Vectrex Problem, -13 volts issue

[vtk]

Hi Guys,

 

I have a vectrex unit here which is not powering up

 

It is a very clean unit (no dust or dirt inside), it looks like whatever the problem with it is, it happened early in its life, and then the vectrex has been stored since then

 

first checked fuses (in main plug and also internal vectrex fuse) = OK

 

so what happens is, when i plug in the vectrex to the mains, there is the normal hum sound from the transformer

 

if i use the vectrex power/volume switch to turn on the unit, the vectrex does not power up, instead the screen stays black.

the system does not boot up, there is no game audio sounds.

there is neck glow on the crt tube.

coming out from the speaker, there is some audio: a quiet 'crackle' (dust in pot) sound if i rotate the volume knob up and down.

 

i checked volts going in and out of the vectrex power/volume switch, and read the same value going in and then out of the switch (it read 20v using my multimeter at the switch), so i believe the power switch is ok

 

when i first opened up the vectrex to inspect, i noticed that the socketed chip IC207 (the 6522 VIA I/O control device) was not in the socket correctly (it had not been pushed into the socket correctly on one side, and therefore not making correct contact) .. so i have pushed this chip back into the socket (but have not determined yet if this chip is faulty)

 

ok so after having a quick visual look around the pcb's for poor solder joints, i powered on the vectrex and tested the voltages at the power cable (J204) going from the power pcb to the logic pcb

 

here i got the readings:

yellow wire -5v = -4.97v

green wire GND = OK

orange wire +5v = +4.83v

red wire -13v = approx 1.5v to 2v (the readings jump around a little)

 

i checked that the J204 connector was ok, and then i decided to test the -13v with the J204 connector now unplugged from the logic board.

 

with the J204 connector unplugged, the -13v line then measured: -8v

 

i'm not really sure what to do next.. should i be looking at the IC207 chip, or looking at the -13v area of the power supply

 

if anyone has some suggestions for how to proceed or which components to test / areas to look at, please let me know, thanks!

Edited March 14, 2016 by vtek

[R.Cade]

It's not likely the chip would cause a problem with the power, especially once disconnected. I would start with the power supply, disconnected from everything else.

[vtk]

thanks ok,

im wondering perhaps i should follow what this person did:

http://int03.co.uk/blog/2016/01/31/vectrex-repair-black-screen-no-vector/

[R.Cade]

It's very common for the Vectrex to need a cap kit. I would start with that, it may fix the problem without troubleshooting further.

[vtk]

hi again i just had a bit of a go with it all and now taking a break

 

i noticed one of the diodes (D107) was bad so i changed that, and i changed cap C120 (i have not checked other nearby caps yet)

 

then measuring again, i now get -12.65v on the -13v rail... i still have the same problem of the vectrex not booting up/black screen

 

does anyone know, is -12.65v too low for the vectrex to start up?

 

[vtk]

ah nuts

 

i changed the DZ102 zener diode, and now i get these voltages at the J204 power connector:

 

-4.97v

+4.83v

-13.15

 

but... the vectrex is still dead (nothing on screen, no game sounds.. but neck glow at the crt tube). i notice there is a noticeable hum/buzz sound now though when plugged in/switched on (coming from the speaker or transformer.... unsure which)

 

if anybody has any ideas of what to check next please let me know (i'm not sure where to go next, eg. the logic board, the power board..? thanks )

[vtk]

hey again i have just noticed something ...

 

there is a single dot in the middle of the screen, if i turn up the brightness knob, you can see it, sitting still in the middle of the screen, doing nothing

[vtk]

actually i noticed the white dot is in the upper right center of the screen

i reseated the socketed chips, but that didnt help

then i replaced all the socketed chips with known working ones, and that did not help either

[Maraakate]

If the 6522 IO chip is bad this will not allow it to start, having a condition you describe (white dot with hum from speaker). Since you said it was lined up cockeyed it may have shorted the chip and destroyed.

 

I did find a replacement IC for this that I have tested and it does work fine for most games. The intro screen to Thrust gets a little wonky, but if you need it now, cheap, and want to verify the IC is W65C22N6TPG-14.

 

This chip can be found online rather cheaply. Let us know if it works for you. I haven't tested it to hell and back on many games, but the games booted OK and looked OK from a brief playsession.

[vtk]

hello maraakate thanks for the response

 

unfortunately i did replace the socketed 6522 with a known working one during the last efforts to fix the vectrex, but the problem did not go away

 

however, i wonder if the socket itself might be corroded or something like that, eg. dirty.. or poor contact/soldering

i remember i did spray some electrical cleaner into the socket to help, but maybe still not clean enough (i should have checked continuity of each leg of chip to underside of pcb socket solder point).. and also check for shorts

perhaps i should take a look at it again, thanks

Edited April 9, 2016 by vtek

[Maraakate]

Very possible. Or it could be a bad solder joint around that area too. Spray the contact cleaner somewhat judiciously on the socket then remove and reseat the IC (find one with the same pin count or one you can break pins off to make it the same) multiple times. Remove it, then let it evaporate out. Be careful inspecting the solder joints on this IC. I do remember that there are two or three lines that are bridged. This is on purpose. The first time I saw it I mistakenly thought that I dropped a solder blob and it found its way to that spot when doing a recap.

[Maraakate]

This might be more than you are willing to do, but since you have no scope... can you remove the logic board from a working system and swap them to see if it is a problem with the logic board or possibly a problem with IC401?

[vtk]

cool, i will remember that some of the lines are supposed to be bridged

 

just a digital multimeter here yes, no scope

 

hopefully i will try again and attempt your suggestions when i can (currently just trying to get better from heavy cold/flu)

[Funkyspectrum]

did you ever fix the problem, mate ? i have the exact same issue now :-( :-( :-(

[vtk]

hi, i'm afraid not, i had another vectrex which is working so i ended up just putting this non-working vectrex away in the cupboard