| Posted By
Dunric
on 2002-08-14
|  Bad TED chip?
How can I tell if it's the TED chip that's not working? I have two Plus/4's, one working, one not. The "functional" Plus/4 works fine, and you see the usual start up screen and can run software on it, blah blah blah. But the "non-functional" Plus/4 has the power light on but no screen display. At random moments, I can get a faint "white flash" horizontal line just briefly when I power it on, and then the usual black screen of death situation. I checked and then replaced the fuse, still black screened. I even took out the TED and reinserted it to no avail. The white "gooey" stuff used as a heat sink is still cold and gooey and should have provided the Plus/4 with adequate cooling for TED. The machine was in it's original packaging since late 1984. Not surprising, as a lot of Plus/4's I have found have been in mint or near-mint condition. Not sure if this is an "orphan" situation or people just had too many to sell and not enough buyers (because of the C64)?
Paul Panks
dunric@yahoo.com
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Posted By
JamesC
on 2002-08-15
| Defective Plus/4
Paul, this was discussed in the comp.sys.cbm newsgroup, in fact I think you brought it up.
First, swap power supplies. Plus/4 uses two different input voltages and you might have enough to power the case light but not enough to initialize the chips.
Second, swap the TEDs in your two Plus/4s to see if the problem stays with that one Plus/4 or if the problem follows the TED chip no matter which motherboard it's on.
If swapping TEDs doesn't work then swap the CPU (7501 and 8501 are compatiable with each other but nothing else... 7501 is original, 8501 is high-speed manufacturing process).
Verify that your monitor cable's RCA plugs are in the correct sockets on the back of the monitor. Using your 128 or the other Plus/4 can do this.
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