Testing a Printed circuit Board

[unclejed613]

that should work....

[sheldonstv]

that device should be fine to use but you need to make sure the device pin outs are identical with the original device you are using as a replacement and if the device is attatched to a heatsink ,and that heatsink is earthed on the pcb you need to mount it with insulating hardware so the metal tab is isolated from the heatsink (if it is grounded at all)otherwise there may be a loud bang on switch on.......let us know how you get on

[ke1000]

Hello

Thanks for the replies. Last day away today, for a while. Should be able to spend some time repairing the mill from tomorrow.

Off now onto the M62

Regards

Bruce Davis

[ke1000]

Hello All

Well it couldn't go smoothly, could it? I had a nice ride to my local Maplins Friday, only to discover that contrary to what was said on the website, they didn't have the diodes or triac in stock. However they did tell me that the triac is a BTB16 600 BW. Mouser want £12 delivery for the items that cost £2 and weigh nothing, seemed a bit excessive. So I went on the Maplin site they didn't have a BTB but they had a BTA and assured me it would fit, so I ordered it, as they only charge £3 P&P.

I hope they arrive tomorrow, as I am away at Stafford from Friday.

Regards

Bruce Davis

[#1supertech]

WOW -

Had no idea you were in England of all places. I guess this site here takes posts from all the world as it were!

I couldn't help but add in some of my expert repair advice here, as I've repaired a few treadmills (TM's) in my time, and most were a bit more complicated then the SIMPLE PCB motor control you are showing in your post. I guess at roughly $1100 for that Mill you have there - the mfr in Austria wouldn't just swap out the boards huh? Guess not! Either that or it's a cheaper model with a only a few basic bells and whistles - as by the small footprint PCB design and all?

First of all - some basic sound soldering/desoldering advice is needed here.

NEVER USE copper desoldering braid if you can help it! It only helps to ruin the PCB copper runs when too much heat is constantly applied to the solder point to be worked on. Buy an inexpensive but quality type plunger desoldering tool if you can. They are under $10 and well worth the money! Practice on some bad throwaway boards first to become a desoldering Pro first, and then apply it to the good boards! You will appreciate the ease at which the solder now comes off the board, but never damages fragile PCB's. That or if you must use that copper braid then use a liquid acid flux first - on the spot to be desoldered - such as a #30 by Superior Flux & Mfg Co. Solder will now flow off the spot much quicker, and with less damaging pressure effects from the soldering iron TIP force being applied, and will also help reduce the overall heat damaging effects greatly.

Same goes for a good soldering station as well. My station of choice was/is a Weller model TC-202 (WTCPN series) base unit using a TC-201 pencil assy with Zero Tip Voltage Isolation and automatic temp controlled tip system that uses preset soldering tips according to their size (wattage or heat delivered) and use.

Even though the unit's rated output wattage might be stated at 60 watts that doesn't mean that is what is at the TIP point in so far as for heat wattage delivered. Bigger TIPS produce more wattage in the form of point area and heat. Smaller TIPS just the opposite. If I want more Tip Heat for doing bigger desoldering areas where I have to stay in contact a bit longer then I use a bigger Tip. Where delicate work is involved I use a smaller Tip.

I also don't need the fancy digital displays and extra bells and whistles with more expensive units, as I consider myself a Pro when it comes to component level repair! I learned from the BEST starting out in my Electronics Degreed field and then some!

As for your posted PCB there - sure is a small control board in that shop Mill.

Most jogging/running TM's that I've worked on have 2 bigger PCB's minimum in the belt drive "motor compartment". One is the CPU Logic Brd, and the other usually being the Drive Brd. Of course you don't have a TM, so that goes without reason. Your shop Mill there looks to be a fairly simple piece of work equipment in this case.

In checking the PCB components whether they are diodes, resistors, or just basic diode junction transistors ALWAYS USE a good quality DVM to perform those tests (or a cap testing meter), and NOT by using an older analog type multi-meter - such as what I believe you are using unless I'm guessing wrong here? I just don't trust the older analog meters anymore - those that I too grew up with when I first started out eons ago now!

In troubleshooting (T/S) your (any) PCB there - always desolder only 1 lead from any axial 2-lead passive component (unless it's a multi-pin/lead passive device package then remove it entirely). Where the component IS a typical 3-pin active device transistor, SCR, TRIAC, or say (MOS)FET in nature - then definitely desolder the related part totally - even if it's heatsinked to the PCB, as otherwise you will never DVM check it out properly. Unless you definitely KNOW that the latter is true then there's no need to remove it (ie: burnt or cracked casing, etc).

