Vintage Synth Repair

Hi Tom,

Did you manage to solve the problem? The backlight should be drawing 1-2 mA @ 100-110 VAC, from the readings you've reported I think that there is a break in the backlight circuit (i.e. the inverter runs freely, hence the higher frequency and voltage). I suggest you try to put a 120k resistor across the output of the backlight circuit (1/4 W or higher rating) and measure voltage and frequency again. This load is close to what a good backlight should represent to the circuit, so the values on the resistor should be near to those suggested earlier on the thread (200-400 Hz @ 100-110 VAC).

If that is what you measure, chances are that your backlight is damaged or the leads are not properly attached to the poles (or the wires, connectors are faulty). Do you have a picture of your backlight, also covering the area where leads are attached to it?

Cheers,
synthjoe

--- In vintagesynthrepair@yahoogroups.com, "Quazimodo" <noddyspuncture@...> wrote:
>
> Many thanks for the info Noel..!
> Cheers.
> TOM
> 
> 
> 
> --- In vintagesynthrepair@yahoogroups.com, NoëlBuhagiar <laser@> wrote:
> >
> > Hi,
> > 
> > Maybe of help to you.. I’d rather check it using a scope.
> > I checked output of similar 01WFD model connected to a GlowSafe backlight:
> > Measured between 200 to 250Vp-p (peak-to-peak) at around 500Hz
> > 
> > I don’t think measuring voltage using a multimeter is accurate enough
> > Also make sure the circuit is loaded with a backlight when measuring.
> > 
> > When original Korg backlight wears out it attenuates (shorts) the output and no voltage is obtained using the scope.
> > The current is very weak and easily falls to 0
> > Also check elect.caps for bad ESR and check value or better replace the cap. at transistors base if necessary
> > 
> > Could you check your backlights on another circuit to make sure these work?
> > Good luck once again
> > 
> > 
> > 
> > 
> > From: Quazimodo 
> > Sent: Tuesday, August 07, 2012 11:18 AM
> > To: vintagesynthrepair@yahoogroups.com 
> > Subject: [vintagesynthrepair] Re: Backlight Revisited...
> > 
> >   
> > No cracks - all looks fine.
> > Seems no matter what I change or do... it stays the same...;c(
> > 
> > --- In mailto:vintagesynthrepair%40yahoogroups.com, "jammie" <jammie.emma@> wrote:
> > >
> > > have you got any cracks on the pcb as i have had wavestations psu crack on the fixing holes
> > > ----- Original Message ----- 
> > > From: jammie 
> > > To: mailto:vintagesynthrepair%40yahoogroups.com 
> > > Sent: Monday, August 06, 2012 11:43 PM
> > > Subject: Re: [vintagesynthrepair] Re: Backlight Revisited...
> > > 
> > > 
> > > 
> > > 
> > > that with in tolerance
> > > 
> > > the circuit is only a few resistors 1 switching transistor and 2 caps and the step up transformer
> > > ----- Original Message ----- 
> > > From: Quazimodo 
> > > To: mailto:vintagesynthrepair%40yahoogroups.com 
> > > Sent: Monday, August 06, 2012 11:13 PM
> > > Subject: [vintagesynthrepair] Re: Backlight Revisited...
> > > 
> > > 
> > > 
> > > Yes Jammie, I am getting the 5volts... well, actually around 5.5v
> > > 
> > > ...it's weird one this!
> > > 
> > > --- In mailto:vintagesynthrepair%40yahoogroups.com, "jammie" <jammie.emma@> wrote:
> > > >
> > > > are you getting 5v at the incoming circuit or is this voltage higher
> > > > ----- Original Message ----- 
> > > > From: Quazimodo 
> > > > To: mailto:vintagesynthrepair%40yahoogroups.com 
> > > > Sent: Monday, August 06, 2012 10:39 PM
> > > > Subject: [vintagesynthrepair] Re: Backlight Revisited...
> > > > 
> > > > 
> > > > 
> > > > Hello again,
> > > > 
> > > > OK I swapped the smoothing Capacitor C28.
> > > > 
> > > > No change... so to date I have checked the transistor, C28 and also the actual foil itself.
> > > > 
> > > > Stil getting 166 volts AC at around 2kHz.
> > > > 
> > > > I was thinking of changing C26 and C29 as well - could either of these be causing the symptoms?
> > > > 
> > > > Also, the transformer itself... it is obviously 'working' but do these either work or not - can they give different results?
> > > > 
> > > > I know you suggest going the LCD route - but as I have already got two new foils, I'd really rather get it fixed if at all possible... but this is fast becoming an epic saga!
> > > > 
> > > > Cheers,
> > > > TOM
> > > > 
> > > > --- In mailto:vintagesynthrepair%40yahoogroups.com, "jammie" <jammie.emma@> wrote:
> > > > >
> > > > > check the smoothing capacitor c28 the transformer is fixed uptransforms to the correct voltage for input 
> > > > > 
> > > > > so if the input ac voltage is wrong then it gets multiplied by the transformer
> > > > > 
> > > > > so the input voltage to the transformer has to be wrong
> > > > > 
> > > > > the transistor switches the dc voltage of 5v into a small ac voltage 
> > > > > 
> > > > > its the same with all efoil invertors except on the korgs they have the components on board a lot use inverter chips which are the same but in a white box this is so if the invertor fails you can just swap it out 
> > > > > 
> > > > > on the korgs you have to find which parts are at fualt and change them
> > > > > 
> > > > > i would just remove the invertor circuit and fit an led lcd instead 
> > > > > 
> > > > > then all you have todo is put a current limiting resistor to the manufacturers specs for the led back light from 5v line to the + of the efiol output pin on the psu
> > > > > 
> > > > > then you can use the same cable for the back light as the original efiol cable
> > > > > 
> > > > > the led backlights from rs work just fitted one to a kurzweil k2000
> > > > > 
> > > > > which uses the same footprint as the wavestation but the negative blue ones are on back order until november 
> > > > > ----- Original Message ----- 
> > > > > From: scott frye 
> > > > > To: mailto:vintagesynthrepair%40yahoogroups.com 
> > > > > Sent: Sunday, August 05, 2012 2:49 PM
> > > > > Subject: [vintagesynthrepair] Re: Backlight Revisited...
> > > > > 
> > > > > 
> > > > > 
> > > > > Is the rep rate of the AC frequency set internally on the transformer
> > > > > module?....If not, there must be an external timing component that's
> > > > > making the thing run too fast.
> > > > > A resonator?....A timing capacitor?
> > > > > 
> > > > > -- 
> > > > > Scott Frye
> > > > > 
> > > > > Audio-fixation.net
> > > > > 
> > > > > Vermont
> > > > >
> > > >
> > >
> >
>