Odd voltages

[Retropin]

The power board in a Stern machine was pretty badly hacked, so i decided to replace it with a GPE one from RTBB.

I install the board ( my LEAST favourite job apart from crimping bally /Stern female connectors)

Game no longer works. OK, i think, out comes the DMM and check voltages - ALL are higher than should be present - 43v solenoid is 65v etc.
Testing across E points reveals wild voltages from the transformer. Instead of 173V im getting 250V, which REALLY concerns me as i now have mains potential.
Much head scratching later, i curse the damn machine and walk away from it swearing to come back another day and sort it out.

Time to move onto the GTB Spiderman which also has power supply faults.
New zener, few resistors, diodes etc later, plus all ground mods done, i install J1(?) and test voltages on power supply. Once again - all voltages are higher than they should be.
WTF im thinking what the hell is going on?
5V is 6.5V
8V is 11V
60v is 75v
etc etc etc.

How this is, i dont know as the power supply is 2 seperate circuits and one should not affect the other.
Pull it apart for the umpteenth time, rebuild again, checking everything - same result


Absolutely deflated, i walk away from 2 machines. Nothing makes sense anymore, wheres my EM's? No problem with those.

Anyway, my dad is over from UK for Xmas - an electronics engineer from the 50's onwards and we tackle this together.
10 minutes later - he is scratching his head..."doesnt make sense" he says - YUP! I know that.

So as a LAST resort - we actually check the mains voltage. Sounds stupid i know, but we had exhausted every other avenue.
Mains voltage reads 1000V!!
Bullsh*t we both say....grab an anologue meter and test - 230V

Go to Spiderman and all voltages are present and correct...go to Stern game and all voltages present and correct.

Moral of the story???

Get your dad to fix em!.....Or never put too much faith in a DMM!

[Marty Machine]

Ouch !... 1000v mains would be something to see 

I realise digi-Meters are a pain in high noise/RF areas and 'play up' but i can't imagine anything noisy enough in a pin to upset a meter? unless you have installed a custom switchmode that's generating hash everywhere???
or the mpu crystal somehow is generating something that the meter doesn't like, but i wouldn't expect that.

As a matter of interest, can u put a NEW battery in your Digi-meter, and take voltage readings again?
It's be nice to confirm what the hell's going on there..... hopefully 1000v now reads 230vac 

Running outta theories....

Marty.

[ajlaird]

As a matter of interest, can u put a NEW battery in your Digi-meter, and take voltage readings again?

Yes, that would be my guess.

[Ballywannabe]

Been there, done that...

With a cheap DMM I used to get all sorts of funny readings - I learned to turn it off and try again.  Flat batteries are another good way to get weired readings

cheers
Ian

[Strangeways]

 

The only DMM I ever trusted was my $300 Fluke.. I had it for 14 years... Now I have a cheaper DMM and I don't trust it.

[Marty Machine]

Yep, my fluke will fade and blink (with flat batt) before even thinks about giving misreadings, as opposed to a cheapy that can't wait to trick you