Tag Archives: repair

The baby is asleep, and the 6W tube amp is quiet…

It’s 12:11am, August 12, 2010, and I just gave up doing my College Physics to replace the first stage preamp cathode bypass resistor as noted in V1.3 schematic. I sure wish it wasn’t half past midnight :). I have it on 10° or less volume, and 45° EQ, give or take a degree. I’m just guessing. I really want to crank it up to see if the tone and distortion sounds better. 9-6-2010 – It does need some circuit tweaking. It doesn’t sound good to me after all.
Continue reading

Marshall JCM800 2×12 combo amp repair

Marshall Input JacksI took on a new and simple project today. A friend’s amp started Marshall Circuit Boardgoing on the fritz, and he was ready to give it to the doctor. I’m no doctor by education’s standards, but I love to take what is hurt and broken and make it work again. I derive a pile of joy from the challenge of diagnosis and even more enjoyment when the job is done.

The problem that was described to me was that the amp wasn’t acting normal. The beautiful sound was yucky, and it lacked the power that it once had. Yippeeee! Not in that the amp is busted, but the symptoms describe a simple problem. The output tubes are going out or are on the way out.

I took the amp home and turned it on. I let the heaters warm up, and I watched them as they began to glow. Almost immediately, heat began rising out. I touched my dry finger to the envelope of the output tubes; one was hot, and one was not. Boom. There’s the problem. One of the Electro-Harmonix 6550EH tube’s heaters was burned out.

Output tube Electro-Harmonix 6550EHThe only other problem that I found was that the amp’s low input didn’t work. Upon further inspection, someone soldered the ground wire to the wrong tab on the jack. The hot wire was correct, but the ground wire was not connected to the barrel ring. The jacks are very wobbly so I am going to replace those.

I called up my customer and let him know what was up. He would need two matched  output tubes and two input jacks. Most of the labor will be in the replacement of the jacks. Checking the bias should be fairly simple task, and replacing the tubes will only take a minute.

Car Remote/Clicker Stopped Working

Broken and disassembled remote/clickers

Broken and disassembled remote/clickers

This is a problem that my sister has endured for a couple of years. Her car remotes have stopped working twice. The first time they quit working I simply re-soldered the battery holder onto the PCB. That pretty much fixed it.

Her car is a Chevy Cobalt, and she’s had it for over 4 years. The clickers are also that old. The second time the clickers quit, I checked the battery holders, and they were fine. They still didn’t work so she resorted to using the actual key to open the doors. Every time she opened her car the alarm went off. This went on for over a year.

I had given up on the clickers until the dealership told them that the remotes needed to be reprogrammed at $150 dollars each. I told my sis that it was not possible for both clickers to quit at the same time like that. The inside workings of that clicker could only be erased with the proper program and hardware.

Just the other day I took the remotes/clickers back from her and checked them one more time. One battery holder came loose again so I re-soldered it back. I checked the voltage at the pins of the microcontroller in the remote, and everything seemed to be working.

She came over to my job and we tested the remote. The panic and trunk buttons worked, but the important ones didn’t. She prefers to have lock and unlock over anything else. I used my pocket knife to activate the lock and unlock pads on the PCB and they work so my conclusion is that the conductive pads on the rubber buttons have lost their effectiveness.

Remote/clicker with hot glued tin foil

Remote/clicker with hot glued tin foil

The fix is to hot-glue some tin foil to each rubber button to make the contact for her. This quick fix worked for both remotes. A little solder on the battery holder and 10 cents of hot glue and tin foil saved my sister $300!

*Edit* Hot glue didn’t last more than a day. The silicone buttons were still non-stick even with the application of a cleaning solution. This time I am trying out super glue gel. It seems to work much better.

A digital clock of mine gets an upgrade

Check out the new power plug!!!

Check out the new power plug!!!

Have you seen this post from July 1, 2008? How to make a digital clock: Picaxe

Well, the clock hasn’t work for a few months. When I plug it in and then unplug it,  it shows a few random letters. Then it stops doing anything. Well, I figured that the display driver was broke since I noted it acted quirky in the first article  almost two years ago. I was wrong.

It seems that we should always start at the wall and begin troubleshooting from there. Always. This is probably rule number 1. Well, it all boiled down to this: the original wall-wart shorted out and burned up. This leads us to the title.

Check out the new power plug. The original wall wart was a 6 volt output. I am now using a 9 volt output since the 7805 IC would prefer a little more voltage. I also did a current consumption test, and this circuit uses less tham 30mA. Now it can be unplugged and transported much easier.

Check out the new power plug!!!

Check out the new power plug!!!

My travels in repairing broken electronics (2)

Today I had an electronic gate brought to me that stopped working. Here’s the thirty minute way to figure and fix…

  1. The “customer” came in and asked me if I could fix a circuit board. I said, “I can definitely try, but I can’t make any promises.”
  2. I asked him what happened the day it quit working. He said. “I hooked the power up backwards, and the fuse blew. I put a new fuse in, and it blew, too. I imagine something else is blown.”
  3. Based on his testimony, I assume that something has caused a short across the positive and ground. I tested the circuit without power attached, and there was zero ohms between red and black.
  4. Continue reading