V400 carnage

[David Forbes]

This clock had a hard life. The PC board was baked from the transistor overheating. There was also a carbonized spot to the left of the transistor, where the far end of the rectifier diode pad was placed very close to the transistor, with a ground plane in there too! 0.5mm spacing between traces with 200VAC on them. I don't know which was the chicken and which the egg.

[chuck richards]

That picture reminds me of a telephone answering machine
which mysteriously failed.

Upon taking it apart, I found out why it was keeping the
telephone line busy all the time.

The board had a big carbonized burned spot on it much like
your picture shows. Apparently, as far as I could tell,
there was a cockroach in there sitting across the traces
just when a lightning strike hit. It fried the roach across
the phone line conductors and burned the board black.

(oh the joys of living in the Florida swamp!)

It was a simple repair. I scraped the fried roach remains
off, and then went about carving down between the traces with
an exacto knife until I hit virgin board material.

Ohmed it out until is was open again, and afterwards it worked ok.

Chuck

$4.95/mo. National Dialup, Anti-Spam, Anti-Virus, 5mb personal web space. 5x faster dialup for only $9.95/mo. No contracts, No fees, No Kidding! See http://www.All2Easy.net for more details!

[Nick]

Its almost as if the V400 never existed! There is now almost nothing about it on the web - ISTR it was released in about 2006 - Dieter replaced it with the V600 series in about 2009...

I still think the best bet is to ask him...

Cheers

Nick 

[Dieter Waechter]

Hi,

Already answered directly. ;-)

Dieter

[Ciaran Wills]

Were you able to fix it?  I have a V400 that appears to have suffered the same fate, and I'd really like to get it running again.

[David Forbes]

I did fix this clock. I carved away the carbonized PC board and built a better
heat sink arrangement for the TO-220 transistor, and I reattached the burned
traces with wires. I made wider clearance between the HV power paths too.

I may have some photos of the repair job at home; I will look tonight.

> --
> You received this message because you are subscribed to the Google Groups
> "neonixie-l" group.
> To unsubscribe from this group and stop receiving emails from it, send an email
> to neonixie-l+...@googlegroups.com
> <mailto:neonixie-l+...@googlegroups.com>.
> To post to this group, send email to neoni...@googlegroups.com
> <mailto:neoni...@googlegroups.com>.
> To view this discussion on the web, visit
> https://groups.google.com/d/msgid/neonixie-l/e9fbe32d-740a-4b2d-b315-4ec3a676d902%40googlegroups.com
> <https://groups.google.com/d/msgid/neonixie-l/e9fbe32d-740a-4b2d-b315-4ec3a676d902%40googlegroups.com?utm_medium=email&utm_source=footer>.
> For more options, visit https://groups.google.com/d/optout.


--
David Forbes, Tucson, AZ

[gregebert]

Here's a handy online tool for determining PCB-trace separation:  http://www.smps.us/pcbtracespacing.html

There are 3 spacings noted (external, internal, and coated). I would recommend using 'external' wherever possible because it's the most conservative. Unseen flaws in PCB manufacturing happen, so using absolute-minimum spacing with high-voltage traces is a gamble.

The website mentions UL experiments that found PCB's can tolerate 40 volts/mil. One mm is about 40mils.

I dont advise pushing PCB designs anywhere near that value, though.

[David Forbes]

Unfortunately, I have no photos of the circuit board repairs.

--
David Forbes, Tucson AZ

[threeneurons]

On Saturday, April 19, 2014 at 3:05:50 PM UTC-7, nixiebunny wrote:

There was also a carbonized spot to the left of the transistor,... I don't know which was the chicken and which the egg.  

Over the years, I'ved had several experiences with charred PCBs. The most notable one was on power supply board, that was part of a larger system, that our company made. It looked like one of the tantalum caps ignited, and managed to get the epoxy fiberglass PCB burning, too. I could stick my hand thru the resulting hole ! This happened out in the "field", so how it occurred is largely speculation. One of our service techs brought it in. That board had several large 100uf tantalums on it. 94V0 rated, too :(

Another incident involved a 100W Marshall tube amp. I repaired it for a friend. When it came in, the power supply was being overloaded. It was too new of an amp, to already have bad caps. Found a short between the anode pin and one of the heater pins, of one of the EL34 tubes. The heater is grounded on this unit. Its not left floating. The short was caused by carbonized PCB between those pins. Don't know what initially caused it. I blame a small critter, like a roach. The owner's housekeeping skills aren't the best. Fixed it with an X-acto knife, by carving a slotted hole between those pins.