Kurzweil PC3 - 78T05 5V 3A regulator

[nisios]

Hi everyone.

I have this keyboard in for repair.

The main 5V rail is gone, the regulator is dead.

The thing is that it uses a 3A KA78T05 regulator wich is obsolete, attached to a relatively big heatsink. I cant find it easily anymore and most of all, i wonder why those got discontinued.....
Is it a bad IC design? Too much temperature for that pakage (TO220) ?

Is there any chance this guys from Kurszweil were using these only because they had a bnunch at that time of manufacture, but they could have gone with a more standard 1.5A regulator? I'm inclined not to think so, but maybe someone might have some info on this.

I only found the service manual for the PC2, similar but not the same thing.

Maybe ill just solder a standard 7805 in place and measure the current consumption.....just being a bit lazy asking....i guess.

Thanks

[km6xz]

If the original 78T05 was getting hot, a 7805 would burn up quickly since the T version handles more than twice the current. The "T" version was made by more than one company, try searching for the MC78T05 instead of the Fairchild version.
There are a number of more modern LDO 3amp regulators but not in TO220 case. If it was getting too hot, check for high input voltage which will cause excess heat in a circuit that otherwise works properly. Most modern higher current regulators are SMD style that bonds the tab to the ground plane as heatsink. Nowadays, a switching regulator would be used which would be much more efficient and not require much heat sink.

[nisios]

But I dont know it was getting too hot in the first place. Tahts also my first thought but the fact that this regulator got discontinued made me think that maybe it had issues.

Anyway, its hard to find any these days, KA, MC, etc.

The maximum you can find nowadays i think is like 2.2 amps in a 7805 to220. I will try to get one of those and monitor the current and temperature.

[g1]

LD1085v50 is 5V, 3A, TO-220

[Enzo]

Hi nisios.

Stan put his finger on it, the part is obsolete because it is obsolete. Other parts have come out since that one, modern switching regulators are more versatile, more efficient. Engineers will design the newer parts into the models.

The TO220 can dissipate plenty of heat, but only if it is heat sinked properly. It isn't the part's fault if someone makes a weak design that doesn;t provide that. it isn't a "bad design." When a part no longer sells, no longer has a market, they will stop making it.

Is there any chance this guys from Kurzweil were using these only because they had a bnunch at that time of manufacture

No. This is a common enough myth: company X made some model with left over parts... Doesn;t happen. Kurzweil is not three guys sitting around a shop building stuff. it is a large company, and the engineers design the models to use appropriate parts. They will not knowingly use a part that is going to go out of production.

[g1]

For Portugal:
Invalid Request

[doctor]

Be attentive: recommended the LD1085 regulator has pin arrangement different from the 7805.

[nisios]

Yes, thanks for noticing. That would make it a little too bodgy, would´t do that on a clients synth.

I managed to find some KA78T05 at a local old school electronics store. we have lots of those stores here (only those stores actually). You find some really nice gems, but forget any smd stuff or anything post 90's. Nice price too. I bought the last 4.

Thanks very much guys, i see there is a very nice community here, very helpfull i hope i get to contribute.

[g1]

Be attentive: recommended the LD1085 regulator has pin arrangement different from the 7805.

Thanks Doctor, I was just looking for something that met the specs.
If the part was unavailable and it was a choice between running wires to the board or scrapping the unit, then I think such a "bodge" (or kludge ) would be an acceptable choice.
It seems a little ridiculous that they would not use the standard pin-out which would not only allow retrofit, but also upgrade from 1A or 1.5A types. (Or allow stocking one type to cover various current requirements).
Was the electronics industry in need of an alternate pin-out or does it have to do with physical structure/characteristics?