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Repair / Akai 1731W Reel 2 Reel Channel Rec Issue
« Last post by wblackledg on Today at 12:32:44 PM »

I picked up an Akai 1731W at an estate sale to day.

Almost everything works.

However, the left channel is the only one that you can record on.

Audio passes thru the right side, but it doesn't record. Overwriting previously recorded Audio works but When you do record, the right channel is just blank.

So its like the signal is making it out of the recorder and the unit is attempted to record, but no signal is making it to the tape head?


Follow the 2 small paste apetures underneath it as per the datasheet, for flowing a bit more solder in them, i have extended the pads for those holes out from the footprint and having a full paste density for that pad where it was outside the part, just fair warning this did spray a few solder balls loose on about 5% of my last run, reducing the paste apeture would likely have put me in the clear.
The circuit as such is fine. The upper side drivers are slow, yes, but that's not really important, they are being driven statically for direction control, only the lower side switches are PWMing.

On a related note: which motor will accept 64 kHz switching? My experience with normal PMDC motors is, that at switching frequencies above 3..4 kHz you'll have enormous losses in the motor, to the extent that it won't even turn.
Well, you should see what others have done for full-bridge servo drives.  I make a line of brush and brushless servo drives.  We normally run them at 50 KHz.  But, the brush drives keep the motor shorted between PWM on pulses, unless there is excessive current.  That allows the current to recirculate in the motor winding.  I have dead time designed into the drive circuits, to prevent a high and low-side transistor from being on at the same time.  One of the features of this is it prevents the body diode in the FETs from ever conducting.  Those diodes are hideously slow, taking microseconds to turn on with large forward voltages.

There are two common schemes of driving brush motors with full bridges.  One is called synchronous antiphase, where having the motor stand still is done by having the two bridge halves at opposite 50% duty cycle square waves.  This forces a triangle-wave current in the motor, and can lead to substantial heating.  The other scheme is a sign-magnitude PWM, which it sounds like you may be using.  If you allow the current to recirculate between the PWM on-times, the motor will not heat up much.

Are you sure the gain is that high?
Manufacturing & Assembly / Re: 3D PCB printer & printing cost ?
« Last post by Rerouter on Today at 12:24:37 PM »
the part i have never understood with these printers is why they go with the conductive ink approach, when for rapid prototyping, you generally want a copper wire, I always assumed they would get a 1 oz thick bit of wire, as its extruded coat one side in a UV setting epoxy then as its drawn along the board pulse a UV laser to cure the wire to the board,

You could combine this with a conventional printer if you didnt care about it being fibreglass, using a powder fusing printer for the core / prepeg. having a head pop over and spool copper in circles up the via or throughholes,
Beginners / Measuring voltage on metal chassis
« Last post by g.costanza on Today at 12:23:30 PM »
I’m in USA. Is it normal to measure 118v on the outer metal chassis of an audio amp, in reference to a wall outlet’s ground hole?
Beginners / Re: 5V Zener Regulated 5V from 240V mains, Why Blow Up?
« Last post by wasyoungonce on Today at 12:23:29 PM »
Please why are you not using an isolation step down transformer for safety.   Never run directly from mains.

Another fail is mains neutral in Australia is not earth....most house development us MEN (Main Earth Neutral) where earth is linked to neutral at one point in the power box.

You can control mains using a low pwr cct, its much safer so please consider this as direct mains circuits are very particular in components ratings.
It wasn't a problem with the older microwaves with the several kilo lump of iron and copper behind the control panel.  :) As has been suggested, use double sided tape, or Blutack, or similar.
Avoid the rubber based matting that's often sold for putting under items on shelves to stop them sliding around. It has a tendency to perish over time and stick to the shelf.   
Have you ever heard of a tensegrity mast?

You could build a tower of substantial height and extreme strength very easily. But if you do, its going to look like nothing else you've ever seen.

I have some friends who built one in the Bay Area around 20 years ago. Have to dig the photos out and scan them. Its mind blowing.
Dont watch too much bollywood movies, you'll got sucked up by sentimental crap..
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