What are typical output voltages expected of a Williams transformer...?

[RetroACTIVE]

http://forum.arcadecontrols.com/index.php?topic=52107.0

I've begun turning up my robotron board set... I'm starting with the transformer and psu board... so far no big suprises except one...

Looking across taps 11 and 12... the schematic indicates it should be 20VAC... I'm reading >26 VAC... Consequently the voltage @ pin 1 of BR2 is 36.6 ish Volts.... I measured it with my el-cheapo DVOM... ... I brought the board to work today...I'm going to probe it with the o-scope...

Just curious about what to expect... I want to be sure my transformer is ok before I go and start using it.

[grantspain]

transformers are not a regulated voltage so you could expect as high as 26vac on the 20vac winding,your circuit that smoothes and regulates the voltage to dc should stop any dangerous overvoltage from occuring

[Ken Layton]

It is very common for transformers to read much higher voltages when there's no load connected to it!
Of course, the quality, accuracy, and features of your particular volt meter will affect what you read coming out of the transforrmer too. If you have a digital voltmeter, you need one that reads "True RMS" ac voltages.

[RetroACTIVE]

transformers are not a regulated voltage so you could expect as high as 26vac on the 20vac winding,your circuit that smoothes and regulates the voltage to dc should stop any dangerous overvoltage from occuring

It is very common for transformers to read much higher voltages when there's no load connected to it!
Of course, the quality, accuracy, and features of your particular volt meter will affect what you read coming out of the transforrmer too. If you have a digital voltmeter, you need one that reads "True RMS" ac voltages.

Thats what I figured... I brought it to work and used a Fluke 77... along with a digital o-scope ... Everything looks pretty good...even w/o load.

For  +5 I'm reading +4.92
For   -5 I'm reading - 5.00
For +12reg I'm reading + 11.8
For -12unreg I'm reading -14 ish
For +12unreg I'm reading 14 ish

For 6.3VAC I get 7.2 ish
For 27VDC unreg I get 36 ish

Its been a while since I've picked up these tools... I'm a software engineer by day... The hardware people in the lab are wigging out... everyday @ lunch I'm either re-working boards or like today... got all kinds of equip out and testing out the PS...

Thanks for the help.

[grantspain]

if your 5v dc is reading 4.92 at the psu you will need to turn it up to around 5.10 reading at the board edge connector otherwise you may have graphics/reset problems

[D_Zoot]

... Everything looks pretty good...even w/o load.

For  +5 I'm reading +4.92
For   -5 I'm reading - 5.00
For +12reg I'm reading + 11.8
For -12unreg I'm reading -14 ish
For +12unreg I'm reading 14 ish

That +5 *might* be a little problem.   Analog supplies don't regulate well without a load, so that's probably why it's a little low right now.  Recheck it at the game board after you get everything hooked up.

Those old Williams power supplies didn't have any adjustment provisions (except changing the resistance of one resistor on the supply board) and over the past 25+ years components can shift value slightly and cause the output voltage to drift one way or another.  If your +5 is still below 5.0v when the board is hooked up and running then it would probably be a good idea to rebuild the PS board as well.

But then again, the game board might be happy with slightly low +5,  if it runs, no graphics glitches and doesn't reset then you could run with it!


D

[Ken Layton]

Williams had a problem with the 6.3 volt AC section of the transformers. Some of the transformers were putting out 7.0 to as high as 9.0 volts. This winding of the transformer was used for the 6 volt coin door lamps and that's too high of voltage for the original 6.3 volt lamps to take.

Williams had issued a service bulletin about it years ago. If you have one of those that outputs too high of a voltage under a load of two #44 lamps then they suggested going to 12 volt bulbs instead.

[RetroACTIVE]

Williams had a problem with the 6.3 volt AC section of the transformers. Some of the transformers were putting out 7.0 to as high as 9.0 volts. This winding of the transformer was used for the 6 volt coin door lamps and that's too high of voltage for the original 6.3 volt lamps to take.

Williams had issued a service bulletin about it years ago. If you have one of those that outputs too high of a voltage under a load of two #44 lamps then they suggested going to 12 volt bulbs instead.

My 6.3V winding is definitely greater than 7

Thanks Ken!  Boy do I wish I had your experience and knowledge base... I'm going into this blind... hoping that all of the docs I've managed to scavenge are accurate.