K
kreed
Guest
On Dec 6, 2:47 pm, Bob Parker <bobp.deletet...@bluebottle.com> wrote:
in the very early 1980's I recall doing the occasional repair jobs for
a bloke (now retired 16 years back) who amongst other things, had a
quantity of coin-operated video games in bars and shops. One day I
remember having to service a game called "asteroids" that had a
"vectorbeam" or "XY" monitor (For those unfamiliar with this long
forgotten? technology - there isnt any raster scan, the deflection
coils are driven directly by amplifiers that are driven via 2 separate
D/A converters on the logic board, kind of like a CRO.
After a bit of stuffing around, we discovered that he had a spare
logic board of the same game, but made by a different manufacturer, so
we decided to try it. All was not well, the CPU was running and we
could see the game on the monitor, but the picture was shaking like
mad in both directions. Just as I was sticking my head in the back of
the machine to try and diagnose the fault, there was an almighty
"BANG" like a gunshot, followed by a second "BANG" a few seconds
later. Both were so loud our ears were ringing and sore for the next
hour or so.
Turned out the logic board had an onboard power supply providing +/-
12v for the D/A converters, and the AC was fed directly from a power
transformer to the board. Only problem was that one board had 4700uf
16v caps on it, and the other had 25v caps on it, and one cabinet had
a much lower secondary voltage coming from its transformer than the
other.
when swapped - BANG !
I learned a very important lesson about the dangers of electrolytics
that day, fortunately havent had a repeat.
On 6/12/2007 13:11 Alan Rutlidge wrote:
Sometime back another young poster to this NG had a similar experience with
an exploding electrolytic.
Difference was it hit him square in the forehead, leaving a crosshair
pattern resembling the vent release on the top of the cap.
Lucky he didn't cop it in an eye !
Cheers,
Alan
I installed a 10uF electrolytic backwards in an amp I was repairing
once. It was a bypass cap on an STK package.
There was a very loud bang as I was leaning over the unit, and the
cap's can flew past my face, missing my eye by maybe an inch before
hitting the ceiling then bouncing around the room.
Nice to know I'm not the only one's who done that.
Bob
in the very early 1980's I recall doing the occasional repair jobs for
a bloke (now retired 16 years back) who amongst other things, had a
quantity of coin-operated video games in bars and shops. One day I
remember having to service a game called "asteroids" that had a
"vectorbeam" or "XY" monitor (For those unfamiliar with this long
forgotten? technology - there isnt any raster scan, the deflection
coils are driven directly by amplifiers that are driven via 2 separate
D/A converters on the logic board, kind of like a CRO.
After a bit of stuffing around, we discovered that he had a spare
logic board of the same game, but made by a different manufacturer, so
we decided to try it. All was not well, the CPU was running and we
could see the game on the monitor, but the picture was shaking like
mad in both directions. Just as I was sticking my head in the back of
the machine to try and diagnose the fault, there was an almighty
"BANG" like a gunshot, followed by a second "BANG" a few seconds
later. Both were so loud our ears were ringing and sore for the next
hour or so.
Turned out the logic board had an onboard power supply providing +/-
12v for the D/A converters, and the AC was fed directly from a power
transformer to the board. Only problem was that one board had 4700uf
16v caps on it, and the other had 25v caps on it, and one cabinet had
a much lower secondary voltage coming from its transformer than the
other.
when swapped - BANG !
I learned a very important lesson about the dangers of electrolytics
that day, fortunately havent had a repeat.