TTI Board blew up and....

[Elmer]

We have a theater event in 2 days and our Theatre Techniques Inc. light
board just blew up. It is an MDS224 board. It looks very simple inside,
but a transformer and 2 of the power resistors burned up. I can replace
the power transformer, but the fire destroyed the color coding on the
power resistors. If anyone has any hints or clues or old schematics for
this unit, and could tell these values, I'd be grateful!

 

[[email protected]]

We have a theater event in 2 days and our Theatre Techniques Inc. light
board just blew up.

You might have better luck finding someone that has a manual for this
board by asking in one of the rec.arts.theatre newsgroups.

As far as figuring out the resistor values - have you measured the old
resistors, out of circuit, with a meter? The overheating will have
changed their values, but if they are not open circuit, you can at least
get an estimate.

One time in a hundred you get lucky and the resistor value is silkscreened
on the circuit board underneath it.

Can you tell what the resistors are doing in the circuit? Are they in
the power supply, or on one of the lighting channels, or...? If there
is more than one identical channel, compare the damaged channel to the
others.

If the resistors form part of a low-voltage power supply, and you
absolutely can't figure them out, you may be able to patch in an
outboard low-voltage supply, if you can figure out the voltage and
current requirements.

For further help on reverse engineering the board enough to figure out
the resistor values, you might ask in sci.electronics.repair .

There is some advice on diagnosing blown resistors (in a switching power
supply) at http://www.repairfaq.org/sam/smpsfaq.htm#smpsrnfntm .

I hope this helps!

Matt Roberds

 

[Elmer]

You might have better luck finding someone that has a manual for this
board by asking in one of the rec.arts.theatre newsgroups.

As far as figuring out the resistor values - have you measured the old
resistors, out of circuit, with a meter? The overheating will have
changed their values, but if they are not open circuit, you can at least
get an estimate.

One time in a hundred you get lucky and the resistor value is silkscreened
on the circuit board underneath it.

Can you tell what the resistors are doing in the circuit? Are they in
the power supply, or on one of the lighting channels, or...? If there
is more than one identical channel, compare the damaged channel to the
others.

If the resistors form part of a low-voltage power supply, and you
absolutely can't figure them out, you may be able to patch in an
outboard low-voltage supply, if you can figure out the voltage and
current requirements.

For further help on reverse engineering the board enough to figure out
the resistor values, you might ask in sci.electronics.repair .

There is some advice on diagnosing blown resistors (in a switching power
supply) at http://www.repairfaq.org/sam/smpsfaq.htm#smpsrnfntm .

I hope this helps!

Gee thanks for the reply, but the 2 resistors totally fried, as in
flames. I can see that one has a red band at the start and is 5%, the
other might have been something starting with a black or brown band, but
is so discolored and broken from its mountings as to render any reading
beyond that guesswork (and even what I think it is might be :-(

 

[Elmer]

Added crosspost to rec.arts.theatre.stagecraft

Dear Mr. Aglionby,

Sorry to hear about your board blow up. Don't know that two days is a
doable thing for anyone except those truly 'loaded for bear' in your area.

As another "T.T.I." in the business, we often get requests for dimmer
and console related information. We are not in any way related to the
other TTI folks - they are out of business. The standing link to the old
company and their products is now through Vara-Light/Dimatronics/Hub,
Inc., in Crystal Lake, IL. (815) 455-4400. Fax: (815) 455-1499. Do not
confuse them with Vari*Lite, the automated fixture company.

This information is five years old from Customer Service rep. Karen
Hansen and President Richard Latronica [we get many cross-referenced
customer calls]. They should be able to help out with the wiring color
coding, schematics, and any other questions you may have.

Hope this helps. If not, give me a shout out on a private phone, fax, or
e-mail chat at:

[email protected]
[email protected]
Ph/fx/ans: 202-332-4907

Regards,

Bert Morris, President
Theatrical Technicians, Inc.
2700 Connecticut Avenue, NW #109
Washington, DC 20008-5308
USA

Thanks for the info - it was a great help. I have a new transformer on
order and now I have some idea on the resistor values. Now all I have to
do is repair it and see if it works.

