Power woes/SVCO

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Paradigm X
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Power woes/SVCO

Post by Paradigm X » Sun Jan 19, 2020 12:06 pm

Hi

SO i stupidly got carried away last night and tried to plug in a new power cable into another vco (diy thomas henry x4046 vco) while the modular was powered. I think i connected +15v to ground, got an impressive spark and the SVCO 'crashed' (reset to red LFO mode not the green vco mode it was in).

Now the svco seems broken :(

It seems to work ok (i.e. cvs change the pitch as expected, not sure about v/oct) with the waveshape as 12oclock. However, if i move the shape knob, or apply cv i get a horrendous noisy crackling sound. not good. particularly bad on the saw/tri.

If you could offer any advice id be very grateful.

It was powered with a Oakley PSU Issue 2 and PA30, with 2 dizzys in 2 cabinets. A sympleseq and MOTM120 were both plugged into the dizzy and both seem fine. Ive nto tried anything else yet.

So generally speaking, what would happen to the oakley psu under this situation, and what may have happened to the svco ? I havent got schematics for that as it was a Krisp1 build. Happy to buy them tho. Im hoping its a case of switching a few ics but im clueless tbh. :(

I think i need to put power switches on each case, ive just reread the builders manual and the user manual and it says dpst, but is there a power/watt/voltage minimum rating i need? is it ok to put a metal switch in a metal case?

im going to plug in my full oakley vco now which works but is not calibrated, and see what else is damaged
(edit thankfully the multimix and ringmod both seem to have survived. man that ringmod sounds amazing).

sorry to trouble you again.

many thanks

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Re: Power woes/SVCO

Post by Synthbuilder » Mon Jan 20, 2020 4:16 am

Firstly, before you do anything else, measure the voltage on both of the rails with respect to 0V. Make sure that it is still +15V and -15V on the positive and negative rails respectively. If all is well then I suspect the problem is the SVCO alone.

Contact me by e-mail for schematics for the SVCO.

The first thing to try is to make sure the VCO is still tracking and that the octave switch is switching octaves. If not suspect every LT1013 on the SVCO and SVCO Octave board, particularly U3 on the SVCO main board. Some versions of the LT1013s (I think it's the Texas ones) seem to be very prone to dying if one of the supply rails drop out while the other rail is still high.

It may be worth replacing D4 and D5 on the PSU board with 1N5819 diodes as these seem to be better protecting badly designed ICs from dying when one of the rails drop out.

Tony

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Re: Power woes/SVCO

Post by Synthbuilder » Mon Jan 20, 2020 4:22 am

Paradigm X wrote:
Sun Jan 19, 2020 12:06 pm
I think i need to put power switches on each case, ive just reread the builders manual and the user manual and it says dpst, but is there a power/watt/voltage minimum rating i need?
At least 5A AC. Most bigger switches are rated at 240V AC, but anything over 100V AC will be fine. You'll notice that DC ratings of switches will be much lower, but you are switching AC so the AC figure is the important one.
is it ok to put a metal switch in a metal case?
Yes.

However, for power supplies with an internal main transformer, ie. not those with a PA20/30 linelump, I would recommend plastic ones. But metal ones can be used if the case is properly earthed.

Tony

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Re: Power woes/SVCO

Post by Paradigm X » Mon Jan 20, 2020 5:45 am

yikes. I measured the dizzy in the second case as it was easy to get to, and got +22v / -21.8V. thats obviosuly wrong. i shut everything down immediately. I did run everything last night for about half an hour i didnt think the psu would be broken as it seemed to work.

I didnt retry the svco but yesterday the octave switch worked fine, and it played different notes from a basic baby8 sequencer.

edit - thanks just saw the info on switches too. i was planning on putting the switch on the little metal side bars analog crafstman made once, they are half u wide and cover the side racks. i thought a switch and the 3 leds would be useful. ill have a look for a plastic one, many thanks for the specs.

cheers, Ben

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Re: Power woes/SVCO

Post by Synthbuilder » Mon Jan 20, 2020 6:44 am

Paradigm X wrote:
Mon Jan 20, 2020 5:45 am
yikes. I measured the dizzy in the second case as it was easy to get to, and got +22v / -21.8V. thats obviously wrong.
Yeah, that's not good. Fortunately, most ICs can handle 36V so 44V may not be enough to damage them in the short term.

