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 Forum index » DIY Hardware and Software » Ken Stone designs - CGS
VCS confusion!
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The Bad Producer



Joined: Mar 08, 2009
Posts: 255
Location: The Manhole

PostPosted: Sun Aug 08, 2010 9:20 am    Post subject: VCS confusion! Reply with quote  Mark this post and the followings unread

I've just been building a new VCS, and I'm a little confused, maybe someone can help!

I have one working fine, after I realised that there is a wiring error on CGS, which suggests that Rise Rate and Fall Rate should go to -15V, rather than GND as on the schematic... This error led to the rise/fall rate pots only being active in the last 1/4 turn...

I started building another which doesn't work, I assumed it was the transistors - everything else looks cool - but upon further inspection on the PCB where it states '2N3904' '2N3906' it appears to show the pin out of BC547/BC557 ie the ECB is the wrong way round for my 2N3904/6's...

On the one that is working I have the 2N3904/6's as per the PCB text, and that works, is there any other reason why the new one doesn't work? Is there a standard pinout for 2N3904/6's?...

I did switch the transistors round and it sort of worked, it won't cycle, and the trigger in/end out doesn't work, but it will slew/trigger through the input and feed that to all the outputs... man I'm confused! I feel maybe I should sleep on it, or throw the bloody thing in the bin!

Would having transistors the wrong way round fry the LM3900, or other chips? Also the LED driver didn't work until I swapped the transistor around in respect of the PCB text, at least that works!

Err, more a tale of DIY pain I suppose... I'm sure I'll get to the bottom of it!

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andrewF



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PostPosted: Mon Aug 09, 2010 12:04 am    Post subject: Reply with quote  Mark this post and the followings unread

there was some discussion a year or 2 back about transistors having a different pinout depending upon the manufacturer, maybe the culprits were 2N3904/6's.

i doubt having the trannies in the wrong way will damage the LM3900, most of them are in different parts of the cct. the only one close to the LM3900 is the 3906 near the 100k trimpot (on the schematic) and that has a 220k resistor between them which should protect it, for a while at least.

if just the trigger in/end out doesn't work, you are almost there. Have a good check of the components and soldering around this part of the cct (The section at the top of the schematic)

If you found an error on the schematic it is best to email Ken and let him know, he might not see it here.

have some more coffee!! !
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The Bad Producer



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PostPosted: Mon Aug 09, 2010 3:31 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi Andrew,

Yes, I got round to reading that part of Ken's site - very interesting! I ended up getting my transistor checker out, desoldering all the transistors and checking them one by one, seems I had both pinouts in one batch - which is a bit annoying as I only ever use the same supplier and they've not changed the order number -either that or I've bought/inherited some from somewhere else and forgotten about it!

So all is good now, it was a little annoying as I was building two for a friend, and another two for myself, so I had a lot of desoldering to do!

Thanks!

Charlie

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TekniK



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PostPosted: Mon Aug 09, 2010 9:47 am    Post subject: Reply with quote  Mark this post and the followings unread

http://www.cgs.synth.net/modules/parts_faq.html
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