Trim pots STILL don't work..... Why doesn't Radio Shack sell beer?

[ranchak]

Well, I thought I had found my problem with my Eighteen build. I thought I had the trannys in backwards, but they are in right. I still can't get the trim pots to reduce the voltage to the trannys. All solder joints look good. Even went back over them and resoldered everything. If I don't figure this out soon, there will be alot of stuff going to eBay!

[jrc4558]

Dont just check trimpots. When I was building mine I had same problem but it was because my electrolyticcaps were in backwards. Also, try to look for small bridges of copper between the pads. sometimes, sometimes...

[petemoore]

  Testing a trimpot is often as *easy as attaching DMM probes across it and measureing resistanceS as you adjust it.
  *provided there is no alternate current path through the circuit.

[Paul Perry (Frostwave)]

If Radio Shack did sell beer.... imagine it would be $5 a can, taste crap, and they would be out of stock anyway.
But as to the Eighten, it's pretty odd that NONE of the trimpots change the voltages!
What voltages are you seeing?
If the circuit is wired right, you should be able to see the resistance change across the trimpots a you tweak (withthe power off).
J201 pinout OK??

[billings]

$5 a pop, individually packaged, plastic+cardboard backing, hanging on the wall next to the batteries.

[redeffect]

Please dont give up. Maybe try stepping away from this for a day or 2. Sometimes, we get so wrapped up in something, a little break is all we need to reapproach it with a fresh outlook. That being said; unsolder a trimpot, and see if it really is good. Nothing is immune to failure. Till RS sells beer, just go next door to the deli, and buy some real beer Like Jimmy V said:" Dont give up. Dont EVER give up." You WILL make this work. All the best...
red

[jmusser]

If they sold beer.... Well, let's see. First of all they wouldn't know they did, because it wouldn't be next to the RC car or cell phone area. It would be be in a generic white can at $7.50, and would probably have a pull tab that pulled completely off the can! More than likely, you would be the one who found it, and If you decided to buy it, they would ask if you needed solder or batteries with it! Something's definitely wrong, if you're not seeing a voltage change on the transistor's collector while adjusting the trim pot. Either it's crap (which happens), or you have too low a value to make the difference in voltage you need for your application.

[Chuck]

A loose solder joint will do that too.
Resolder all the joints and look for bridges.
Chuck

[Meanderthal]

 When I built the Thunderchief the fet's squirmed like crazy! they would go from like 0.37v to 8.something with the tiniest little nudge... eventually I got somewhere in the neighborhood of 4.5 and it worked great. I heard around here somewhere that it works better if you start from the one closest to the output and work back to the one closest to the input... just a thought...

[lumpymusic]

I sometimes have squirrely circuitry that comes from using a lot
of sockets. Transistor leads don't fit well into SIP sized sockets,
for example. If I'm prototyping and seem to get varying results
by pushing on a component with a plastic tool, I suspect the
"tiny lead/big hole" problem.

I keep some standard value transistors and other components
around, pre-soldered to those little male pins made for db-9
style connectors.

Rat-Shack beer. Interesting idea. Might bring back the "macho male"
marketing draw. Maybe have Lattes and cappuccinos for the fems.

Lumpy

[ranchak]

Hey I found my problem. Just like most other problems, operator error. My trim pots are not 100K, they are 100R. No wonder this doesn't work. I guess you shouldn't drink a six pack BEFORE you place your order with Small Bear! Thanks for your help guys. Now I get to figure out why my TS808 clone doesn't work. I better go buy some brewskies before I get started on this one.