Power Supply Board and stuff.

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Re: Power Supply Board

Postby Eric » Tue Jul 09, 2013 2:19 pm

I fixed the problem with the sound!
I replaced the LM358 with a fresh chip last night (The one I was using was salvaged from something else) and made sure to fill PIN 8's through-hole with a generous amount of solder to make sure that two traces going to it have a good connection. The volume levels are now perfect again!


But there's something else: >_<
The Tandy mod is causing the graphics on on the Exploring the IBM PCjr software to render incorrectly.
I'm getting some really glitchy stuff where it won't clear the screen and stuff. (Like the intro, the caterpillar and the printer sequences)

After a bit of troubleshooting and testing it with another 74s86 results in the same effects, but removing the modification does fix the problem.
Is this a usual side-effect for this software, or is there something I'm not doing right?

To answer any questions that might arise;
-I have not tested this with other software.
-I did remember to cut the trace that connects 74LS157 to 74LS273. (I didn't technically "cut" it, but I did desolder the legs to bend them up and cleanly removed the trace from the board. :p)
-I used thirty-gauge Kynar wire and .032 60-40 rosin core solder.
-Everything was wired correctly according to the guides.

What is causing this?

Brutman wrote:I have heard that the fuse in the brick is a common point of failure but I have never had one fail. I also know that breaking into a brick is not fun, as shown by your photo. Which kind of explains this abomination:


Yes - that is the innards of two bricks using a single cord to the wall. I presume it was used on a Racore/Rapport setup or something similar that needs two power supplies. It is really ugly and I've been scared to plug it in. Somebody had to work hard to get into two bricks, so I presume it happened when a fuse needed to be changed.

That thing is kind of intimidating. I wonder how hot the cord gets after a few hours of use. Was that housed in anything?

Brutman wrote:I know there are two major revisions of the power card - the short card putting out 33 watts and the long card putting out 45 watts. I don't know how many engineering changes there were that were not major like what you discovered.

I don't think the motherboard or anything else except they keyboard had more than one revision. The keyboard revision was not significant either - just mechanical. The innards are pretty much the same. But the power sidecar was definitely a cause of concern for IBM.

I've only had the 33 watt cards. Even this weird card is a short card.

I'll check its voltages later and and see if everything is fine-- Which I'm sure it is and that it wasn't the direct cause of that LM358 getting fried. That was probably caused by something that happened before I got that card, but I wasn't able to know until I put in the new card and powered it up.
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