(Topic ID: 206257)

Haunted House "Sound board issue?"

By Boltronix

4 years ago



Topic Stats

  • 6 posts
  • 4 Pinsiders participating
  • Latest reply 4 years ago by Boltronix
  • Topic is favorited by 1 Pinsider

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#1 4 years ago

Upon connecting the 30vdc power to the sound board the 1 amp sb fuse blows on the bottom cabinet. Sound was fine. When i adjusted THE volume pot on bottom cabinet i saw the 1 amp sb fuse cook. I have; replaced all sound board caps, measured ohm's on speakers and pot and all that seems well. I am thinking the output amp on the sound board is bad. I believe that is all the 30vdc is used for? Any comments advice are appreciated as I proceed troubleshooting.

#2 4 years ago

Hi,

Yes the 30 VDC is only used for the amplifier (LM379S).
All others voltages +/- 12vdc are for D/A converters (1408) and pre-amp. (LM741).
The A7 board (speech/sound power supply board) produce the regulated +/- 12 volts for converters, and the +30 volts for the amplifier.

The sound board had receive later some modifications:
On september, 1981, the "On-target newsletter" announce an improvement to provide higher volume level for sound/speech. They remove and replace some discrete components around the LM379S. Nothing very important here (they also improve the stability for the speech generator - but not installed on HH).
But, on july/aug. 1983, as the LM379S was no more produced, Gottlieb replace it by a TDA2002, mounted on a piggy-back. Of course, as the TDA2002 doesn't support the 30 VDC, they also made some modifications on the A7 power board. Only the "high-voltage" section was changed, to reduce the 30 VDC to 18 VDC to be compliant with the TDA2002 specifications.

Finding a LM379S today is very difficult. When the amp is dead, we use solutions based on LM1875 or something similar.

#3 4 years ago
Quoted from noflip95:

Hi,
Yes the 30 VDC is only used for the amplifier (LM379S).
All others voltages +/- 12vdc are for D/A converters (1408) and pre-amp. (LM741).
The A7 board (speech/sound power supply board) produce the regulated +/- 12 volts for converters, and the +30 volts for the amplifier.
The sound board had receive later some modifications:
On september, 1981, the "On-target newsletter" announce an improvement to provide higher volume level for sound/speech. They remove and replace some discrete components around the LM379S. Nothing very important here (they also improve the stability for the speech generator - but not installed on HH).
But, on july/aug. 1983, as the LM379S was no more produced, Gottlieb replace it by a TDA2002, mounted on a piggy-back. Of course, as the TDA2002 doesn't support the 30 VDC, they also made some modifications on the A7 power board. Only the "high-voltage" section was changed, to reduce the 30 VDC to 18 VDC to be compliant with the TDA2002 specifications.
Finding a LM379S today is very difficult. When the amp is dead, we use solutions based on LM1875 or something similar.

Impressive knowledge! I know who to contact if my HH ever has issues

#4 4 years ago

Note that the replacement of the rare LM379S has already been discussed here.
An there is a wiki (from ChrisHibler) for replacing by a LM1875 :
http://www.pinwiki.com/wiki/index.php?title=Gottlieb_System_80#Replacing_the_Obsolete_LM379S_Amplifier_with_a_Modern_Amplifier

I know a guy in France that has some LM379S in stock (about 15€ here). But to my mind, the LM1875 is better and more modern.

#5 4 years ago

Homepin made a nice board that took out all the hassle.

Not in stock anymore

https://rocklandpinball.com/product/gottlieb-audio-amp-lm379/

#6 4 years ago

Great input, Thanks!

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