I've had to do the latter with higher priced TM's even though the related Power Resistors on the PWM motor drive boards were at fault to begin with. Just because a high wattage SURGE resistor "looks good" on the outside doesn’t mean it "IS GOOD" inside. I've seen them go out of spec by as much as 50-60% of rated value and tolerance, and even partially OPEN UP when superheated - or act as an OPEN in the SURGE or feedback circuit - thus sending the control board into shutdown!!

Rarely will a 3/4 turn or single turn TRIM POT go bad unless it's a cheaply made variety to start with. I've seen the ones like you have there - on your PCB - have wiper intermittents - as from contact age, but it's rare. Always look for the obvious first!

Tapping the side of the POT slightly while measuring it should show no signs of value wander! If it jumps then its SHOT - replace it. Try and measure its "set point" out of circuit first, and replace it with a 10-turn POT instead - so a more accurate setting can be made after the R&R.

Which makes me wonder about what you said in your original post about the shop Mill making a "bang" and then it just stopped working?? That sounds more like a startup CAP blowing out - in regards to the "bang" you mentioned, unless that was indeed a purely mechanical bang you heard?

Are you sure the motor doesn't have a "soft start" CAP feature added to that drive motor mounted somewhere? Some shop routers use a "solid state" PCB soft start feature, and use a specially wound "Y" motor as well - one with a special "Y" startup winding added so that it retards a fast ramp up in speed current, but their PCB design usually has a weak IC controller chip on it - that when it fails nothing works at all. That chip being all but "proprietary" in nature is all but harder then hell to find should it (the IC chip) ever go bad - as I once found out fixing a 3hp model. I wound up just bypassing (gutting out) the controller board altogether, and just made it a single speed router. With an added $12-13 aftermarket external speed controller I bought from Harbor Freight Tools at 1/2 price on sale it worked just fine as a permanently mounted - fully speed controlled - bench router!

Anyway -

In your case - your PCB there doesn't show any outward signs of component failure at all, but to have all the bridge diodes go bad (as you say) tells me there is more going on there then just the PCB as it were. Btw - that TRIAC is just epoxyed in place so as to help prevent micro-arching should the soldered leads come loose from any excessive vibration, as I'm guessing there is when running under load. Do you have a lot of hours on the Mill? Have you also checked the DC motor brushes? Maybe the DC motor brushes are near their end life if there are high hours on the Mill? Have you ever checked them out as well?

As far as for finding electronic component parts online - I would stay away from Mouser and Digi-Key as they are a big rip off to start with - as related to their ridiculous parts price markups and all (making their real profit killing on the shipment part as you too have somewhat stated). Newark isn't too bad I would guess - although I have never had to order any electronic parts online, and then have to deal with the shipping part as well. I have tons of electronic parts outlets all around me where I live! I would maybe try NTE parts replacement if they can cross-reference that original part you have there to start with. Otherwise their direct NTE replacement part for that Q6004L4 is an NTE5645.

Hope this helps out. Let us all know OK?

Frank

[ke5frf]

I was just about to make the point that Frank has made here.
I didn't notice in this thread if anyone admonished you to check the diodes, triac, and resistor resistance by lifting leads off the board. I noticed you gave diode ohmic measurements and said the diodes read "000" either way. Well, even in circuit this shouldn't be the case but I never trust "in circuit" resistance readings. Been burned too many times by overlooked parallel components!

Honesly, the best way to troubleshoot a circuit like this is on an AC voltmeter point-to-point with voltage applied but I understand if you aren't familiar with electronics that this wouldn't be the time to start learning

Just a hint if you are willing to try measuring the operation of the circuit with power applied, if there is an open circuit, chances are you will read the full AC supply voltage dropped across the faulty component. That would be the voltage at your wall outlet unless there is an external transformer somewhere that we aren't aware of. And all of this assuming the reverse-engineered schematic that someone posted was correct.

[ke5frf]

I have a hard time believing all of the bridge diodes are shorted. If these were read in circuit, and the motor leads were still connected the the motor, I'm suspicious that you may have been reading the motor windings some sort of way instead of the diodes. Just a hunch. I don't think I have ever tested a motor circuit with the rectifier right before the motor like that, but I have with a transformer secondary which is basically the same thing when the circuit is deengergized.

