Tempest missing +15v and +6.8v on main PCB

shirkle

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Any idea what would cause me to have just those two voltages way off? All others were almost exact.
I'm getting no video, and I know it's not a monitor problem because I'm using a modern PC monitor and the vectorvga board.
 
Any idea what would cause me to have just those two voltages way off? All others were almost exact.
I'm getting no video, and I know it's not a monitor problem because I'm using a modern PC monitor and the vectorvga board.


If I recall there is a 7815 and 7915 on the main board. Check the output on the 7815, I think its the pin all the way on the right.
 
The 7915 is showing (from L to R) 0.0, -24.0, -14.9
7815 is showing -24.0, 0.0, -1.4

The -1.4 is also what I get at the 15v test point.
 
"7815 is showing -24.0, 0.0, -1.4"
Are you sure its negative 24.0?
If you have a 7815 I would swap that out, most likely the problem.
 
I'm fairly sure. I actually remember checking it twice to make sure it said negative because it kind of surprised me.
Unfortunately, I don't have any of those handy..looks like I'll order a couple. What about the 7915? Those measured out negative also.
 
The 7915 is a negative regulator and should read negative. 78XX = pos reg. 79XX = neg reg.
Double check those readings again on the 7815, if your right there may be other problems on the board.
 
You are absolutely correct. It is positive. I just ran down there and retested it. I guess I confused it with the 7915. The -1.4 that it's putting out is actually negative, however. I assume that should actually be putting out a positive 15v.
 
You are absolutely correct. It is positive. I just ran down there and retested it. I guess I confused it with the 7915. The -1.4 that it's putting out is actually negative, however. I assume that should actually be putting out a positive 15v.

Correct, you have a bad regulator. Send me your address and I will get some to you in the morning.
 
Any idea what would cause me to have just those two voltages way off? All others were almost exact.
I'm getting no video, and I know it's not a monitor problem because I'm using a modern PC monitor and the vectorvga board.

Can I assume the 6.8VDC is at the 5VDC test lug? If so, unplug the motherboard before you do more damage. Having almost 7 volts running down the 5 volt rail is not good. Replace the 2N3055 on the A/R II board. If 6.8 volts is being tested elsewhere, disreguard above....but maybe tell where that reading was taken from.

Edward
 
I just went and grabbed a Tempest motherboard......I'll be damned, I never realized there was a 6.8V test lug.

Edward
 
OK. I got the new 7815, replaced it, and now I have those two missing voltages.

HOWEVER.....

The game still doesn't work. In fact, there is literally nothing on the screen and it doesn't pay blind or anything. It's completely unresponsive.
Where do we go from here???
Again, to clarify, this is definitely NOT a monitor issue.
 
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