Help with dead Commodore 1802

[R_J]

Re: Help with dead Commodore 1802

At filter cap C803 there is no AC voltage. This is correct! IT IS DC VOLTAGE!!!!

[roadrash]

Re: Help with dead Commodore 1802

At filter cap C803 there is no AC voltage. This is correct! IT IS DC VOLTAGE!!!!

Yes thats right. No voltage at filter cap. I am right measuring accros the 2 cap contacs (+and -).

[R_J]

Re: Help with dead Commodore 1802

What do you have in place of the resistor? if there is nothing there, You will not get any voltage across the capacitor because you are not getting any AC to the diodes.

[roadrash]

Re: Help with dead Commodore 1802

What do you have in place of the resistor? if there is nothing there, You will not get any voltage across the capacitor because you are not getting any AC to the diodes.

I put this bulb ain place of the resistor maybe i need a bigger bulb? It measures 72.5 ohms.

[stj]

Re: Help with dead Commodore 1802

strange, you should see some voltage and some life from the lamp.

[roadrash]

Re: Help with dead Commodore 1802

strange, you should see some voltage and some life from the lamp.

Well I just wired one of those ever ready bulbs to 240v mains and it doesnt light up. They all seem to be the same. They are nor open circuit and show a resistance but dont iluminate with 240v ac. I think these bulbs are what are fitted into ovens etc but surely they should light up. I will go andf buy some more of the bigger ceiling type bulbs tomorrow and have another go. No wonder we havent been getting anywhere.

[stj]

Re: Help with dead Commodore 1802

it's really strange that you see a resistance but no life - be interesting to do an autopsy and cut the metal cap open!

[R_J]

Re: Help with dead Commodore 1802

I just checked a couple incandescent lamps, these are 120vac 60watt = 16Ω. (Christmas light) 120vac 7 watt = 189Ω, Appliance lamp 120vac 40watt = 27Ω

[roadrash]

Re: Help with dead Commodore 1802

I just checked a couple incandescent lamps, these are 120vac 60watt = 16Ω. (Christmas light) 120vac 7 watt = 189Ω, Appliance lamp 120vac 40watt = 27Ω

You are not going to believe this but that length of 3 core flex i was using had a break in it and after i cut 6 inches of each end it now works. What are the chances of that.
I didnt think to check the cable as it looked like it was good. Anyway i now have the bulbs iluminating as they should. I will have another go at it later now to see if i can make any sense now over what we checked.

[roadrash]

Re: Help with dead Commodore 1802

I just checked a couple incandescent lamps, these are 120vac 60 watt = 16Ω. (Christmas light) 120vac 7 watt = 189Ω, Appliance lamp 120vac 40watt = 27Ω

Sorry for delay getting back to you both but was in hospital yesterday getting steroid injections into my spine and boy was I was I very sore today.

Right well got all the bulbs now working as they should and when powered on the only bulb illuminated is the one across where the resistor R801 was. The bulb where L803 was does not light up.

The voltages now are now as follows:

At filter cap C803 it fluctuates between 6.5v DC and 16v. Although when first powered on it reads 6.2v DC and slowly rises the longer its turned on.

On T801 at pin 2 the voltage fluctuates between 9.5v and 13v DC but If I set the meter to AC I get a steady 30v which makes me think its AC and not DC voltage there.
Pin 4 it again fluctuates using DC scale between 8.5 and 13v but if tested using the AC scale I get 30v.

At the pins 4 & 5 of the LOPT again the DC voltage fluctuates and its impossible to get a steady reading. If I measure it using AC scales Pin 4 still fluctuates a little buts around 13v and Pin 5 its the same slight fluctuating but up to 15v.

According to your schematic RJ I should be using the DC scale to measure these voltages. I am taking the DC ground/negative from the C803 Cap on the side of Q803 & R803 & Q805 which according to your schematic RJ is the the DC ground.

So it seems I am not getting rectified voltage or am I doing something wrong still?

[stj]

Re: Help with dead Commodore 1802

are you sure the rest of that cable is good?
you should see about 340v dc across the main filter cap

[roadrash]

Re: Help with dead Commodore 1802

are you sure the rest of that cable is good?
you should see about 340v dc across the main filter cap

Yes that cable ok now because if t wasnt the bulb that is replacing that big resistor woulnt illuminate.
That is the resistor that kep popping if you remember and is what we were trying to diagnose..
What would cause a low voltage at that filter cap?
I just tested it again and I am getting 18v DC.

[R_J]

Re: Help with dead Commodore 1802

The bulb you are using has too high a resistance, and remember that 72.5Ω you measured is the DC resistance, it is going to increase even more when it lights.
The A/C voltage is being droped from 240vac to around 13vac to supply the diodes which then outputs 18vdc.
So you need to find a regular 60~100 watt Incandescent lamp

[roadrash]

Re: Help with dead Commodore 1802

The bulb you are using has too high a resistance, and remember that 72.5Ω you measured is the DC resistance, it is going to increase even more when it lights.
The A/C voltage is being droped from 240vac to around 13vac to supply the diodes which then outputs 18vdc.
So you need to find a regular 60~100 watt Incandescent lamp

Ive connected 60w bulbs to both places now and when i power it up i hear a clicking noise and one of the bulbs flickers which then changes to a buzzing sound. Voltage at filter cap is still only 15v

[R_J]

Re: Help with dead Commodore 1802

I would just use the 60watt lamp in place of the resistor R801.

[roadrash]

Re: Help with dead Commodore 1802

I would just use the 60watt lamp in place of the resistor R801.

Ok i put the smaller bulb on L805 and when i power it up i still get the ticking noise and the 60w lamp flickering.

[stj]

Re: Help with dead Commodore 1802

what AC voltage at L802 ??
input AND output side?

[R_J]

Re: Help with dead Commodore 1802

Check if you have ANY voltage on C814 or C812, if the power supply is ticking, it is trying to start but can't, either due to a short in the secondary or the primary can't start properly. I would start by replacing C806 and C825 and see if it makes a difference.

[roadrash]

Re: Help with dead Commodore 1802

what AC voltage at L802 ??
input AND output side?

I get 237v AC.

[roadrash]

Re: Help with dead Commodore 1802

Check if you have ANY voltage on C814 or C812, if the power supply is ticking, it is trying to start but can't, either due to a short in the secondary or the primary can't start properly. I would start by replacing C806 and C825 and see if it makes a difference.

Check if you have ANY voltage on C814 or C812, if the power supply is ticking, it is trying to start but can't, either due to a short in the secondary or the primary can't start properly. I would start by replacing C806 and C825 and see if it makes a difference.

C806 & C825 when tested give the following results:

C806: c=233nf vloss=1.5% ESR=1.6 ohms
C825 c=12.25uf vloss=0.7% ESR= 3.0 ohms.

Will need to get some 10uf 160v if its no good as I only have 50v.ones.