Honey I blew up the mini lathe speed control board

[irving2008]

I'm guessing you meant S6006L which are Teccor 6A 600v isolated tab SCR (the 6060 is a 60A device and is definitely not in a TO220 package!) and the D6020L is a 600v 20A isolated tab diode also from Teccor. Shouldnt be too hard to work out the circuit, its going to be a full-wave half controlled bridge (2 diodes, 2 SCR arranged as a bridge rectifier) the third diode is a snubber across the motor. What other parts are there on the board?

[HankMcSpank]

Hi Irving - tks for the clarification!

Have you any schematic links for the full wave controlled bridge you mention? I'm hopeful there's nothing majorly wrong here, as there's no 'toast' or anything melted (whereas, the original board I spoke of when I bought was absolutely nuked!)

Ok, the board was riveted to that metal surround (as were those SCRs and diodes for heatsinking)- drilled the rivets out - alas, a good few components underneath. I have my first 'lead' though. There's a small 78L08 regulator on the top side of the board ....it is *very* hot (you can see it in the photo I posted aboe - to the left of the piccie next to R33). The DC voltage on its input pin is near 10V...output pin is just 2V! It could be something on it's output dragging the voltage down (hence it getting hot) down so I'll remove it from circuit & see if it checks out. Alas I don't have an 8V regulator handy if it is this ......just 20p from Farnell (but minimum order of £20!)



(a couple of LM324s and one LM339 you see there)

Edit: Ok, i whipped thAT 78L08 out - boshed it into a breadboard that I already have in place with a 16V unregulated DC as an input- it literally smoked! (which suggests it was flakey as a 16V input it should be able to handle - http://www.datasheetcatalog.org/data...INGS/78L08.pdf ). Ok, so I'll need to source a replacement now!

[irving2008]

Hank,

I order a lot from Farnell and need to put an order in this week, so I'll get you a couple - PM me your address and let me know if there's anything else you need. I thought I had one here but I can't find it.

So you have a quad comparater, probably for zero crossing detection, and a pair of quad opamps, probably acting as buffers for RC timing networks to give start up and stop acceleration/deceleration control. I am guessing the transformer is to provide some power to these and a source of isolated AC for the zero crossing detection, wonder how they drive the SCR gates. All the circuitry is operating relative to one side of the motor and floating relative to supply, unless theres a pulse transformer or opto-isolator on there and I dont see it... so be very careful when putting fingers near there...

The picture shows an ouitline of the circuit - there are several ways to do this but it should help sketch out the main arrangement...