electronics guru's

[Bibio]

good evening my fine organs

i have a few questions about resistors.

story: i have an AC motor speed control board that has seen better days and i want to refurb it.

1. does the wattage of a resistor matter in what i think they call a jacobs ladder e.g its taking in 240vac and stepping it down to 110vac using resistors?

2. as the speed control is getting on a bit i intend to replace all the resistors on the board as there is only about 40 or so. so is this wise?

3. as i intend to replace the resistors is it better to replace with what's already there which are carbon film or should i use metal film as a replacement where i can?

4. while i'm in there should i also replace the capacitors?

muchas gracias

lance

[tigersaw]

1: very much so
2: Can't do any harm, but if it cleans up, the components measure correct and the joints are sound I would not bother? Are they heat damaged?
3: That depends on the wattage - are they designed to dissipate any heat? If they are carbon film and not wire wound I'd guess it wont matter
4: Capacitors? Are they electrolytic or just surge supressors?

What is this gizmo?

[Bibio]

its a speed control board for an AC synchronous motor on a turntable (Pink Triangle LPT GTI)

it started playing funny burgers years ago so it has sat on a shelf feeling sorry for it's self. i'm interested to start spinning the black stuff again but don't want to go spending lodsa cash on a new deck. besides the LPT is rather a nice sounding deck, or it was when it worked.

there are a few resistors showing heat stress.

the capacitors are electrolytic (can style).

[21QUEST]

Hi Lance, would something like this(link below) be any good?

I'm no an electronic guru so link might be completely useless to you :p
It's just so happens I'm currently looking at using one of the DC ones for something else and just thought I'd throw it in .

Those are just results from quick lazy search so a proper search will provide better results.

http://www.ebay.co.uk/sch/i.html?_from=R40&_trksid=p2047675.m570.l2736&_nkw=pwm+AC+Motor+Speed+Controller+

[tigersaw]

If it was 'playing up' i.e. intermittent erratic operation I'd first clean it all up, check solder joints (no harm in wetting them all up again), checking resistors for value and mechanical stress (wobble them all and see if anything breaks).
If the caps are electolytic I'd change them if over 10 years old.

[Bibio]

Hi Lance, would something like this(link below) be any good?

I'm no an electronic guru so link might be completely useless to you :p
It's just so happens I'm currently looking at using one of the DC ones for something else and just thought I'd throw it in .

Those are just results from quick lazy search so a proper search will provide better results.

http://www.ebay.co.uk/sch/i.html?_from=R40&_trksid=p2047675.m570.l2736&_nkw=pwm+AC+Motor+Speed+Controller+

hehehee.. nope but thanks anyway :D

If it was 'playing up' i.e. intermittent erratic operation I'd first clean it all up, check solder joints (no harm in wetting them all up again), checking resistors for value and mechanical stress (wobble them all and see if anything breaks).
If the caps are electolytic I'd change them if over 10 years old.

i can see that one of the resistors is broken at the leg and the main power connector is wobbly (solder has come away from legs. i intend to sort the resistor (100k) and rejoin the connector legs.

yes the TT is about 20 years old.

i can pop a few pics up of the board if you like.

[tigersaw]

I'd repair the resistor, change the caps, repair obvious faults and see what happens.
I guess there is a variable in the mix somewhere to control it?

[Bibio]

here is a thread on another forum showing the board.

http://www.vinylengine.com/turntable_forum/viewtopic.php?f=45&t=54358

[Bibio]

I'd repair the resistor, change the caps, repair obvious faults and see what happens.
I guess there is a variable in the mix somewhere to control it?

yup. it controls the pulse i'm led to believe so it quietens down the motor vibration from the motor.

[21QUEST]

hehehee.. nope but thanks anyway :D
Bugs! :smt042

[tigersaw]

Thats the board?
Looks more like a DC motor controller, how many wires on the motor? Does it have a second set of wires for a hall effect feedback or just a single ribbon cable, i.e stepper motor?
Where did you get the idea of 110v from?

