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WabashDiscord
Joined: Sep 02, 2013
Posts: 4
Location: Wabash River, Indiana
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 Posted: 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.
| Description: |
| Front of the VTech Alphabet Desk circuit board |
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1.74 MB |
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41 Time(s) |
| This image has been reduced to fit the page. Click on it to enlarge. |
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| Description: |
| Back of the VTech Alphabet Desk circuit board |
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| Filesize: |
1.98 MB |
| Viewed: |
31 Time(s) |
| This image has been reduced to fit the page. Click on it to enlarge. |
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PHOBoS
Joined: Jan 14, 2010
Posts: 1652
Location: Moon Base
Audio files: 333
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| Posted: Thu Dec 19, 2013 6:56 am Post subject:
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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.
_________________
"My perf, it's full of holes!"
http://phobos.000space.com/ http://www.acidtrash.com/ Stickney Synthyards |
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WabashDiscord
Joined: Sep 02, 2013
Posts: 4
Location: Wabash River, Indiana
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| Posted: Thu Dec 19, 2013 11:18 am Post subject:
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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
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| Posted: Sat Dec 21, 2013 5:44 am Post subject:
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| 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
Posts: 150
Location: Copenhagen - Denmark
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Bogus Noise
Joined: Jun 03, 2009
Posts: 59
Location: Sheffield
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| Posted: Sun Jan 12, 2014 1:35 am Post subject:
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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!
_________________
Circuit Bent Sonic Absurdity:
www.bogus-noise.co.uk
http://www.youtube.com/user/BogusNoise |
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PHOBoS
Joined: Jan 14, 2010
Posts: 1652
Location: Moon Base
Audio files: 333
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| Posted: Sun Jan 12, 2014 4:42 am Post subject:
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| 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  too bad they don't share them, that would have been very interesting 
| 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  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,. 
_________________
"My perf, it's full of holes!"
http://phobos.000space.com/ http://www.acidtrash.com/ Stickney Synthyards |
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Bogus Noise
Joined: Jun 03, 2009
Posts: 59
Location: Sheffield
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| Posted: Sun Jan 12, 2014 5:19 am Post subject:
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| 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 too bad they don't share them, that would have been very interesting
| 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 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,. |
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 
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 
_________________
Circuit Bent Sonic Absurdity:
www.bogus-noise.co.uk
http://www.youtube.com/user/BogusNoise |
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