Vectrex Repair (another no buzz 3GE version)

[demonlg]

4 days ago i have only changed both 2n3905 , integrator caps and socket of both 34001, but the problem not resolved...at this point i have to replace socket of other remain chips, or i reball solder points of it....

It's the finger issue a very mystic problem. i have tested both 34001 with new, but not resolve.

If i put totally finger on top of 34001 all vectors going out to top right corner of screen and when i remove finger it return slowely in correct position!

Question, the little compensator capacitors 10nF (104) from power line 5v and gnd instslled to all chips, can it cause this type of problem (finger problem)?

 

[demonlg]

I have readed again discussion and before find the 7905 faulting i have socketed 4066, 34004 and 4052 on post 27, then i jave replaced 7905 and noted the problem of distortion at cold, and in post 59 i have the same square vector out of correct position.....at this point the problem is probably bottom of 4066, 34004 or 4052....

 

[demonlg]

And today at cold.........bahhhh

 

[daver2]

What did I say...

Dave

 

[demonlg]

Yes dave, now i jave used phon to hot this zone and all going to perfect working, then i have sprayed wirh cold air in same zone and again going complete distorted, the problem is here....i think so the sockets, originally not present for all four chips, generate a capacitance or is another issue in this zone, or 104 caps or zener diode or resistor, now i remove all socket and test all other component one to one at cold and hot ....

 

[daver2]

Please do NOT remove the sockets (if you haven't already). Adding a socket should NOT make any difference to the performance - unless you messed up the original desoldering and soldering.

Better to use hairdryer and freezer spray to isolate the problem to one component and then to fully check the connections one at a time with a multimeter.

If evidence of a solder issue, then is the time to warm up the soldering iron - but only then.

Dave

 

[daver2]

Some of the soldering (for example, on the left lead of C307 in your photograph) could be neater.

Please post some close up photographs of the top and bottom of the PCB (around this area) in good light and focused so I can make some suggestions about tidying up the solder joints etc.

Dave

 

[demonlg]

Hi Dave,
too late, I disassembled everything, desoldered everything, removed the sockets and reassembled everything without the socket, and I found the socket in the photo of the 34004 with pin3 (GND) bent as you can see! Once everything was reassembled I turned it on and it was perfect, still that square of the DEFLECTION PROTECT screen with the left part moved but much less, and shortly after turning it on it was almost OK, I redid the DAC OFFSET adjustments (without an oscilloscope only a multimeter because 'I didn't have it nearby) and after less than 2 minutes it was already ok. I was there and I also cleaned the area that you told me was dirty, it was fluxing, and I changed the 1n4148 diode on the Z axis output. I left only the 4066 and the 1808P8 socketed which was already socketed before I opened it for first time. Now let's see what happens tomorrow. It seems very strange to me but this is what I found. The whole story will follow eventually!

 

[daver2]

Ah, pin 3 is a non-inverting input to one of the OPAMPS. If it was just resting on a solder pad (and wasn't soldered) that would account for all of your problems.

Didn't you notice when you soldered the pins of that IC socket that one of the pins was not poking through the PCB?

Yes, flux and dirt needs to be cleaned off after soldering.

Your 'finger' should not 'work' now any more...

Dave

 

[demonlg]

Nothing, again same issue...i have to check again in this zone.....probably the pin is not the cause.

 

[daver2]

It won't have helped though...

Dave

 

[demonlg]

It's arrived second Vectrex, tomorrow i open it, and check what version is it.... then try to connect logic of this on my monitor e vice versa