naujoks

I've searched for LM7812s, but they are difficult to come by. I only found one seller in Italy. Since I've now had 3 different L7812CVs in the drive and none of them worked, I would have thought that this problem is better known an documented. Are you all successfully using L7812CVs? Is there any more detailed info how to lubricate the parts you mentioned?

Haha just no! I just put in the 7815 out of boredom, but it's actually putting out 15v in the drive, so that's no good. I'll waaaait.... 😔

I just tested a 7815, with 15v/1A from the PSU, and it outputs exactly 12V! Haha! Shall I just take it?

Looks like the whole lot is junk. I'm getting around 3v out of them. For giggles I took a 7810 and connected it, and that gave me a reading of around 10v. How can that be possible? Ten 7812, all garbage. Ordered a new pack. The saga continues. Tomorrow.

Let me try to get this right: + of the PSU to input of 7812 - of the PSU to middle pin of 7812 (ground) Middle pin of 7812 also connected to heatsink of 1050 (does it need to be connected to its PSU?) One contact of the bulb connected to the output pin of 7812 The other contact of the bulb connected to middle pin of 7812 (or heatsink).

I don't think that's right. The output pin of the 7812 is the third leg (looking at it from the front). The middle leg is ground and that is also connected to the metal part on the back of the IC. The back is supposed to make contact with the heatsink (unlike the TIP110, which is to be insulated). The output has no conductivity with the heatsink.

So the new L7812CV arrived... but it still doesn't work! Like, WTF? I could try the other 4 I have received, but considered that I've tried 5 news ones before I somehow don't think it will make a difference. The latest batch I've tried is from a different manufacturer than before. I also used the metal screw and washer to secure it to the heatsink. Ideas?

Guilty as charged, it was an El Cheapo kit from China off Alibaba.

Well, you didn't ask! 😁 I just got it recently and it's still waiting for its first use. That would have been it. I already chucked the old 7812s, and I can't be bothered to go through my garbage to pick them out again. I do have quite a few tools, even though I don't always know how to use them, but I'm still learning, this is just a hobby.

I actually have a lab power supply, which I could use to test this. The other interesting thing is that I received the 1050 with the original 7812 being replaced by a modern component, and that wasn't working either. I need to find out if using a metal screw to secure the 7812 to the heat sink has anything to do with it. For the repair I used the known working 7812 and the metal screw, to replace the plastic screw and nut that the previous owner had put it. New 7812s arriving tomorrow, so we'll see.

Oh yes, amazing! By the way, is there a way to test voltage regulators out of circuit? At least the ones I had didn't measure any shorts between any of the legs.

Yes, absolutely! Crazy to think that the only faulty part actually was a modern one, all 80s components were absolutely fine. I just put all 4 7812s that I had in my kit in, and every single one is a dud. And so was the one that the previous owner had put it. That's an almost unbelievable amount of bad luck. Anyway, thank you very much for all your help, and also everybody else who chimed in.

I've just taken the Q8 from my working drive and put it in the faulty one, and it's WORKING! The new part I was using was a L7812CV. Is that not an adequate replacement then?

Sorry to be unclear. So bulb sits between output Q8 and ground (heatsink), voltmeter is between output Q8 and ground (heatsink), showing ca. 1.7V.

I've connected the 12v/10w bulb now, but the results confuse me. It's connected between the output of Q8 and the heatsink. I'm getting only a very faint glow when switching on the drive. Measuring the voltage between the output of Q8 and the bulb I'm getting 1.8v, which slowly goes down to 1.5v. Putting the ammeter in between Q8 and the bulb gives me a reading of 0.3A.

I see. 10w bulb is arriving tomorrow.

When connecting a different load, where would the negative go? I just connected a bulb between output of Q8 and put the ground on the heatsink, but it didn't light up. It's a 35w bulb though, so maybe that's too much?

I got the MM working again. So I'm getting 0.1A idle, going up to 0.4A during motor activity.

TP14 gives 12V at the beginning and then drops to 3.8V during the power up sequence and when turning the disk lever. It goes up to 12v after a few seconds. I think my multimeter zonked out on me. I put the red lead in the A (10A fuse) socket, set the dial to A/DC (not uA or mA), connected red to the lifted output pin of Q8 and the black to TP14. When switching on the drive, I got a reading of around 0.5A, which quickly dropped to 0.1A or so but then went to 0. But now it always stays at 0. Switching the drive and MM on and off doesn't do anything. The fuse shouldn't have blown as I stayed well under 10A, but I can't check it either because the case seems glued. The MM works fine when I set it to different measurements. The drive still works as before, I checked by reconnecting the output pin. Does this give us anything to work with?

Also to say that I've measured most of the resistors (comparing their values to my working board). I'm also convinced that the stepper motor sounds less energetic than the working floppy drive, so we probably have a power drop on that side as well.

Going back to this, I've replaced most ceramic caps in the area. Haven't found a single one that's bad or even just out of spec. I now want to measure the amps but can't you tell me now exactly where I should put the meter? Between emitter of Q8 and...?

Yes.

A little over 4V.

Unfortunately I only have the one meter. But what do we actually gain from making that measurement?

If doing this shows a higher current draw than expected, what would that indicate?