Interesting that the PSU issue 2 died. They're pretty robust, but maybe a short from +15V to -15V would fry them. They should easily be able to cope with shorts to 0V though. But the fact you said it sparked does suggest some big currents going places they shouldn't.

Either way, you need to look at your PSU before you power up any of your cases again. Clearly it's not regulating, so the usual suspects would be Q1 and U1. I think the negative rail may start behaving once the positive one is fixed.

Tony

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Re: Power woes/SVCO

Post by Paradigm X » Mon Jan 20, 2020 7:03 am

yeah i was ferreting about with a power cable and there was a clear red spark and a noise. it was only instantaneous as i didnt get the header on correctly. not checked that other vco yet either. i was surprised as it was a plastic mta cable cover over the pins.

i must learn to turn it off. a power switch would help immensely. i cant remember why i didnt, it was ages ago i built the psus. ill fit one as i repair the psu.

Ok ill have a loot at the psu . luckily having one psu/dizzy for every 10u saved over half the modules from potential damage. i didnt even reconnect the common banana ground i used to use.

many thanks.

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Re: Power woes/SVCO

Post by Paradigm X » Mon Jan 20, 2020 7:35 am

hmm the lm723cn is out of stock at rapid, rs, farnell, cpc and rapid. Bitsbox have some tho, and they seem reputable? It might be worth buying a few for spares.

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Re: Power woes/SVCO

Post by Synthbuilder » Mon Jan 20, 2020 8:10 am

Sadly, the LM723 was deleted a couple of years ago. Hence the reason I now have a new PSU and VCO boards.

I have LM723CN too, 1GBP each. Probably not worth getting them from me though unless you're ordering some more boards. Bits Box will be cheaper.

Tony

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Re: Power woes/SVCO

Post by Paradigm X » Mon Jan 20, 2020 8:25 am

brilliant thank you. i was going to place an order next week after i get paid, i really want a disconuity before they go and the output module looks really useful too. man i could buy a load, the delay, chorus and asv all highly desired.

if the vco needs one too ill definitely buy a few spares.

I cant beleive i havent got any, i normally buy a few at a time when i buy ics, ive got a drawer full of hundreds but not the right ones sadly.

i might try swapping it from the working psu to the other to test it. But if q1 is broken will that kill the working lm723 in a test scenario?

thanks so much for all your help it is much appreciated.

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Re: Power woes/SVCO

Post by Synthbuilder » Mon Jan 20, 2020 11:30 am

Paradigm X wrote:
Mon Jan 20, 2020 8:25 am
if the vco needs one too ill definitely buy a few spares.
Just the older versions of the 2U wide VCO. The SVCO and issue 7 VCO use a different reference and supply circuit.
But if q1 is broken will that kill the working lm723 in a test scenario?
Possibly. It depends on how Q1 is broken. I think if there is a short between all three pins of Q1 then that could possibly damage the LM723. I think Q1 is the more likely to have died in your case.

If it were mine, I'd pull U1 out, short out pins 2 and 10 of U1's IC socket. Then power up and measure the +15V output rail. If it's still 22V or so, I reckon that Q1 is fried. I'd then replace both U1 and Q1. If you get 0V without U1 in place and pins 2 and 10 shorted, then Q1 may well be still working but U1 is dead. But even so, I'd still be tempted to replace both devices.

Tony

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Re: Power woes/SVCO

Post by Paradigm X » Mon Jan 20, 2020 3:26 pm

thank you very much tony, ill take it down and have a look shortly.

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Re: Power woes/SVCO

Post by Paradigm X » Mon Jan 20, 2020 4:35 pm

ok, i unglugged the entire backplate, and remeasured.

