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Vectrex blows internal fuse after time
- Thread starter bobmoo79
- Start date
daver2
10k Member
And the fuse this time when you power it up?
Dave
Dave
daver2
10k Member
Ok, we need to get serious now with this pesky machine...
Dave
Dave
daver2
10k Member
So, I have done a very, very simple absolute worst case calculation of the primary current.
I have looked up the current rating of the 1N5624 diode used in the full-wave bridge rectifier. This is quoted as 3A.
Assuming 3A at +9V and 3A at -9V gives us: (3*9) + (3*9) = 27 + 27 = 54W.
Approximately doubling this gives us a convenient 100W light bulb!
At 230V the current consumption for a 100W load (ignoring any surge) is 230/100 = 230 mA.
Therefore, a 250 mA fuse is absolutely believable.
I don't expect the current to get anywhere near this value though...
Let me think about how to progress...
Dave
I have looked up the current rating of the 1N5624 diode used in the full-wave bridge rectifier. This is quoted as 3A.
Assuming 3A at +9V and 3A at -9V gives us: (3*9) + (3*9) = 27 + 27 = 54W.
Approximately doubling this gives us a convenient 100W light bulb!
At 230V the current consumption for a 100W load (ignoring any surge) is 230/100 = 230 mA.
Therefore, a 250 mA fuse is absolutely believable.
I don't expect the current to get anywhere near this value though...
Let me think about how to progress...
Dave
daver2
10k Member
Is it relatively simple for you to disconnect the wires from EP104 and EP106 from either T102 or the printed circuit board (assuming T102 is external to the PCB)? This would disconnect the transformer and switch from the electronics. We can then see whether the fuse blows or not with no electronics actually connected. If the fuse does blow - transformer or switch or T102. If the fuse does not blow - we can measure the AC voltage derived from the transformer secondary by measuring between EP104 and EP105 (centre tap) and then between EP106 and EP105 (centre tap) and then between EP104 and EP106. The AC voltage read in the last step should be approximately the sum of the previous two (2) readings.
Don't forget to label each cable so you know where to connect it back to again...
Post the voltage readings back (and whether you needed a new fuse or not) and we will take it from there.
The next step would be to test the full-wave bridge rectifier out consisting of diodes D101-D104 and C101-C104. Now the transformer is disconnected, we should be able to do this quite simply with your multimeter. Do you have a diode check function on your multimeter?
Dave
Last edited:
daver2
10k Member
Excellent.
No excitement is good!
I will post the bridge rectifier test tomorrow. Masterchef is on now!
Dave
No excitement is good!
I will post the bridge rectifier test tomorrow. Masterchef is on now!
Dave
daver2
10k Member
My apologies. I have got embroiled in a potential major issue at work this afternoon and I am going out tonight.
However, as D101 through D104 are conventional diodes, you can test them with either the diode test function of your multimeter (if you have one) or with a multimeter set to read resistance. When the probes are put one way on the diode, it should exhibit a LOW resistance - and when the leads are reversed, it should exhibit a HIGH resistance. You repeat this test for each diode in turn.
You may get some 'odd' resistance readings from having the DC-side of the bridge rectifier connected to further circuitry downstream (e.g. the smoothing capacitors and voltage regulators).
Perhaps you can note down (for each diode) which way your leads are around and the resistance you read - and I can take a look at the results tomorrow?
Dave
However, as D101 through D104 are conventional diodes, you can test them with either the diode test function of your multimeter (if you have one) or with a multimeter set to read resistance. When the probes are put one way on the diode, it should exhibit a LOW resistance - and when the leads are reversed, it should exhibit a HIGH resistance. You repeat this test for each diode in turn.
You may get some 'odd' resistance readings from having the DC-side of the bridge rectifier connected to further circuitry downstream (e.g. the smoothing capacitors and voltage regulators).
Perhaps you can note down (for each diode) which way your leads are around and the resistance you read - and I can take a look at the results tomorrow?
Dave
daver2
10k Member
That's an even better test!
Just be careful when desoldering and flexing - otherwise you could end up with a 2-part diode (as some others have)...
Dave
Just be careful when desoldering and flexing - otherwise you could end up with a 2-part diode (as some others have)...
Dave
daver2
10k Member
Seems good to me also.
Dave
Dave
While I was soldering the diodes back I glanced at the wire mod I put in the back of the power switch and thought "I wonder...."
So I soldered those foods back and reconnected ep104 and ep106 and removed that wire mod.