[ke1000]

Hello All

Thank you fro the latest answers I can see now how Little I know and yes I live in the North West of England in Southport about 15 miles north of LIverpool. The Mill is the Proxxon MF70 and yes it's really small, a table top size. Since my last post I have desoldered all the mains voltage cables from the board, i.e, neutral, negative to the motor, positive to the motor and the supply from the isolating switch, so that I could remove the board from the mill to make is easier to remove the diodes. I found out like you said that the desolder braid is hard to use only being able to get the solder up the first 1/16 of an inch. I have phptographed and sketched everythng, which is why it has taken so long. I have been unable to remove the diodes as at first I ahd nothing small enough to hold the body and pull when I melted the solder. Now I have a pair of tweezers but although I have straightened the ends and melted the solder the first one refuses to come out of the hole.
Do you think I am in over my head and I should contact Proxxon to buy a new board?

Regards and Thanks, I will re-read the latest posts to see if I can get to understand.

Bruce Davis

[sheldonstv]

o my- it all comes down to practise when you are using desolder braid i have never had a problem with using the stuff ...........

[#1supertech]

ke1000,

I didn't get a notice that you posted a follow-up to the thread so that is why I'm replying kinda late here.

I see you have the PCB out so all you have to do is now re-measure the diodes and they should show that they are indeed all good, or at least I would think so.

No need to desolder the bridge rect diodes if the board is out of the circuit.

Forget that solder wick (braid) crap - GET A SOLDER SUCKER device either from online or at your local electronics store there near you. I'm sure you have one - right?

I'm thinking that your country has that LEAD FREE standard as well and that you have NO LEAD in your solder there??

Also - you need some solder acid flux #30 - such as that like Superior Flux Mfg Co sells. This will aid in your soldering iron tip (hopefully it's cleaned & tinned properly first) being able to flow the solder easier to start with. All solder joints have some form of surface oxidation (impurities) the older the board is, and thus make it even harder to desolder! That or it is LEAD FREE and that makes it harder as well. Here in the USA we use a 60/40 solder and it flows very easily! Hopefully your PCB there used lead in the solder (but I doubt it) otherwise that too will make it harder to desolder!

Do that diode test again, and repost an update for us.

Thx,

Frank

[#1supertech]

PS

Forgot to ask you - What kind of DVM are you using to test the diodes, etc.

What brand name and model that is??

Frank

[ke1000]

Hello

Thanks for all the help. In answer to a previous post the "bang" came from the area of the PCB and the switch. I won't desolder the diodes and will look to get a solder sucker. Up to now I have onl;y used soft solder for the wiring on Motorbikes and cars.The solder I use contains lead it is 1.6mm cored. The mill is about 5 years old made in Germany, I don't know about the solder on the PCB. The Tester I have is a Caltek CM1505. What results should I be getting, testing the diodes in situ?.

I can't always get access to the computer as my wife is doing a course and uses it for assignments and research on the internet, so please bear with me if I don't answer right away.

Regards and Thanks again

Bruce Davis

[#1supertech]

Hello Bruce,

Just read your reply, and I did a retake (relook) at not only your prior posts, and a few others including what (unclejed613) noted earlier (in #4 post) about the BURNT spot on that TRIAC, but I also reloaded the pix you posted, and it really does look like something may have shorted out the components in ? here! Esp that (TRIAC ?) as by the burn mark on the top of the heat sink mounting pad - whatever it's p/n is??

(unclejed613) posted in #4 that your PCB circuit there is similar to, or basically a dimmer circuit feeding a bridge rectifier, which then feeds the motor, and he's pretty much correct in saying that. The PCB motor control being pretty simple in design and function at that.

What probably will be harder for you to do is to desolder all the bad parts, and then successfully replace & resolder the good parts - after you find exact replacements for them.

The TRIAC (TR1), and DIAC (D5) will be the hardest to find no doubt.

I also missed that/the PDF file drawing you made and posted, so I just now got to look at that as well.

Btw - your DVM (or DMM if you like) is a pretty good model from what I noted online and the overall accuracy isn't too bad either.

Seeings you DID say the PCB is now out of the Mill, and there are NO other external connections to it - then it should now be safe to do a accurate test measurement of the components on it.

1st - To check the DIODES you just put the meter select in the DIODE test mode (read your operators manual as it will show you how to do it if you are unsure).

Then in the forward bias config you should get a reading of .600 (volts), or very close to that across each diode in test - if they are indeed good. In some cases the diodes may read a tad lower like a .525 or maybe even lower at say .475, and though they may look bad that may not be a bad diode esp if it's a higher wattage rectifier. Just depends on the Mfr and its specs! If all 4 diodes read pretty equal to each other then chances are that they are all good. If you see all 000's across any 1 diode, or all 4 in ? then you indeed have shorted out (blown) diodes there, and all 4 need to be replaced!!!

