Stargate - power supply fail and error codes

[joeycuda]

So, here's where I am on the Stargate-

I replaced all of the IDC connectors on the harness with new Molex housings and trifurcon pins. The p/s board has been rebuilt with the Bob kit, all new headers (so solder joints not an issue), and even replaced the big filter capacitor with new. I did not replace the BR. I also replaced the housing and pins coming from the transformer. All fuses test ok out of circuit. I have reseated all socket chips.

I considered the boardset untested - pulled from a parts game, but very clean condition - no rot.

Power up - on p/s, the +5 and +12 check out good. Not getting -5. LED 3 is out.

What to check first? I'm assuming LED 3 corresponds to -5? Something the kit didn't replace?

On the ROM board, I get 1-3-2 error, then it goes into a 1-2 code. Rug pattern on screen.

I replaced the row 3, column 2 chip with new. No change, but the socket did seem a bit easy to push the chip into.

Any comments are appreciated! Can't wait to get her going (and finish a project!!)

 

[Dokert]

LED 3 is the -5vdc

Test the BR3 as I have outlined in my how to test bridge rectifiers video.

http://s291.photobucket.com/albums/ll282/dokert/Testing Video/?action=view&current=100_3099.mp4

 

[YellowDog]

A couple of other things to check for:
(1) make sure the fuse clips are tight. You wouldn't believe how often I see loose fuse clips causing problems. Also check for corrosion on the inside of the fuse clips.

(2) check the voltages coming out of the bridge rectifier (BR3, the little round one). The + output should read 0V (same as ground), the - output should read -11V or so. If not, it is likely that the bridge is bad. You used to be able to get them at Radio Shacks (1.0A 50V (link)).

(3) Check the voltage at the resistor next to LED3 (R14). The voltage should be -5V. If it is not, it is likely that the voltage regulator Q5 is bad.

ken

 

[joeycuda]

I will check these things tonight. In case the bridge rectifier is bad, I have some spares on hand. Thanks for the suggestions and I'll post a followup ASAP..

 

[joeycuda]

I still have no -5v/LED3

I checked BR3, per the video (great job, btw...) and it appears to check fine. Using the diode test, for the 4, I get between 535 and 555.

I then replaced the 7905, thinking it had to be it. No change.

The fuse holder clips seemed ok, but tarnished a bit. I replaced them with new. No change.

Still get no LED3, no -5v, and a 1-3-2 error, which I assume is partially because of the missing voltage.

What should I check next? Thanks..

 

[joeycuda]

(2) check the voltages coming out of the bridge rectifier (BR3, the little round one). The + output should read 0V (same as ground), the - output should read -11V or so. If not, it is likely that the bridge is bad. You used to be able to get them at Radio Shacks (1.0A 50V (link)).

ken

Just checked this.

I got 5.2 on the + output and -6 on the negative. Is this a typical failure point? Would it have likely taken out the voltage regulator?

Thanks..

 

[YellowDog]

If you look at the schematics of the power supply, the + lead coming off the bridge should be tied to ground. If that were true, you would be getting -11V which is about the differential you are getting. Try checking the traces to make sure that the + lead is tied to ground.

ken

 

[joeycuda]

Something is screwy here. It doesn't match up to the Stargate drawing set schematic, as I now realize the PCB is 5773-09679-00. This matches the one in the Robotron drawing set. Sorry for misleading anyone helping me!

I thought something was up earlier, as I couldn't see how F4 was related to -5v. 3rd WMS game, and I've yet to successfully repair one of these p/s boards. I know it's not THAT complicated, but I've sworn off switchers for the Williams games!

Looks like F1 goes with BR3/-5 on this. I replaced the tarnished fuse holders, new fuse. It doesn't look like the + leg of BR3 is tied to ground on this. I can see that there aren't that many components making up the -5 section. ARggggggggggh.

 

[Dokert]

There are only like 5 or 6 components in the -5vdc section. A very common problem is solder splash when replacing the tiny ass cap. Make sure that you have not bridged either of those two caps.

 

[YellowDog]

The -5V circuit is virtually identical between the Defender and the later power supply boards. If you check the schematics, the + leads in both cases are tied to ground.

ken

 

[joeycuda]

There are only like 5 or 6 components in the -5vdc section. A very common problem is solder splash when replacing the tiny ass cap. Make sure that you have not bridged either of those two caps.

No solder splash, good thinking though. I do think now.. C13 is like the only cap where I don't see a + or - screened on the PCB. I'm very careful when replacing caps, but to verify, I have the negative lead facing the inner area of the board, + facing outside edge.

Thanks for all this info. I've actually learned a good bit working on this.

 

[joeycuda]

I figured out why the + leg of the -5 BR wasn't tied to ground. The path to ground was supposed to go through one of the legs of the big radial cap, from bottom to top of board, thru hole. I removed the cap and there was no continuity from one side of the board to the other, as if the hole wasn't plated through. I added some solder to both sides, as well as the legs of the cap, so that when installed, it would all mush together and it did. Weird.

Still working though RAM errors. I got 1-3-1. The socket seemed flaky, so I replaced the socket with machine pin strips. Now, I get 1-3-8, even after replacing that chip with a new one.

 

[joeycuda]

I swapped the 3-1 and 3-2 chips around a couple of times, finally booted with "0", screen was garbled. I adjusted the monitor and it's now in attract mode... Almost there. Can't wait til it just needs new white buttons and an upper back door. Almost there.

 

[YellowDog]

Try recrimping the ribbon cable from the ROM cable to the MPU board. Frequently random RAM errors are caused by the wires working loose in the IDC connectors.

Here is a link to how to do this. (link) Just ignore ther first part unless you want to replace the ribbon cable (just skip down to the part about squeezing the connectors in a vise).

ken

 

[joeycuda]

Thanks! I will look into that ASAP.. I have replaced nearly every connector (crimp and housing) and header..doing all the preventive maint type things..

Actually, on the big RAM board, the double header for the interface board had some slight corrosion (mostly like white streaks) going under the headers. I removed that, cleaned it up with fine sandpaper, vinegar, alcohol, then doubled up .1 headers.

Replacing the ribbon cables is a good idea..

 

[joeycuda]

Just a follow up:

I ended up replacing both ribbon cables, getting them from Bob R. Game seems rock solid now. I believe Ken was right about the random errors and flakiness being caused by the old ribbon cable. I also replaced the interface board cable due to some very slight corrosion.

Seems reliable, for now!