1986 Williams High Speed pinball repair system11 - low +5 volts

Added: 2026-05-09

[00:00:07]high speed tur it on does nothing like literally nothing like so much nothing that there's no coat on there which means it's not getting 5 volts go up to the power supply right here and these gray wires on this top connector are the 5 volts put my red lead on there black on ground you can see I got nothing now if I go over to this black with the white wire can see I gotus 12 volts and if I go over to this wire over here I think this white one I think it's also 12 it's plus 12 Vols and it got nothing if I go to this connector it's for the score displays the orange wire is -00 and we are getting uh I think we're getting minus 100 hold on a second um should be getting minus 100 there it is come on baby 100 yep and then the black wire next to it is plus 100 so the score displays are getting power up just no 5 volts this fuse I think it's a coil fuse that was blown I took out this is the 5V fuses I checked these are all good these are all good so we have some sort of problem this is this power in from the Transformer this is the power out so something's wrong with the power supply so I got the power supply out the only connector I have a hat this this big square one that's the input from the trans Transformer so this is the bridge rectifier that takes that ultimately takes 12 volts and converts it to from AC to DC so here you can see now the board is marked positive that's a positive lead this is the negative and then these are the two AC's so if I have my meter on AC see I'm getting 10 volts on that lead 10 volts on that lead that's good switch my meter to DC go over to the Plus lead and I'm getting 13 volts so the bridge rectifier is in fact working now the other thing let me turn this off other thing that I always do on these so I always replace these two little caps here they're very close to this power or heat sink and they get baked so I always replace those I've already done that and we're still not getting 5 volts out so there's some other issue the schematics these are the two caps I changed one was C7 you can see it's right in line if that goes open it won't work likewise C8 same deal in line it doesn't go really between grounds it goes between the AC and the plus so those things got to work order to replace those but here's this chip this uh uh 723 PC we should check the inut voltages so at Pin five we should have about plus 5 and pin 6 + 7 so let's go over here 1 2 3 4 five and we have we have five six 7 and we have oh wait six we have seven so the input voltages this chip are good now let's look at the output side we want to look at Pin 10 let's see that's 7 8 910 we got 5.6 and it's saying that we should have 6.47 so it's a little low but not too bad but the main one we want to look at is um let's see the one that is right here pin two try that and pin two was good at 7 Vols that's perfect um and then that goes up to this diode and then the other side of the diode should give us about 5 Vols and it does so and if I go to the emitter of the big transistor right here look there's my 5 Vols so in theory this is where perfectly let's flip the thing over and I'll put it right on the output connector oh joy 4.97 H so power supply is good that means when I plug it all in something's dragging the 5 volts down put this on here with the connector off and look 497 volts that's exactly where it needs to be and then when I put this on and then we check it it drops down to less than one volt and we come over here disconnect CPU board power and check it again someone's still dragging it down 3 volts back I think it's the power supply that that these boards are okay they just I don't see any damage it's just a hunch I still think it's a power supply so what I did instead of replacing this cap I just jumpered in a new one and uh check the 5 Vols and it's still too low so it's not the cap that only leads me with this got it working what a pain in the butt but the bottom line was Bridge rectifier was bad so how did I determine that well tested it unload it it's fine but as soon as it was a load on the power supply the voltage 5 volts would drop down so what was really happening is that the 12vs AC that gets fed to this and then converted to 12 volts DC then ultimately gets fed to this guy that creates the 5 volts this was failing internally so what I did is right here on these little connectors here I hooked up a light bulb and without the light bulb on the power supply just not connected to anything I could see my output 5 volts was fine soon as I put the light bulb on here light bulb would dim down you could watch the 5 volts go you know just drop drop drop so I put a new bridge in and now it's all working working I should have taken a video of the light bulb thing but I didn't and here we are with our working high [Music] speed