VECTREX WITH DESPERATION

[Desperado]

Pin 3 should be -13 Volts.

So you have committed the cardinal sin and not checked all of power supply rails to start with as I have asked you to do...

Back to the power supply to find out where the -13 Volts has gone to...

Dave

Can i check this voltage on connector?

 

[daver2]

Yes...

Dave

 

[Desperado]

I checked the connector that starts from the power board and reaches the logic board....the -13V is missing!

 

[daver2]

That's what I said...

So, there are some capacitors and diodes on the power board that generate the -13V supply.

I am out flying at the moment (radio control models). So let's continue our search tomorrow. I will send you a list of things to check...

Dave

 

[daver2]

On second thoughts...

Can you check the DC voltage across the following components with your multimeter please:

D107.
C121.
C122.

Dave

 

[Desperado]

D107.
C121.
C122.

I ll check these tomorrow because power board is difficult to measure now... i need to disassemble from case
Thanks so much!

 

[daver2]

No problem.

Have a good night.

Look for signs of damage to the surrounding components when you have disassembled the power board.

Dave

 

[Desperado]

D107: -23 mV
C121: 16 mV
C122: 16 mV

 

[daver2]

Nothing getting to D107 then (or D107 is short circuit).

With your multimeter set to read AC Volts, can you measure the voltage from 0V/GND to the positive end of capacitor C120 please.

Let's see if there is some voltage coming from the transformer!

Dave

 

[Desperado]

Nothing getting to D107 then (or D107 is short circuit).

With your multimeter set to read AC Volts, can you measure the voltage from 0V/GND to the positive end of capacitor C120 please.

Let's see if there is some voltage coming from the transformer!

Dave

I am desperate!
if i put multimeter black probe on gnd i read 4,5 Vac....
with black on gnd and red probe on C120 positive leg, i read 0,02 Vac

 

[daver2]

I would be interested in the results if you take the same measurement with your multimeter set to DC Voltage. Probes both way around.

Dave

 

[Desperado]

if i put multimeter black probe on gnd i read 0 VDc....
with black on gnd and red probe on C120 positive leg, i read 0,24 VDc

 

[daver2]

Where are you getting your 0V/GND reference from?

Dave

 

[Desperado]

Where are you getting your 0V/GND reference from?

Dave

On gnd wire solded on power board Dave

 

[daver2]

I would suggest removing capacitor C120 (noting the polarity for later insertion). Either that or removing one of the leads of capacitor C120 from the PCB.

Then (using your multimeter set to AC voltage again) - measure the voltage between 0V/GND and where the positive lead of C120 should have been on the PCB.

By removing C120, we disconnect the voltage doubler circuitry (producing the -13V) from the transformer winding feeding the circuit.

Again, measure the voltage with your multimeter probes both ways round.

 

[daver2]

I assume your C120 is a 47uF 16V aluminium electrolytic?

Let's make sure we have the correct component shall we...

Dave

 

[Desperado]

I assume your C120 is a 47uF 16V aluminium electrolytic?

Yes, correct!

I have same situation also with C120 disconnected!

 

[daver2]

Can you remind me what voltages you read please with the capacitor removed.

Dave

 

[Desperado]

Can you remind me what voltages you read please with the capacitor removed.

Dave

0,25 V but without C120 i can 't hear the Diagnostic Cart Sound but i hear the sound of integrated game

 

[daver2]

Can you confirm EXACTLY which revision of tye Vectrex you actually have please.

C120 should not affect anything (especially if the -13V is dead).

Dave