D-AOC PCBs - the building and help Thread

[braeden]

Quick question

I recently fired up my D-AOC. I initially connected the primary windings around the wrong way (I am using the Musikding transformer). The yellow and white were connected together for 230V series operation... it was actually meant to be orange and white :

I have the unit wired up correctly now and the 24VAC/9VAC windings are working correctly and I have 6.3VDC trimmed for the heater supply and 12V regulated DC for the relays etc.

I'm not measuring any AC voltage at the 220VAC winding however. I had some sparks on the TL783 (B+ side) of the PCB and now my 2W resistors on that side are burnt out, as well as my zeners I am pretty sure.

Could this be the result of a faulty winding (from the manufacturer), is it possible that I have damaged the transformer?

Thanks everyone,
Braeden

 

[alexc]

If you are sure you have the primary of the transformer powered up correctly and still don't measure any ac voltage with the HV secondary winding disconnected and open circuited then yes you have fritzed the thing.

It's generally not that easy to burn a winding out - it takes a pretty willing fault condition.
Normally you would burn up other components before the transformer, but it's not unheard of either.

Anyway  - disconnect, carefully apply primary and check the o/c secondary.

Good luck.

 

[zayance]

There is also the fact that maybe, and it has been stated before on the thread, if you have a too high HT, because of higher mains etc..., then you'll need to bring it down with some high wattage resistor, i used 2.5K 25W or so iirc, enough to still be in the Vin-Vout max of the TL783, check the datasheet, as this will also frie the Regulator obviously...
Well that's if the Power transformer is ok as alexc has stated, and if wired correctly etc....

 

[braeden]

Thanks for the replies fellas.

This was a silly mistake and was the result of working in low light unfortunately.

I've ordered two new transformers from Musikding along with a whole new B+ section for the PSU.

It sucks that I'll have to wait another 2 weeks before it gets here but that's just how it goes I'm afraid!

Cheers,
Braeden

 

[druu]

Can anyone suggest on which Lundahl's to use for the outputs? Currently opting for LL1540's for input.

Thanks!

 

[protools]

LL5402

Best
WT

 

[druu]

I'm nearly at the wiring stage (just waiting for front panel to be laser etched) and just wondering how I would go about this;

I have these meters going in:
http://www.ebay.com.au/itm/Panel-VU-Meter-TN-73-0dB-1-288V-76x59mm-LED-lamp-NISSEI-/130384936913?pt=LH_DefaultDomain_0&hash=item1e5b8c3fd1

..and I'm also running Igor's bypass boards using 24v relays and using a Musukding toroid that has 24v output. I'm assuming I would go with a LM7824 for the Universal PSU reg? Also, how would I wire the lighting for the meters? They require ~3.6v - 5.2v according to the eBay link above.

Thanks in advance!

 

[druu]

I went to test voltages tonight after carefully mounting pcb and toroid into my chassis and wiring it up. I'm using a Musikding toroid I bought back in June which I think may have been the last one in stock as they don't list it anymore. After powering up and checking voltages, I'm only reading the 250v secondary! 24v and 9v secondaries show nothing.

Any advice on where to go from here? I've emailed Musikding but don't like my chances as I bought the item back in early June though its been sitting on the shelf unopened until tonight, great! . Any advice appreciated!

 

[Script]

Are you sure it's wired correctly? If so, try scratching the copper wires clean with a sharp knife. Could be there's a tiny film of non-conductive stuff around the copper (rather orange or pale red than copper coloured). Not sure that's the case, but you might want to give it a try. I remember having had a similar problem and this fixed it.

 

[druu]

Thanks Script. Yes, wired correctly, primaries wired for 240v (orang/white tied together and yellow/lilac for live/neutral). I did scrape the 9v wires with a knife, none of the other wires had the coating though. I noticed this before mounting into the chassis.

 

[Script]

Can't help you with the wiring of the toroidal. You mounted the regulators off board? Check the wirings/orientation and whether you not accidentally swapped the 9V and 24V ones. Also, the board itself might want to be grounded. Other than that, don't know. Does the toroidal put out the correct voltages?

 

[druu]

My wiring is correct. As mentioned above, input 240v, ouput 250v OK but 9v and 24v nothing at all. Definitely a dodgy toroid. I read earlier in the thread where some users had problems with Musikding toroids. Anyone care to chime in?

 

[Script]

Guess you have checked already. Does the toroidal itself put out the correct/any voltage, that is, measured across bare secondary wires (9V & 24V) when not connected to the board? If it doesn't, I'd contact Music-thing and ask for a refund.

 

[druu]

No nothing at all on 24v or 9v. 250v secondary is working as it should.

I've emailed them but no reply yet, hopefully they will refund as it wasn't exactly cheap!

 

[druu]

I managed to get the 9v secondaries working, not sure how, I measured continuity on the secondaries and it was definitely there and wiring it back up it showed the second time around. 24v still shows nothing (but continuity is also there).

Anyway I also managed to get 6.3v from the heater, before and after plugging the tubes, which is good. Though the LM350T is isolated from the heatsink, the middle is somehow showing continuity to ground? 6.3v is still there though. It's quite hot so will have to relocate, but is the LM350 fried?

A major concern is that i'm getting 300+v from measuring the inputs of the 250v secondaries. I quickly tested some points and after Rx28 I'm getting 500v+ :S I'm using the silkscreened values of 470r+47r.

Mains here is at ~245v. Any advice? Middle leg of the LM783 is showing very high too. Also fried?

 

[druu]

Disregard the above post, I've been schooled by zayance over email and all is well. thanks zayance (what a champ!).

 

[Script]

Please share 

 

[zayance]

Yes it would have been better to explain for all here.
Basically nothing much than simple electronics and calculus that we tend to forget when buidling things.
For the HT, it's the problem i had, Mains can cause the secondary to be too high, his is at 300VAC.
Converted into DC, shows that you of course hit the TL783 too hard for it's regulation range beeing max 125V, and from the circuit designed for having about 240VDC OUT.
So as mentionned in some posts in this thread, having a higher value and power for R1 can help dropping HT to a more reasonnable value for the VReg, i personnaly had to use about 2.4K, etc...
For the 24V side, it was nothing more than a wrong way of measuring.

Nothing of a champ really

T.

 

[[silent:arts]]

But one reason why there is R1 ...

 

[zayance]

Well maybe better to leave R1 for current limiting and drop AC before entering the PCB as some have said doing on old posts, true.