Commodore 1084ST

L

limited skills bloke

Newbie
Credits
1CR
Hi there, I have a Commodore 1084ST with I suspect a power supply fault. I got it a while back, totally dead. I replaced a blown fuse, a dead mosfet on the power supply, and a shorted TDA4605 controller. That got me a pulsing green power LED, but nothing at the LOPT. The line output transistor tests ok, but a bulb wired to B+ and ground doesn't illuminate. And the mosfet just blew again.

I have some limited electronics experience and have repaired things before, but I cannot find a circuit diagram for this monitor (it isn't a 1084S, it seems to have been manufactured by Likom in the early 90s). The example circuits for TDA4065 controllers look vaguely similar, but without a circuit diagram for this set, to see what might be damaging the PSU, I'm lost. I don't want to risk further damage.

I contacted Arcade Club in Bury and they sent me here, I understand a user called @gunblade who might be local to Bury who may be able to help? I don't want a freebie, happy to pay whatever.
 
M

Mc-Q

Active member
Credits
1,450CR
there is an inductor between the B+ rail and the line-output transformer
lift it and connect a 60w 240v light bulb across the B+ capacitor
if it runs stable you have a problem in the horizontal drive or the transformer is bad.
which 1084 is this btw, the rebadged philips 8833-II or the boxy older one?

btw
 
M

Mc-Q

Active member
Credits
1,450CR
interesting - never seen that one before!
you would need some experience to fault-find it, and maybe some obscure test gear like a "ringer"
 
1

1980s_john

Newbie
Credits
6CR
limited skills bloke said:
Hi there, I have a Commodore 1084ST with I suspect a power supply fault. I got it a while back, totally dead. I replaced a blown fuse, a dead mosfet on the power supply, and a shorted TDA4605 controller. That got me a pulsing green power LED, but nothing at the LOPT. The line output transistor tests ok, but a bulb wired to B+ and ground doesn't illuminate. And the mosfet just blew again.

I have some limited electronics experience and have repaired things before, but I cannot find a circuit diagram for this monitor (it isn't a 1084S, it seems to have been manufactured by Likom in the early 90s). The example circuits for TDA4065 controllers look vaguely similar, but without a circuit diagram for this set, to see what might be damaging the PSU, I'm lost. I don't want to risk further damage.
Click to expand...
Hi,
I've not seen a Likom made Commodore monitor before, does seem a lot less common than the Philips one I have. Electrolytic capacitors are a good place to start, do you have an LCR meter to check them with? I start by writing donwn a list of fitted caps and values (I assume the PCB has labelled the components - if not take a photo and make up your own numbers), then measure each one in circuit for capacitance and series resistance, reject those that are more than say 20% below spec. Also reject any that have bulged or leaked onto the PCB. Replace with new caps and power up.
HTH,
John
 
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