Help with dead Commodore 1802

[stj]

Re: Help with dead Commodore 1802

yes, the coil is the link from the psu stage to the tube handling.
it does not isolate the audio amplifier though.

[roadrash]

Re: Help with dead Commodore 1802

Ok i gave it one final check after solderig in the STR transistor we checked and as i was afraid of it blew the now mox resistor. Those resistors give a much bigger flash than the wire wound one's. Well that is still a bit strange because i checked all component for the psu and none were shorting. Am i right in assuming that that coil i removed is the output voltage from the psu to the monitor itself. So this rules out a monitor fault and the short is isolated to the psu circuit somewhere?

[roadrash]

Re: Help with dead Commodore 1802

You can test the output transistor with a meter, see post #44

with a meter, see post #44[/QUOTE]

Thanks. It tests ok. Ive been testing everything including the STR54041 for a short and nothing tests as a short in the power supply area of the pcb except a odd iduction coils and that new metal oxcide resistor. Should i refit the STR transistor and try power it up using the light bulb as was mentioned earlier. Ive removed L805 and connected the bulb across C812. Is there anything to check before i try this and most likely blow another resistor probably.

[R_J]

Re: Help with dead Commodore 1802

You can test the output transistor with a meter, see post #44

[roadrash]

Re: Help with dead Commodore 1802

So no short across the main capacitor?, You can also check the output transistor in the str54041 (E=pin4,C=pin3,B=pin2) however I suspect that if the str was bad it should have blown R805 (0.27Ω)

No short across main cap. Took out str54041 so how do i test this thing. My component tester only has 3 test leads. Can it be done with a multimeter? Here isna picture of what i removed there is not any room to get into it much.

[R_J]

Re: Help with dead Commodore 1802

How many resistors do you have?, Use a metal oxide one and save the last wire wound. Use a incandescent lamp in series with the ac line untill you locate the problem.

[roadrash]

Re: Help with dead Commodore 1802

Can i use these metal oxide resistors if i blow my last wire wound one?

[R_J]

Re: Help with dead Commodore 1802

It's the large one in the power supply C803

[roadrash]

Re: Help with dead Commodore 1802

So no short across the main capacitor?, You can also check the output transistor in the str54041 (E=pin4,C=pin3,B=pin2) however I suspect that if the str was bad it should have blown R805 (0.27Ω)

Just to make sure what is the number of the main capacitor?

[roadrash]

Re: Help with dead Commodore 1802

8

no, it's supposed to be 0.27ohms

desolder coil L805, connect a 40w mains bulb to the pins of C812 and try it again.
then your only running the psu and the audio amp - not the rest of the circuit.
you need the light because the psu expects a load.

I will give this a go as i went and got some old 40w bulbs.
On my last 3.3uf resistor here so dont reallywant to blow it up too. Ive had some mox type 3.3uf resistors turn up but can i use them?.

[R_J]

Re: Help with dead Commodore 1802

So no short across the main capacitor?, You can also check the output transistor in the str54041 (E=pin4,C=pin3,B=pin2) however I suspect that if the str was bad it should have blown R805 (0.27Ω)

[stj]

Re: Help with dead Commodore 1802

no, it's supposed to be 0.27ohms

desolder coil L805, connect a 40w mains bulb to the pins of C812 and try it again.
then your only running the psu and the audio amp - not the rest of the circuit.
you need the light because the psu expects a load.

[roadrash]

Re: Help with dead Commodore 1802

It blew the 3.3Ω 10 watt resistor! but not the fuse? Ok check the 4 power supply diodes, then check the resistance across the main capacitor. You must have a dead short somewhere in the primary circuit
Post a picture of that new resistor that blew open

R505 shows as a dead short. Would this be the culprit?
All others like 4 diodes are ok

[stj]

Re: Help with dead Commodore 1802

i have never seen as resistor fail without help.
a 40w lamp bulb in series with the monitor is a good idea to limit the current.
and leave the degausing coil unplugged - it's the thing that causes the bong sound - and causes a big surge.
it's around the outer edge of the front of the tube, and runs to a 2pin connector near the mains input.

[roadrash]

Re: Help with dead Commodore 1802

R801 is probably metal oxide, not wirewound.
a wirewound will get glowy hot instead of going open-circuit.
smash the old one to check the insides.

so now you need to see what made it burn!

Hhahhaha yep You said it! Do you still think it a MOX because I did order a couple of these wire wound ones and a MOX one that I am still waiting to arrive. I will now do like RJ said and rty and find that short. I never expected that. there was just I small flash from the new restistor and I knew straight away and yep! its was blown. Just as well I got another.

[stj]

Re: Help with dead Commodore 1802

told you!

[R_J]

Re: Help with dead Commodore 1802

It blew the 3.3Ω 10 watt resistor! but not the fuse? Ok check the 4 power supply diodes, then check the resistance across the main capacitor. You must have a dead short somewhere in the primary circuit
Post a picture of that new resistor that blew open

[roadrash]

Re: Help with dead Commodore 1802

I fitted a 3.3 ohm wire wound resistor and as soon as I powered it up it blew it again.

[roadrash]

Re: Help with dead Commodore 1802

where the fuck are you shopping?????

RS is free delivery,
germany and poland only cost about £6

That was DigiKey.

Ive got some wirewound coming from a trader on Ebay for few quid.
I will do as you said and solder in on top of the original.

[R_J]

Re: Help with dead Commodore 1802

The resistor is just to provide a bit of surge protection when you first turn it on. It is in the ac line, it can be made from anything, its not important.
I just used digikey to find a mfg. part number of the same type and mounting that you are replacing.

https://uk.farnell.com/international...10w/dp/1457934 £0.933