to the board..

If you are a superfi guy/gal then the question is sometimes raised does the fiberglass dielectric effect sound acting as a cap between tracks..for a normal build this is less of a problem..(If it is a problem) Whats the point of silver lead out caps connected to a copper track on a PCB?

I still like PTP even on a plain PCB or using the copper to solder mount the tag strip. use the copper as a screen to keep heater wiring shielded.

Hot parts and valve bases create dry joints when one part of the connection is fixed and the other moves with expansion. Perhaps Ok with preamp tubes and hard wire power tubes.. I still think of a PCB a temporary (X years)compared to a PTP build. In industry PCB is the standard now however component change is always a problem with age lifting tracks. Then again if I was building SS then PCB is the way to go. Nothing wrong with PCB as a sort of discrete component in a PTP build.

You can also mount the copper covered PCB inside a wooden case and this gives the effect of a top plate that can be earthed and the tag strip soldered onto the copper no screws to worry about..

I never thought about microphonics compared to PTP and PCB..I did melt candle wax over a PCB for a laugh...its strange how you convince yourself that the treble sparkle had all gone..I wasn't happy untill I stripped the wax off the board..LOL..I tried it after using black tack under caps etc just for fun..

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Old 10th December 2012, 11:29 AM   #87
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Originally Posted by freax View Post
looks pretty under rated to me, it also looks like the resistor was placed on the underside of the pcb and the heat has risen up to scorch the board from underneath.

Conceivably the designer has decided that cost was a serious factor and used a lower value OR that having the resistor mounted to the chassis or ontop of the pcb was too much of a hassle.

So even if he did rate the component properly he would have still screwed up on the fact that the resistor was on the underside of a pcb board, very strange behaviour indeed.

But not strange when you consider that corporations are using the planned obsolescence guidebook and following it to the letter.

This my fellow gents is sabotage, pure and simple cold blooded sabotage.

Click the image to open in full size.
Look under a Jap/chinese TV from the 1980's....shock and awe...one isn't alone in modifications and it goes on all the time on the PCB under. I've seen this done on the best music consoles too !

Last edited by richwalters; 10th December 2012 at 11:30 AM. Reason: miss
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Old 10th December 2012, 12:05 PM   #88
12E1 is offline 12E1  United Kingdom
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Well he said the resistor still had the correct resistance surprisingly after that much scorching you would think it would of drifted somewhat but the factors of age and time plus that heat expanding/contracting just weakened the trace etc
No. If it's a wire-wound, then the resistance may change only a very little despite the part reaching very high temperatures. The simple fact is that it got hot enough to burn the board and to apparently melt the solder joints (judging by their appearance) and that's down to the component rating and its placement.

Of course, it could be that it only got that hot due to a fault condition elsewhere, but that could also potentially have been anticipated and dealt with in the design. Again, nothing to do with PCB vs point-to-point construction.
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Old 10th December 2012, 01:36 PM   #89
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Quote:
Originally Posted by richwalters View Post
Here is the proof I'm so against PCB's.....this section of a power supply board, failed. The wirewound resistor despite being heat scorched still has the correct resistance; the fault occurred in the copper track which ran under it. After years of expansion/contraction from the heat, the track finally fractured.
Unsuprisingly, many computer aided pcb designs fall right into this trap.

richy
That resistor while it might be in spec was under rated for the application (or something is wrong with the circuit) No one in their right mind would choose a resistor of low enough wattage that actually distorts from the heat. If they had chosen a higher wattage resistor, they wouldn't have damaged the PCB. I'm surprised the resistor isn't destroyed because it sure looks like it is.

In short, it is either a malfunction in the circuit, or a error on the designer's part. The pcb is fine,
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Old 10th December 2012, 01:54 PM   #90
marce is offline marce  United Kingdom
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Unsuprisingly, many computer aided pcb designs fall right into this trap.
The computer dose not design the PCB the person in front of the computer does! This statement is both misleading and misinformed.
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