The vectrex ran for an hour and a half before I switched it off. No fuses were harmed.
I guess my next logical step would be to reconnect the yokes and run it again, then the deflection circuit and try again, then finally the hv. Just to see if that wire was causing the issue all along.
Should be interesting...
So I soldered those foods back and reconnected ep104 and ep106 and removed that wire mod.
The vectrex ran for an hour and a half before I switched it off. No fuses were harmed.
I guess my next logical step would be to reconnect the yokes and run it again, then the deflection circuit and try again, then finally the hv. Just to see if that wire was causing the issue all along.
Should be interesting...
daver2
10k Member
So where did you actually solder the wires on the rear of the switch then I wonder?
I was hoping any problem with your wire modifications to the switch would show up with my test when we removed the two wires from feeding the AC supplies to the power board.
You could only have shorted out the two ends of the transformer windings, and that would have given no voltage on the power board, or when we measured the AC supply voltage either.
Dave
I was hoping any problem with your wire modifications to the switch would show up with my test when we removed the two wires from feeding the AC supplies to the power board.
You could only have shorted out the two ends of the transformer windings, and that would have given no voltage on the power board, or when we measured the AC supply voltage either.
Dave
I soldered a wire across ep104 and ep106 because the switch was not working properly. Corrosion/ tarnishing meant there was sound but no picture. When I ran your voltage test at ep104/106 with reference to 105 I had voltage on both 104 and 106. So my assumption is that all this switching the unit off and on has removed at least some of the tarnish. I'll check resistance in the switch later and hopefully get those other tests I mentioned done and report back.
daver2
10k Member
Ahhh...
If you had soldered a wire from EP104 to EP106 you are very lucky you didn't burn out the transformer... Basically, you have shorted out the transformer! I am even surprised that the Vectrex even partially worked at all and the fuse didn't blow instantly! Fortunately, the fuse did it's intended job in this case!
These are AC voltage points at EP104 and EP106.
When EP104 is positive (relative to both EP105 and EP106) then EP106 is negative.
When EP104 is negative (relative to both EP105 and EP106) then EP106 is positive.
The bridge rectifier then converts the AC voltage into DC voltage (with the assistance of the downstream smoothing capacitors) to give both positive and negative voltage rails (relative to EP105) which is the 0V/GND reference (centre tap of the transformer).
Perhaps I should have asked for a photograph of your wire modification first...
Dave
If you had soldered a wire from EP104 to EP106 you are very lucky you didn't burn out the transformer... Basically, you have shorted out the transformer! I am even surprised that the Vectrex even partially worked at all and the fuse didn't blow instantly! Fortunately, the fuse did it's intended job in this case!
These are AC voltage points at EP104 and EP106.
When EP104 is positive (relative to both EP105 and EP106) then EP106 is negative.
When EP104 is negative (relative to both EP105 and EP106) then EP106 is positive.
The bridge rectifier then converts the AC voltage into DC voltage (with the assistance of the downstream smoothing capacitors) to give both positive and negative voltage rails (relative to EP105) which is the 0V/GND reference (centre tap of the transformer).
Perhaps I should have asked for a photograph of your wire modification first...
Dave
Ah yes, I hadn't thought about that so treated it more like a dc voltage.
I should have provided a photo in my first post, or even better, the schematic showing the link (then even I might have spotted the issue).
Hopefully when i reconnect everything it'll just work as it should. I'll let you know how I get on.
Thanks again for all your help so far, I've certainly learned something from this experience. If you send me a dm with your email address I'll send you a little something for your time.
I should have provided a photo in my first post, or even better, the schematic showing the link (then even I might have spotted the issue).
Hopefully when i reconnect everything it'll just work as it should. I'll let you know how I get on.
Thanks again for all your help so far, I've certainly learned something from this experience. If you send me a dm with your email address I'll send you a little something for your time.
daver2
10k Member
>>> Thanks again for all your help so far.
No problem. That's what we are here for - helping out.
>>> Hopefully when i reconnect everything it'll just work as it should. I'll let you know how I get on.
Fingers crossed...
>>> If you send me a dm with your email address I'll send you a little something for your time.
No need. If we meet up someday - you can buy the first beer!
Dave
No problem. That's what we are here for - helping out.
>>> Hopefully when i reconnect everything it'll just work as it should. I'll let you know how I get on.
Fingers crossed...
>>> If you send me a dm with your email address I'll send you a little something for your time.
No need. If we meet up someday - you can buy the first beer!
Dave