With the LM723 in, i get 23.0/-23.1

with pins 2 and 10 shorted, the +ve LED does not light, and i get -0.5v (minus!) on the positive rail, and -10.1 on the negative.

Obvious not right.

ILl order some new lm723 (i do have an older vco so def want to grab spares now) and i have some 1n5817 (in a rapid bag with 'oakley' as a reference! :hihi: ) are they equivalent to 1n5819? ill order some of the latter if not. While im making an order, ill also get a few of the TIP135cs, is there anything else i should replace too?

many thanks, regards
Ben

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Re: Power woes/SVCO

Post by Synthbuilder » Tue Jan 21, 2020 4:25 am

Paradigm X wrote:
Mon Jan 20, 2020 4:35 pm
With the LM723 in, i get 23.0/-23.1

with pins 2 and 10 shorted, the +ve LED does not light, and i get -0.5v (minus!) on the positive rail, and -10.1 on the negative.
Q1 may well be working then. Remember that the negative rail takes its cue from the positive rail. So if the the positive rail is not somewhere near +15V then the negative rail won't be working properly. So I think once the LM723 is replaced there is a good chance things will work again as they should. But it'll probably still be worth replacing both U1 and Q1 while you're at it.

The small negative voltage on the positive rail is just D4 doing it's job. I forgot about the action of D4 before when I said 0V.

The 1N5817 are only 20V devices. It's best to use the 1N5819 which is the 40V version.

Tony

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Re: Power woes/SVCO

Post by Paradigm X » Tue Jan 21, 2020 6:24 am

Cool, thanks again.

Ill order the correct parts. those TIP35cs are 3£ each on farnell and £1 each on bitsbox. Weird.

Also, just so i understand, should the fuses not have blown when i did that? or is that just for if i plug in too many modules or something?

thanks, Ben

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Re: Power woes/SVCO

Post by Synthbuilder » Tue Jan 21, 2020 7:46 am

Paradigm X wrote:
Tue Jan 21, 2020 6:24 am
should the fuses not have blown when i did that?
Fuses are relatively slow in responding to over current. They are there mostly to protect the mains transformer or line lump from overheating and burning out if the PSU starts to take too much current. The PSU's own electronics should protect itself. Clearly though in this case it didn't. Unfortunately, I can't say exactly what went wrong. But connecting a module incorrectly when the power is on causes very high currents to flow very quickly and sporadically. Even the best protection circuits can sometimes fail to do their job in these extreme and rare cases.

Tony

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Re: Power woes/SVCO

Post by Paradigm X » Tue Jan 21, 2020 9:51 am

yeah sorry wasnt a criticism of the design, just trying to understand these things. Directly connecting either ground or -15v to 15v is a pretty extreme example. no matter how much you idiot proof something theres always a bigger idiot! :party:

iver ordered the parts from bitsbox. when they arrive, ill replace q1, u1, and the diodes, and add a switch, then do the diodes and switch on the other unit.

then ive got to figure out what ive done to the svco (and possibly the other non oakley VC0)

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Re: Power woes/SVCO

Post by Synthbuilder » Tue Jan 21, 2020 10:51 am

Paradigm X wrote:
Tue Jan 21, 2020 9:51 am
Directly connecting either ground or -15v to 15v is a pretty extreme example. no matter how much you idiot proof something theres always a bigger idiot! :party:
:hihi:

But connecting either 15V to 0V (ground) is fine. Indeed, it's in the Builder Guide as one of test procedures to check the current limit. But I've never connected the +15V to -15V to see what happens. That could indeed be the Achilles heel. Generally though that's unlikely to happen. The thing is with making a connection while the unit is powered up produces all sorts of possible combinations as the four contacts in the socket meet at slightly different times with the contacts on the header. Plus you get an inrush current through only partially made contacts. This can actually damage the socket and header contacts too.

