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Vectrex blows internal fuse after time
- Thread starter bobmoo79
- Start date
daver2
10k Member
I think I have worked out your failure mode now (hindsight - a wonderful thing)...
Let us assume that the switch feeding the AC voltage supply to EP104 fails and goes open circuit.
In this case, you will not measure any AC voltage at EP104 (relative to EP105), but will on EP106. I would have thought - with this failure mode - the the Vectrex should still have worked - even though it may have been a bit 'ropey'. Both DC supply rails (+ and - 9V) should be present - but only the half-wave rectified versions rather than the full-wave.
If you now join EP104 to EP106 with a piece of wire - the Vectrex (to my way of thinking) would still only work in the same way as previously.
Anyhow, in this case, the fuse should not blow.
If the switch (after a period of time) then started to work and conduct once again - you would then either have a direct short circuit across the secondary windings of the transformer - or a high current flow in the secondary windings of the transformer (depending upon the resistance of the partially working/faulty switch). In this case, once the current exceeded the rating of the fuse, it would blow.
That is my current thought of course.
You can repair these switches by taking them apart. But, watch the videos first! They contain little springs that jump out if you are not careful... You will also need the photographs of how to reassemble the parts.
If the switches can't be repaired, the best thing to do would be to unsolder the wires from the switch totally and connect the wires together correctly (using solder and some heatshrink tubing) and affix a label to the case indicating that the ON/OFF switch is inoperable and that the unit should be unplugged from the mains when not in use.
Dave
Let us assume that the switch feeding the AC voltage supply to EP104 fails and goes open circuit.
In this case, you will not measure any AC voltage at EP104 (relative to EP105), but will on EP106. I would have thought - with this failure mode - the the Vectrex should still have worked - even though it may have been a bit 'ropey'. Both DC supply rails (+ and - 9V) should be present - but only the half-wave rectified versions rather than the full-wave.
If you now join EP104 to EP106 with a piece of wire - the Vectrex (to my way of thinking) would still only work in the same way as previously.
Anyhow, in this case, the fuse should not blow.
If the switch (after a period of time) then started to work and conduct once again - you would then either have a direct short circuit across the secondary windings of the transformer - or a high current flow in the secondary windings of the transformer (depending upon the resistance of the partially working/faulty switch). In this case, once the current exceeded the rating of the fuse, it would blow.
That is my current thought of course.
You can repair these switches by taking them apart. But, watch the videos first! They contain little springs that jump out if you are not careful... You will also need the photographs of how to reassemble the parts.
If the switches can't be repaired, the best thing to do would be to unsolder the wires from the switch totally and connect the wires together correctly (using solder and some heatshrink tubing) and affix a label to the case indicating that the ON/OFF switch is inoperable and that the unit should be unplugged from the mains when not in use.
Dave
Dave, the machine ran happily for a couple of hours straight today so I think it's safe to say that particular issue is fixed.
One thing I noticed though is that it took a long time (about a minute) for the display to come on. This means the vectrex title screen has passed by the time you can see a display, so i presume this is longer than the manufacturer intended. I checked the back and the neck glow takes a long time to 'wind up'.
However, If turning it off and then on again instantly the screen comes up straight away.
if you turn off and wait a minute or two before turning it on then you're back to waiting for the display to come on again.
A quick Google search found several people suggesting the contacts in the power switch need cleaning. As i know this was definitely an issue previously that'll be my first port of call on this refurbishment. 🙂
the search found else somebody with the same/ similar issue, rectified by changing a diode.
forums.atariage.com
One thing I noticed though is that it took a long time (about a minute) for the display to come on. This means the vectrex title screen has passed by the time you can see a display, so i presume this is longer than the manufacturer intended. I checked the back and the neck glow takes a long time to 'wind up'.
However, If turning it off and then on again instantly the screen comes up straight away.
if you turn off and wait a minute or two before turning it on then you're back to waiting for the display to come on again.
A quick Google search found several people suggesting the contacts in the power switch need cleaning. As i know this was definitely an issue previously that'll be my first port of call on this refurbishment. 🙂
the search found else somebody with the same/ similar issue, rectified by changing a diode.
Vectrex screen takes 5 minutes to come up
I alway find tutorials about the "dot" appearing on the screen or how to calibrate the video... but for the life of me I cannot find one where they address the issue of a slow warm up. At start I can hear the music and sound but the sreen stays black, then after 5 minutes or so it plays just fine...
Last edited:
daver2
10k Member
The filament (heater) voltage is generated from the EHT circuit. Any reduction of the +/- 9V rails could affect the heater supply.
However, I would also check for damage to R529 (the 1W low value resistor in series with the heater). If this has gone high resistance, that will also affect the warm-up time.
Of course, the heater could have just aged...
I would measure the + and - 9V rails (immediately after switch-on) to see if they come up straight away or take a bit of time to build up.
Likewise, you could check the heater voltage itself across pins 3 and 4 of the CRT base. Don't forget this is an AC voltage. We can then compare this with the CRT specification.