Wish me luck. Cheers!

 

[Elmer]

We have a theater event in 2 days and our Theatre Techniques Inc. light
board just blew up. It is an MDS224 board. It looks very simple inside,
but a transformer and 2 of the power resistors burned up. I can replace
the power transformer, but the fire destroyed the color coding on the
power resistors. If anyone has any hints or clues or old schematics for
this unit, and could tell these values, I'd be grateful!



Added crosspost to rec.arts.theatre.stagecraft

Dear Mr. Aglionby,

Sorry to hear about your board blow up. Don't know that two days is a
doable thing for anyone except those truly 'loaded for bear' in your
area.

As another "T.T.I." in the business, we often get requests for dimmer
and console related information. We are not in any way related to the
other TTI folks - they are out of business. The standing link to the
old company and their products is now through
Vara-Light/Dimatronics/Hub, Inc., in Crystal Lake, IL. (815) 455-4400.
Fax: (815) 455-1499. Do not confuse them with Vari*Lite, the automated
fixture company.

This information is five years old from Customer Service rep. Karen
Hansen and President Richard Latronica [we get many cross-referenced
customer calls]. They should be able to help out with the wiring color
coding, schematics, and any other questions you may have.

Hope this helps. If not, give me a shout out on a private phone, fax,
or e-mail chat at:

[email protected]
[email protected]
Ph/fx/ans: 202-332-4907

Regards,

Bert Morris, President
Theatrical Technicians, Inc.
2700 Connecticut Avenue, NW #109
Washington, DC 20008-5308
USA

Thanks for the info - it was a great help. I have a new transformer on
order and now I have some idea on the resistor values. Now all I have to
do is repair it and see if it works.

Fantastic! It works. Thanks for all your help.

 

[Torrance Bell]

I'm kind of curious as to what might have made it asplode in the first
place. Was the transformer just old, or might there be a screw rolling
around in it somewhere?

Torrance

 

[Elmer]

I'm kind of curious as to what might have made it asplode in the first
place. Was the transformer just old, or might there be a screw rolling
around in it somewhere?

Torrance

I think the tranny just up and died. All the components are reverse
mounted on the underside of the panel, so nothing rollig around could
have done anything.

But the real problem AFAICS was that someone had put in a much larger
fuse than called for, so when the tranny shorted it pumped lots of power
into the power resistors which simply flambéed. I replaced the tranny
and the power resistors, put in 1 amp fast blow (instead of the 2 amp
slo-blow), and it came back to life.

When replacing the tranny I did notice that it had been replaced once
before at some point in the past.

I originally had to get the board up and working for an event this
evening, but, as is so often the case, no one bothered mentioning the
last minute event on Wednesday evening. So it got a good test workout
last night.

 

[Torrance Bell]

I think the tranny just up and died. All the components are reverse
mounted on the underside of the panel, so nothing rollig around could
have done anything.

You're lucky that it didn't fry the whole rest of the system.

What's the final voltage and current rating past the transformer? If
it's being directly plugged into the wall, there's probably a standard
AC to DC converter consisting of xfmr -> full wave bridge rectifier ->
filter caps.

If you're adventurous, I suggest replacing the transformer setup
entirely with a regulated switched mode power supply.

Torrance

 

[Elmer]

You're lucky that it didn't fry the whole rest of the system.

What's the final voltage and current rating past the transformer?

That I don't know.

If
it's being directly plugged into the wall, there's probably a standard
AC to DC converter consisting of xfmr -> full wave bridge rectifier ->
filter caps.

It seems to have been a half wave setup.

If you're adventurous, I suggest replacing the transformer setup
entirely with a regulated switched mode power supply.
Torrance

It's an analog board near as I can tell. We'll go all digital when it comes to
replacement time.