Tony

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Re: Power woes/SVCO

Post by Paradigm X » Wed Feb 05, 2020 3:32 pm

ok, PSU is now working, +15.00 and -14.95 assume close enough. new diodes and switch added, and i must do that to the other psu as well.

i plugged the svco back in and had a play.

it seems that just the waveshape pot causes the crackle either side of 12 oclock. the shape cv afaict seems to work ok - get the expected PWM type sound without any crackle. all other controls seem to work as usual.

so the obvious culprit would seem to be the pot but before i take it all apart is there anything else i should look for as well?

many thanks, Ben

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Re: Power woes/SVCO

Post by Synthbuilder » Wed Feb 05, 2020 4:33 pm

Paradigm X wrote:
Wed Feb 05, 2020 3:32 pm
... so the obvious culprit would seem to be the pot but before i take it all apart is there anything else i should look for as well?
If you have a scope then have a look at the voltage on the wiper (middle pin) of the pot as you turn it. A crackle on the audio will make the line on the scope go all bouncy. A good pot should produce a flat horizontal line that moves smoothly from the bottom to the top as you rotate the pot.

The smallest of small drops of DeOxit F5 applied to just above the pot's middle pin while the module is held so that the pot's pins are facing upwards should be enough to get rid of any dirt/dust on the track. Rotate the pot shaft to allow the fluid to move across the track. Never spray F5 into a pot, just spray a bit in the can's plastic lid and with a small flat blade screwdriver tip transfer the fluid to the pot.

Tony

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Re: Power woes/SVCO

Post by Paradigm X » Thu Feb 06, 2020 7:45 am

Hi, thanks again.

I have got a scope but its at another location atm and im not completely sure i know how to use it - on my ever increasing to do list.

Is a multimeter any use?

I should have mentioned, it doesnt sound like a typical worn out pot, more 'digital' crackles. It worked fine before i mispowered everything.

I do have some servisol super 10 - just wondering if that would work? that deoxit stuff is pretty pricey. Will get some tho if needed.

Many thanks, Ben

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Re: Power woes/SVCO

Post by Synthbuilder » Thu Feb 06, 2020 11:12 am

Paradigm X wrote:
Thu Feb 06, 2020 7:45 am
Is a multimeter any use?
Probably not if it's a standard digital one as they tend to smooth out any readings so you don't get to see the little wiggles produced as you move the wiper across the worn bit.
I should have mentioned, it doesnt sound like a typical worn out pot, more 'digital' crackles.
If the Shape CV input doesn't cause the same crackling sound the problem is likely to be the shape pot. Use a slow moving triangle wave LFO to verify that the shape can be smoothly modulated. If you get the crackles with an external CV the problem is clearly within the SVCO's circuitry.
I do have some servisol super 10 - just wondering if that would work?
Probably. It's not as good as F5 but it's worth a try before replacing the pot. Just remember to go easy on the application. The wetted end of a screwdriver tip is often all you need.

Tony

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Re: Power woes/SVCO

Post by Paradigm X » Fri Feb 07, 2020 5:06 am

Awesome, thanks. Sorry didnt mean to second guess you just making sure i explained the problem as best i could. The CV does seem to produce a smooth crackle free 'morph' from saw to tri and PWM on the square

Many thanks
Ben

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Re: Power woes/SVCO

Post by Synthbuilder » Fri Feb 07, 2020 5:24 am

Paradigm X wrote:
Fri Feb 07, 2020 5:06 am
Awesome, thanks. Sorry didnt mean to second guess you just making sure i explained the problem as best i could. The CV does seem to produce a smooth crackle free 'morph' from saw to tri and PWM on the square.
No need to apologise. It's not easy to fault find via the medium of forum posts or e-mails, so the more information about the problem we can share the better.

It does sound a like dirty pot though, so give it a clean and wiggle first and then replace if necessary.

It'll be well worth getting your scope back too. It is, without doubt, the most important piece of test equipment you can have bar your ears and an amp.

Tony

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Re: Power woes/SVCO

Post by Paradigm X » Fri Feb 07, 2020 6:06 am

Thanks Tony, I appreciate that. I do feel bad asking lots of what are probably quite basic queries. And having to ask for help after doing stupid things like this :hihi: well i wont be doing that again.

I will get the oscilloscope this weekend, need to learn how to use it.

Thanks as always, have a nice weekend.

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