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 Forum index » DIY Hardware and Software » Circuit Bending
Locating Timer Resistor or Oscillator on VTech Alphabet Desk
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WabashDiscord



Joined: Sep 02, 2013
Posts: 4
Location: Wabash River, Indiana

PostPosted: Wed Dec 18, 2013 5:51 pm    Post subject: Locating Timer Resistor or Oscillator on VTech Alphabet Desk
Subject description: Having difficulty finding the timer control for this device.
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Good evening everyone,

New to the forums. Have been reading for a few months now and wanting to start posting.

I recently modified a VTech Alphabet Desk and I am having a lot of fun developing various sounds on the device. However, I cannot locate the timer resistor or crystal oscillator that is controlling the timer for the circuit.

I have pitch bent other devices, but this one seems elusive. Some of the glitches are very fast and jumbled, and a pitch/timer pot would help hear some of the complex sounds being emitted by the device.

I have also tried the starved battery pot and it works to a point, but the circuit usually gets upset and crashes, shutting down.

Attached are some pictures of the board. Any help or advice would be greatly appreciated.


20131218_194044.jpg
 Description:
Front of the VTech Alphabet Desk circuit board
 Filesize:  1.74 MB
 Viewed:  44 Time(s)
This image has been reduced to fit the page. Click on it to enlarge.

20131218_194044.jpg



20131218_194112.jpg
 Description:
Back of the VTech Alphabet Desk circuit board
 Filesize:  1.98 MB
 Viewed:  34 Time(s)
This image has been reduced to fit the page. Click on it to enlarge.

20131218_194112.jpg


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PHOBoS



Joined: Jan 14, 2010
Posts: 1799
Location: Moon Base
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PostPosted: Thu Dec 19, 2013 6:56 am    Post subject: Reply with quote  Mark this post and the followings unread

welcome party!

hmm I've bend a vtech thing before and I don't think I found anything to control the pitch either (else I would probably have added some pitch conrol).
I know there are PIC's that can run on an internal oscillator without any external components,. so it might be that it works that way.

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WabashDiscord



Joined: Sep 02, 2013
Posts: 4
Location: Wabash River, Indiana

PostPosted: Thu Dec 19, 2013 11:18 am    Post subject: Reply with quote  Mark this post and the followings unread

Thanks. I don't have a lot of experience with circuit bending, but this was a first. Good to know I wasn't the only one coming up against adversity with this VTech.

Thankfully, I can sample and slow down digitally. Would be nice if I could do it live as well.

We'll take a stab at writing VTech for a datasheet. Ha!

Thank you again!
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WabashDiscord



Joined: Sep 02, 2013
Posts: 4
Location: Wabash River, Indiana

PostPosted: Sat Dec 21, 2013 5:44 am    Post subject: Reply with quote  Mark this post and the followings unread

As expected, VTech won't share their datasheets or information. Oh well. We'll keep plugging away on this and other devices.
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Mikmo



Joined: Dec 01, 2005
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Location: Copenhagen - Denmark

PostPosted: Sat Jan 04, 2014 4:31 pm    Post subject: Reply with quote  Mark this post and the followings unread

Check here for pitch mod:

http://www.sailormouth.org/binst.html

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Bogus Noise



Joined: Jun 03, 2009
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Location: Sheffield

PostPosted: Sun Jan 12, 2014 1:35 am    Post subject: Reply with quote  Mark this post and the followings unread

There's a lot of different models of Alphabet Desk, and the SailorMouth one is for the white front, blue base version. The white front/red base is more awkward as it seems the clock osc is built into one of the chips. The one in the original question is the yellow front/blue base model, which I have around here but haven't had a chance to open up yet. I would suspect R9 and R19 by the two chips would be the place to look, as it's a similar (but different) board to the Letter Fun PC, but not sure it'll definitely work, as I didn't add a pitch mod to the Letter Fun at the time either!
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PHOBoS



Joined: Jan 14, 2010
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Location: Moon Base
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PostPosted: Sun Jan 12, 2014 4:42 am    Post subject: Reply with quote  Mark this post and the followings unread

WabashDiscord wrote:
As expected, VTech won't share their datasheets or information. Oh well. We'll keep plugging away on this and other devices.

you asked ?, thanks for that Very Happy too bad they don't share them, that would have been very interesting Twisted Evil

Bogus Noise wrote:
There's a lot of different models of Alphabet Desk, and the SailorMouth one is for the white front, blue base version.

I don't know about the alphabet desk (no reson to doubt you though) but I can confirm from first hand experience that there are indeed differences
between the 'same' toys. At some point I got myself a "sprekend computer vriendje" (dutch) and started bending. I also drew a schematic
of part of the circuit to get an idea what certain chips might be for. So I spend some time on that and then I fried the chip to a point that it's
permanently bend Sad Not wanting to waste the time I put into it, I searched for a replacement and found one. It looked exactly the same
but when I opened it up the PCB was very differet, and the schematic I'd drawn was pretty useless,. Mad

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Bogus Noise



Joined: Jun 03, 2009
Posts: 59
Location: Sheffield

PostPosted: Sun Jan 12, 2014 5:19 am    Post subject: Reply with quote  Mark this post and the followings unread

PHOBoS wrote:
WabashDiscord wrote:
As expected, VTech won't share their datasheets or information. Oh well. We'll keep plugging away on this and other devices.

you asked ?, thanks for that Very Happy too bad they don't share them, that would have been very interesting Twisted Evil

Bogus Noise wrote:
There's a lot of different models of Alphabet Desk, and the SailorMouth one is for the white front, blue base version.

I don't know about the alphabet desk (no reson to doubt you though) but I can confirm from first hand experience that there are indeed differences
between the 'same' toys. At some point I got myself a "sprekend computer vriendje" (dutch) and started bending. I also drew a schematic
of part of the circuit to get an idea what certain chips might be for. So I spend some time on that and then I fried the chip to a point that it's
permanently bend Sad Not wanting to waste the time I put into it, I searched for a replacement and found one. It looked exactly the same
but when I opened it up the PCB was very differet, and the schematic I'd drawn was pretty useless,. Mad

Yeah, that happens quite a bit! I can confirm that the Sailormouth Alpha Desk and this one are the ones mentioned though, I should've said I hadn't properly tested the yellow/blue one for bends but I was in danger of rambling Laughing
I have quite a few variants of seemingly identical toys here... there's about 6 versions of the Hing Hon that I know of! I almost mentioned the red Alphabet Desk Phonics in the previous post, as that has two board variants that I've found, one is unbendable, the other does this:

http://www.youtube.com/watch?v=YG_GQ7zDGLc

Sometimes though, the alternate board will be the same circuit but differently laid out, or designed for SMD instead of through-hole components. That's helpful, as retracing a circuit can be quicker than making a whole new design!

I've also had a Pro37 keyboard knocking around to rebuild to a previous design of mine, but only had sketchy notes around as it was from aaaages ago. I had already drilled and mounted the controls, then realised the board was different. Bought another one, was also this new variant, but I wanted to get both types working the same as the first one I bent. After a few months I finally tracked down one of the proper ones, and it was only *then* that I realised the entire control panel was different as well Rolling Eyes

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