Dave
However, I would also check for damage to R529 (the 1W low value resistor in series with the heater). If this has gone high resistance, that will also affect the warm-up time.
Of course, the heater could have just aged...
I would measure the + and - 9V rails (immediately after switch-on) to see if they come up straight away or take a bit of time to build up.
Likewise, you could check the heater voltage itself across pins 3 and 4 of the CRT base. Don't forget this is an AC voltage. We can then compare this with the CRT specification.
Dave
Sorry about the delay in getting back to you I've been ill and also very busy so just couldn't progress this for a while.
I've checked r529 and it is the correct value but the +9 and -9 inputs on T503 are actually measuring roughly +13v, -13v wrt the grounding strap.
I'll need to run this test again tomorrow though I measured after the display was already on, not during the period when it hasn't appeared yet.
I tried measuring the ac voltage across pins 3 and 4 of the tube (and at ep503 and ep504 in the power pcb) but got no cottage at all. This is with the vectrex running and displaying a picture so I must have done something wrong
I've checked r529 and it is the correct value but the +9 and -9 inputs on T503 are actually measuring roughly +13v, -13v wrt the grounding strap.
I'll need to run this test again tomorrow though I measured after the display was already on, not during the period when it hasn't appeared yet.
I tried measuring the ac voltage across pins 3 and 4 of the tube (and at ep503 and ep504 in the power pcb) but got no cottage at all. This is with the vectrex running and displaying a picture so I must have done something wrong
So I tried the measurement again.
+9v is about right (9.6v) until the point that the crt does a display, at which point it jumps to 12.5v
-9v starts at about -13v and status steady when the displays comes on.
Both measurements taken at the inputs to t503 with respect to the ground strap.
Something doesn't look right there......
Any idea what i was doing wrong with trying to measure voltage at the tube (pins 3 and 4)?
+9v is about right (9.6v) until the point that the crt does a display, at which point it jumps to 12.5v
-9v starts at about -13v and status steady when the displays comes on.
Both measurements taken at the inputs to t503 with respect to the ground strap.
Something doesn't look right there......
Any idea what i was doing wrong with trying to measure voltage at the tube (pins 3 and 4)?
daver2
10k Member
I agree, something doesn't look right. I'll have a think about that one later...
However, datasheets for the 240RB4 CRT indicates that the filament supply (on pins 3 and 4) should read 12V a.c.
However, there could be a problem in reading this supply with a conventional multimeter because the a.c. supply is derived from the EHT supply at a high frequency.
Dave
However, datasheets for the 240RB4 CRT indicates that the filament supply (on pins 3 and 4) should read 12V a.c.
However, there could be a problem in reading this supply with a conventional multimeter because the a.c. supply is derived from the EHT supply at a high frequency.
Dave
A bit of contact cleaner seems to have sorted that switch out.
The display starts up from cold in about 5 seconds now!
Fantastic.
Thanks again for all your help along the way Dave, I really do appreciate it. It's guys like you that make this hobby a pleasure to be involved in.
The display starts up from cold in about 5 seconds now!
Fantastic.
Thanks again for all your help along the way Dave, I really do appreciate it. It's guys like you that make this hobby a pleasure to be involved in.
daver2
10k Member
So, what must have been happening was either a bit of additional resistance on one side of the power supply (or a complete disconnection of one side of the power supply) for a period of time when the machine was turned on.
This could have resulted in the +/- 9V supplies being 'lopsided' in some way or another. I am guessing...
>>> Thanks again for all your help along the way Dave, I really do appreciate it. It's guys like you that make this hobby a pleasure to be involved in.
Absolutely no problem. This one was a good brainteaser anyhow!
Dave
This could have resulted in the +/- 9V supplies being 'lopsided' in some way or another. I am guessing...
>>> Thanks again for all your help along the way Dave, I really do appreciate it. It's guys like you that make this hobby a pleasure to be involved in.
Absolutely no problem. This one was a good brainteaser anyhow!
Dave
thunter0512
Veteran Member
Dave, you mentioned the 240RB4 datasheet. Could you please point me to a PDF copy of it?
daver2
10k Member
Well, not the true datasheet for the 240RB4 - but the manual for rejuvenating the CRT. It identifies the heater voltage and the type of adapter to use.
A 240RB4 CRT specifies a heater voltage of 12.0V and a test base of CR/CA 7.
Looking at the end of the document identifies the CR/CA 7 and what leads/pins corresponds to which electrodes.
I haven't (yet) identified the actual full datasheet.
Dave
A 240RB4 CRT specifies a heater voltage of 12.0V and a test base of CR/CA 7.
Looking at the end of the document identifies the CR/CA 7 and what leads/pins corresponds to which electrodes.
I haven't (yet) identified the actual full datasheet.
Dave
thunter0512
Veteran Member
I have seen that before. It seems strange that Google finds no actual datasheet.