Next - Test all 4 diodes in the reverse bias mode, and you should now see only a "1" displayed on the meter across each diode being tested. If you see anything else displayed - including all 000's - then for sure all the diodes are bad as in shorted (blown out), and again - all 4 need to be replaced.

I may have spoken in haste - as to what I said earlier about them being good, as now in looking at that burnt TRIAC there - I'm no longer sure that may be the case, and that what you measured before may indeed be showing the beginning to the end of all the related diode-junctioned components being blown out!! Namely D1 thru D4 & D5 as well as TR1.

As to that TR1 there make sure you carefully remove it as well as there should be a component marking on it - regardless if the PCB Mfr took "blackout" and covered over it just to hide that part. Sometimes they do that just to get you to buy a whole new PCB from them.

If they indeed black painted over the p/n on that TR1 part try and first remove the paint (lacquer) very carefully using mild (non-acetone) finger nail polish remover first. If that doesn't work try using a razor blade flush to the surface and shave off the black paint/lacquer until you can read the p/n. If that fails to work then we can try to match the part to one that is close in SPECS. Usually (hopefully) the motor will have some ratings on it, so that will help narrow it down a bit.

The PCB shows the correct insertion (polarity or bias) of each diode, so make sure when you R&R the bad ones with new ones that you get each one right - as to it's proper junction placement - otherwise you will blow everything out once again!!

Next - In checking the resistors they will have to have at least one pin removed from the board to be measured correctly. The POT will need to be totally removed to be measured properly! If any one resistor is out of spec (including the POT) then replace the bad resistor with the same identical valued resistor AND NO OTHER!! Must be exact tolerance % replacement as well! Wattage can be a bit higher, but by looking at the pix it doesn't appear there was any prior HEAT damage to the PCB so going with the same wattage rating should be just fine!

Be careful when removing that POT - so as not to disturb the preset wiper setting position, and just measure across the 2 outside pins, as that looks like to be 500K ohm pot as by what you had on the PDF drawing? I can't see what's after the 2nd 0 as that C2 CAP is in the way on the pix you posted, but if there is a K then it's a 500,000 ohm POT. R2 should read 56K ohms 2% tolerance, and R1 should read 26K ohms 2% tolerance if I read your color bands posted right?

Once you've established that the POT is indeed good (hopefully is) then measure across the center wiper pin to either outside pin, and next mark down on a piece of paper what that value is - JUST FOR REFERENCE - in case the wiper arm setting should get disturbed. Be careful when desoldering & handling the POT so that doesn't happen!

You may also want to pick up a small pair of used surgical type locking hemostats (if you can find them used) so you can better snap onto the leads of the components when desoldering them, as they will act as not only a heatsink to protect any "good" components, but also will aid in lifting off the pin or lead of whatever you are trying to desolder as well. Tweezers are rather useless for doing this kind of repair work!

As for the 3 CAPS on the board - they too will all need to be taken out and measured for proper value. If they have been compromised - esp C2 & C3 (possibly being shorted out) then those too will have to be exactly matched up and replaced as well. I doubt C1 was hurt - as it is across the incoming AC line, but best to check it as well. Never know as it too may have shorted out as well.

TR1 & D5 will definitely need to be replaced for reasons above! No getting around that part.

Btw - that 1N6007 I was seeing on your drawing of D1 thru D4 comes up as a ZENER DIODE on Microsemi's data sheet - which seems a bit strange unless you got those numbers wrong, and they are indeed a 1N4007 instead??

Please try and double check those numbers again and post the results if different - thx!

Btw - how many hours would you guess you have on this Mill?

Lastly - Is it possible for metal shavings to get into the area where the PCB is located? As related to the TR1 part that is.

Best regards,

Frank

[ke1000]

Hello

Thanks for the replies. I have printed them off as there is a lot to take in. I will get back on tonight (my wife is at her course) with answers I hope.

Regards and Thanks

Bruce Davis

[ke1000]

Hell All

To answer a question I missed before I have used the mill for about 50 hours, but it was second hand when I got it. I have mainly used it for drilling small holes(0.5mm - 2mm) in mild steel, I am making a small traction engine called sweet sixteen.

I have read the responses and have re-tested the diodes so far. On the diode setting of the multimeter, I get 000.6 on all of them, even when I reverse the leads, which I hope is what is meant by the reverse bias test.

I have "tested" the motor using a 12V car battery charger and it turns over, albeit slowly. According to the Proxxon agent in the UK, brushes are not available. If the motor fails you buy a new one (£30+) good way to make money.

Regards and Thanks

Bruce Davis