Help with dead Commodore 1802

[roadrash]

I wonder could someone help me get my old Commodore 1802 monitor working again. This was working perfectlyfor years andthe other day I left it running for a few hours and when I came back it was dead. Ive checked fuses but they are ok so must me a PSU fault.
There is 240v AC getting into the PCB and I can follow it quite a distance. Visualy looks like nothing is wrong but there is a STR54041 regulator which ive ordered just in case its that.
I have found and attached a Schematic and i have a service manual but its for the 110v NTSC version.
thank you

[R_J]

Re: Help with dead Commodore 1802

It might be a simple as one of the two small caps in the primary, 2.2µf or the 10µf
Are you getting any voltage on the secondary of the power supply?
Check Q402 horizontal output transistor and see if it is ok and not shorted. If it's ok its likley just the power supply at fault

[roadrash]

Re: Help with dead Commodore 1802

Thank you RJ,l. I have had a few sucesses recently and it would be nice to sort this one seeing as its posibly something minor causing it. Ive taken some pictures for you so can you point out these 2 caps in the primary to me..Can you point out the Secondary section.
I really do need to be able to identify these areas now that I am doing so many PSU's now.

[budm]

Re: Help with dead Commodore 1802

May be you should also upload the service manual.

[roadrash]

Re: Help with dead Commodore 1802

The transistor Q402 shows a short between the base and emitter when its in circuit. Should I remove it to check it or is this enough? Plea Here is the service manual but remeber this is for a NTSC model and mine is a PAL model. se point out where the primary area is..

[R_J]

Re: Help with dead Commodore 1802

Q402 short between base & emitter is normal, you are measuring the horz. drive transformer, no short between e - c is good, The transistor is likely ok.
Start by check in for voltage on the main filter cap. C803, then do you have voltage on pins 4 & 5 of the power supply transformer

The cap I thould could give no start of the power supply would be C806 and maybe C825. Have you checked the board for poor solder connections? Parts like large resistors get hot and over time the solder goes to hell, transformer pin connections also get weak overtime.
Are you getting any voltages from the power supply?
The primary side is anything within the white line where the power cord connects to the board

[stj]

Re: Help with dead Commodore 1802

i would isolate the line output transistor and then see if you have B+ as it should be.

if this is a philips design then it may have a shorted line-output transformer.

[Agent24]

Re: Help with dead Commodore 1802

With something that old, don't forget about cracked solder joints.

[roadrash]

Re: Help with dead Commodore 1802

Q402 short between base & emitter is normal, you are measuring the horz. drive transformer, no short between e - c is good, The transistor is likely ok.
Start by check in for voltage on the main filter cap. C803, then do you have voltage on pins 4 & 5 of the power supply transformer

The cap I thould could give no start of the power supply would be C806 and maybe C825. Have you checked the board for poor solder connections? Parts like large resistors get hot and over time the solder goes to hell, transformer pin connections also get weak overtime.
Are you getting any voltages from the power supply?
The primary side is anything within the white line where the power cord connects to the board

Checked all you said RJ and everything is OK and those 2 caps are within tolerence. Ice also resoldered many contacts especially around things like the LOPT etc. I cant see any bad looking joints and those that look a bit dull I have resoldered. There is quite a bit of flux on this board but the joints look good.

[roadrash]

Re: Help with dead Commodore 1802

i would isolate the line output transistor and then see if you have B+ as it should be.

if this is a philips design then it may have a shorted line-output transformer.

Sorry STJ can you put this in simple talk. How to isolate LOPT and what should B+ be doing? It is a Daewoo CM-120 made for Commodore.

[Agent24]

Re: Help with dead Commodore 1802

B+ looks like that 121v rail which should be on, if I read it right, C813. 100uF 150v looks like.

[roadrash]

Re: Help with dead Commodore 1802

Checked c813 but i think you meant C814 cos 813 was a ceramic. It looks like a lot of caps are leaking but its just adhesive. I still dont understand what STJ meant about isolating the LOPT and check B+. How do i isolate the LOPT and where is B+ and what am i checking it for?

[R_J]

Re: Help with dead Commodore 1802

post#2

Are you getting any voltage on the secondary of the power supply?

post#6

Are you getting any voltages from the power supply? Start by check in for voltage on the main filter cap. C803, then do you have voltage on pins 4 & 5 of the power supply transformer

I will guess you are not getting any voltages even on the main cap, so it is either R801? 3.3Ω 10 watt resistor is open or the power switch is bad

[stj]

Re: Help with dead Commodore 1802

@roadrash.
get a lamp holder and a REAL 40w lamp.
poundland should have them.

then i'll explain how to isolate the power section from the HV/deflection and test the psu on it's own.

[roadrash]

Re: Help with dead Commodore 1802

RJ there is voltage at the filter cap and on pins 4 & 5 of the LOPT. No voltage anywhere else like 12v or 5v. I can only get 240v AC.

[R_J]

Re: Help with dead Commodore 1802

I think I read the pins wrong on the transformer, It should have been pins 4 & 2 (the primary winding) Do you get any other voltages on the str54041 Pins 1, 2 and 4 ?
You could also check those resistors in that primary circuit, maybe one of them is open.

[stj]

Re: Help with dead Commodore 1802

the lopt is the one with the big red wire to the crt.
all voltages on it are high frequency ac so you didnt meter it - and you shouldnt try.

[roadrash]

Re: Help with dead Commodore 1802

I think I read the pins wrong on the transformer, It should have been pins 4 & 2 (the primary winding) Do you get any other voltages on the str54041 Pins 1, 2 and 4 ?
You could also check those resistors in that primary circuit, maybe one of them is open.

sorry I had to go away for a while and I was waiting for a new Q402 2SD1397 Transistor to arrive after I thought we had established it might have been faulty but I cant find here now for some reason. Anyway I soldered in the new transistor and I couldnt get the monitor to power up at all and there was no 240vAV bgoing in. Ironically it was the latching on/off switch decided to fail just at that moment. Ive jumped the connections so now have 240vAC going in again and just want to check that I am now looking for voltage on pins 1 & 2 of the LOPT is that AC or DC volts?

[R_J]

Re: Help with dead Commodore 1802

I just asked to check Q402 to see if it was shorted, you checked it and measured a short between b-e which is normal, you were measuring the horizontal drive transformer secondary. I assumed there was no short e-c since you did'nt say.
There are two (2) secondary voltages produced by the power supply.
One is 12 volts from D807, the other is the B+ 121 volts from D806
Check if they are there or not.
Pin 3 of T461 (horizontal output transformer) will have B+ 121VDC, Caution measuring pin 1, it will have ~120 VDC, BUT if the horizontal circuit is working it will also have 1~1.5KV of 15khz AC

[roadrash]

Re: Help with dead Commodore 1802

I cant get any voltage from D807 or D806. Thats using both AC & DC and connecting black proble to a heatsink which should be a good ground. Or should I have reversed the probes as well with it being on a diode.Something interesting when I powered it up this time It made a slight bong noise and and you could hear it power up. Dont remember if it was doing that before.