Correct SCELBI Power Connectors Added

I just added the correct SCELBI power connector to my reproduction. Note that this was the factory setup. Back in the day, some people integrated power supplies right into the chassis, rather than using an external power supply. The plug is a 86CP4 and the socket is a 78S4. These days, they are kind of scarce. In this case, scarcity equates to price, as they are about 9 dollars each. Check inventory at alliedelec.com for 78S4 and at tedss.com for 86CP4.

Here are some images.

SCELBI Power External

SCELBI Power External

You put the plug in the chassis so the cable coming from the power supply doesn’t have exposed pins.

Inside Power Wiring

Inside Power Wiring

The SCELBI manual says put +5 on pin 1, ground on pins 2 & 3, and -9 on pin 4. SCELI assembly directions have you position 1 and 4 at the top of the chassis. This makes wiring to the backplane pretty clean. The slip rings that are used to hold these connectors onto the panel are a pain to get on – be patient and don’t expect the rings to seat perfectly. I chose to connect the I/O port grounds directly to the incoming ground wire, rather than wire back to the backplane. Now I’m thinking I should have run both ground wires to the backplane, rather than join them together and run 1 wire to the backplane. I used 18 gauge wire, so it probably doesn’t matter.

Plugged In

Plugged In

The socket and plugs are keyed, in that two of the pins (positions 1 and 4) are larger than the other two. However, I think if you weren’t paying attention, you could plug this in far enough to make contact and cause problems. Be careful when plugging this unit in.

I have used electrical tape to protect the exposed terminals on the cable coming from the power supply. I need to pick up some of the hoods that are designed to cover these connectors. SCLEBI used gray clad multi-conductor cabling back in the day. I think it is still available, but like many SCELBI components, it is pretty expensive.

This process took me a couple of hours. Take your time to get things right and avoid costly mistakes.

Next up – getting the TTY interface built up and checked out. Other than schematics, and parts placement, we don’t have documentation for that board, so it might take a while.

On Arron Hernandez and the Patriots…

This is one of my rare (I think) rants.

In case you didn’t know, New England Patriot football star Arron Hernandez was recently arrested for murdering an acquaintance.

On sports radio and in other media outlets around the Boston area, there is steady stream of analysis about what happened and could it have been prevented, or at least did the Patriots knowingly, or should they have known that they hired a thug in order to better their football team.

In my mind, this is an open and shut case – anyone in a major business doing any hiring, besides doing interviews, will be required to do background checks, before the hiring takes place. This should include reference checks with credible individuals familiar with the candidate. I’m sure that in the top ranks of pro and college football, the Patriots, with a little do-diligence could have determined that Arron was not a good person. This should have been enough to steer them away from this thug. In fact, other teams did determine this, and passed on him. That the Patriots have a track record of bringing in problem players such as Corey Dillon, Randy Moss, Albert Haynesworth, should only go to show that their hiring practices are very suspect.

Winning is important in the NFL, so important that hiring decisions are routinely made that would never happen in a “normal” business. Think about it, if you were a Patriot employee, would you want to be around such characters as Corey Dillon, Randy Moss, Albert Haynesworth and Arron Hernandez on a daily basis. The Patriots are not the only ones at fault here, many, if not most teams have hired thugs over the years. One example, being recent Superbowl MVP, Ray Lewis. I personally think the NFL should smarten up and try to hire only people with outstanding character. Sure, they might miss out on some talent, and make some mistakes along the way, but if everyone is doing their best to weed out the bad apples, then it shouldn’t be a big issue. Anyway, if you were running a unbelievably successful business, would you hire a thug, if he potentially might earn you a few more dollars. Or would you do the right thing for the community and your employees, who have to work with this person on a daily basis and stay away?

I’m all for giving people the chances that they merit, but there is no excuse for a top notch organization knowingly and repeatedly hiring bad apples and then acting surprised when something goes wrong.

Subwoofer Repair

Background: I purchased a home theater system back in the 90s. The first subwoofer was a Definative Technology unit. It lasted about 18 months before failing. It was repaired under factory warentee. 18 months later, it failed again. It was just out of warentee, but Definative Technology was nice enough to repair it again. Sure enough, 18 months later it failed again. I made a quick attempt to repair, but when I didn’t see any obvious failure, gave up on it, and gave it away.

It was replaced was a slightly larger Outlaw Audio subwoofer, a few years back. A couple of weeks ago, the amp on this replacement failed with a blown fuse. Initially, I replaced the fuse, power came on momentarily, but the fuse soon blew, again. I decided to see what the Amp looked like, to see if there was any obvious component replacement that would fix it. Disassembly was easy, and I found the Amp was made up of three boards. There were no obvious component failures on any of the boards.

Since it was blowing fuses, I guessed that the problem was on the first board, which was a switch mode power supply, with Indigo and Bash logos. All components were through hole, with no custom parts, so I figured it would be repairable. Testing components with a diode tester and ohm meter revealed only possible issues with one of the two power FETs. I decided to order some replacements.

After the new FETs arrived, I replaced the suspect one and put everything back together. To my dismay, but not surprise, the fuse blew again. Clearly some other problem caused the FET to blow. I now devised a primitive ESR tester, and checked the caps, but they all tested as good. Continuing my investigation, I took a control daughterboard off the main board and tested each component, some by pulling, so I could test out of circuit. In particular there is a part type that I never heard of, before. This is a DIAC. I pulled it, found the specs, and devised a test fixture and it also looked good. Finally the lone transistor on the daughter card broke off from it’s leads. This was very strange as the daughter card did not experience any especially rough handling. Could it have been already broken from the stress of operation in the subwoofer environment, and my light handling just finished the job?

Since I could find no other problems, I figured I’d replace it and the two power FETs and see what happened. After replacement and reassembly, so far the subwoofer is performing like new, so I think that the problem was vibration induced failure of the MPSa92 transistor on the power supply daughter card.

Since my experience with subwoofer amps is that they have very poor reliability, I am very happy to have found a way to fix this one, at least this one time.