Looking at the pictures, I'd be looking for fatigue / heat damage and repairing what I found before replacing anything.

[Bibio]

well the motor it drives is an Airpax 9904-111-3181 110v 250rpm 50hz

http://uk.farnell.com/jsp/search/productdetail.jsp?SKU=1784855&MER=baynote-1784855-pr

supply is mains 240v

[tigersaw]

Oddly I dont see why the control board is so complicated - that motor is pretty precision by itself and the examples show simple wiring. The board in the picture is really busy, I can see crystals suggesting some sort of phase loop timing circuit, perhaps some A/C regenearation shenannegans.
I guess the knob sticking out the side is a speed control, and the platter has a strobe of some sort maybe?

[Bibio]

no strobe and yes it's a very complicated way of doing it and yes the knob is for changing between 33/45. the problem with these AC motors is rumble which is transferred into the TT causing audible smear of the sound like the lesser decks of pro-ject and such like use less complicated circuitry so the quieter you can make the motor the better the TT sounds. most cheep TT's just bolt/suspend the motor to the plinth but this sucker has its own housing and suspension for the motor.

thanks for your help so far tiger and it's much appreciated you taking the time to help.

i was going to order a load of resistors and do the lot as it's penny's but i think i'll fix the broken one first and solder the connectors back on and see how it goes.

BTW these boards were notorious for being unreliable.. lol

[tigersaw]

If there is no strobe / fine control then they must be confident of getting the speed absolutely right, hence I guess the complication. I imagine it converts 240v to DC, then regenerates a very pure AC supply for the motor, hence the reference crystals.

I used to have a mitchell engineering turntable, reputed to be a bit swish, but it had nowhere near the complexity as that.

[Bibio]

you had a gyro.. wow :-) i would love one of those decks. stupidly good and look the doggyz to.

there are trim pots to adjust to get it spot on. your more than probably right about the DC as i suspect he used part of the same design for the export and anniversary TT's which had DC motors or as you say it was to clean up the mains then get a nice steady AC sign wave.

[tigersaw]

You wont believe me when I tell you I got it from the dump..
I sold it on ebay as it was too good for me, my vinyl was played on a Rockola 448 and a seeburg jukebox.
Northern Soul was mastered to be played on such machines, thats when it sounded its best.

[Bibio]

you got a gyro out a dump and you sold it as 'it was to go for me'. your maaaaaad and i'm jealous :-)

i almost bought a second hand one in the late 80's from hifi corner in edinburgh as it was something stupid like £250 but decided i'll wait till my next pay.. next pay and gone, so i got pizzed instead.

[Bibio]

one of the mates has one of these
http://images.canadianlisted.com/nlarge/rock-ola-princess_5447252.jpg

and had one of these
http://www.retroaudiolab.com/pictures/rockola444.jpg

[tigersaw]

I know, but I like my music with clicks pops and crackles like the audio of the 60's. Heck, I listen to AM radio in the car because I think it sounds better.


Cool juke boxes - mine was the 448, probably same inside. Even listening to it selecting the record was like music to my ears. Sadly I parted with it to a collector for a lot of money, but sometimes you wonder if it was the right thing to do.

[Bibio]

ahhh the joys of vinyl. comes with that log fire sound of yesteryear :-)

digital just does not do it for me and to me it sounds sterile and soulless.

[tigersaw]

Now if they could just make digital sound like vinyl..

[Bibio]

funny they are going back to analogue mixing desks and tape for some new albums to get the authentic sound.. stupid people.. it's still digital on the disc you morons.. lol

ooohhh and i recall that there was a cd that came out with fake snap, crackle and pop sound.

[Messie]

Do these electronics come with grocer's apostrophes?
;)

[Bibio]

i'm happy as a pig in. replaced the resistor and soldered the connector, bingo we have a running motor again.. thats just saved me a fair few pennies :-)

[tigersaw]

Well done