Attempting Intellivision repair

[JohnPCAE]

Huh. I guess the schematic is wrong. I'm curious as to what you might measure at STIC pin 20, since that's where +5.7V is going.

 

On OT note, I found some problems with my schematic when I decided to validate it by laying out a PCB. Corrected one plus PCB is attached.

Inty_II_Power_Board.zip

[mr_me]

I think that 2-pin connector is unregulated.

 

To test the transformer the service manual has the following. Disconnect the transformer from the power supply pcb.

Pins 1 and 3: between 7.6 and 9.4 vac rms

Pind 2 and 3: between 7.6 and 9.4 vac rms

Pins 4 and 5: between 15.3 and 18.7 vac rms

[SiberianSpForces]

AC tested the transformer;

Y & B - 17.5

G/Y & G/G - both are 9.1

G & G - 18.6

 

Swapped out the remaining socket chips too. The logic board looks great. No burns or bloated caps. Now when I reset, colored lines flash.

Edited May 7, 2017 by SiberianSpForces

[SignGuy81]

I think that 2-pin connector is unregulated.

 

To test the transformer the service manual has the following. Disconnect the transformer from the power supply pcb.

Pins 1 and 3: between 7.6 and 9.4 vac rms

Pind 2 and 3: between 7.6 and 9.4 vac rms

Pins 4 and 5: between 15.3 and 18.7 vac rms

That is correct, I just looked at the schematic as well. If he were to check it while wire was plugged in it would probably read around 5.6V as it said. The excess voltage from the unregulated supply would be dropping across the 12ohm 2 watt resistor. But since checking it open with a multimeter which has high impedance it is going to read higher voltage than stated in the schematic since it is unregulated supply and it hasn't got a load on it.

[HunterZero]

Yeah the 2 pin supply is unregulated. The STIC datasheet says it takes 5.25V at pin 20 so 5.6V on the schematic is probably correct under load. It's a convoluted power supply setup to be sure.

 

So back to the 16V unreg supply...

 

Did you check the 2200uF 25V cap? What voltage are you getting on the +ve lead of that cap? Worth checking the rectifier diodes CR5 thru 8, and regular caps C9 thru C11 (C11 is nearest the large 10000uF cap).

 

I usually replace the two large electrolytics on the power supply board (and the two regulators) with new ones anyway.

[HunterZero]

On the main board - Check for voltages at pins 34 (5V), pin 35 (-3V) and pin 36 (12V) of the cpu.

 

If you have a probe, check for clock at pin 15 of the STIC, and that STIC pin 13 is pulsing and has continuity to pin 2 on the CPU1610. We can then check the CPU is actually running.

 

The CPU1610 data lines are on pins 6 to 21.

[SignGuy81]

It's the original. Here's what I got from the power supply board;

2 pin/blue wire - 12.68

 

 

Was this with the wire plugged in while checking?

[HunterZero]

And it's suspicious that C11 blew on the PS board, and the unregulated voltage is below what it should be with no load. C11 is part of the unreg 16V supply. I suspect the CPU isn't getting all the voltages it needs through the circuit with the 2 2N3906 transistors Q1 and Q2, and isn't starting. These transistors generate a pulse for the CPU at pins 37 and 38.

 

So the recommendation stands to check the 2200uF cap, and the rectifier diodes CR5 thru 8, and regular caps C9 thru C11 (C11 is nearest the large 10000uF cap). Then move to checking the logic board around Q1 and Q2.

 

That you are getting a black screen indicates the RF circuit is good, and that there is a flash when you press reset indicates that the STIC is probably good too - at least good enough to boot the system.

 

- J

[SiberianSpForces]

And it's suspicious that C11 blew on the PS board, and the unregulated voltage is below what it should be with no load.

I swapped transformers and that's when the C11 blew. Now I got another PS hooked up.

 

Was this with the wire plugged in while checking?

Unplugged.