MCUmall EPROM BIOS Chip Burner Forum
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 True USB Willem Programmer (GQ-2X,3X,4X & GQ-4x4)
 GQ 4x4 with adapter and 27C800

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T O P I C    R E V I E W
MrTEE Posted - 12/14/2024 : 13:34:37
Hi!
Can anyone point me to instructions on jumpers, etc for a 27C800 in the GQ 4x4 programmer?

Recent purchase, I set it up and tried to read a 27C800 then verify.
(make sure everthing is setup)
I get verification errors
- latest firmware downloaded from the web, followed instructions
- adapter is properly seated, as is CHIP in adapter

I set the speed to slowest and still have verification errors (i.e. read contents of chip, then verify) seems like this should be 100% all of the time.
thankx
1   L A T E S T    R E P L I E S    (Newest First)
MrTEE Posted - 12/14/2024 : 13:39:16
BTW I also tried pin compatible MASK ROM chips and encounter the same random verification errors. (so I don't think this is so called "bit rot")
[Update]
changed Device from M27C800 to M27C800#2.
After that I was able to perform 10 read then verify cycles with no errors.
After looking at Device.txt, the difference between these two profiles is VCC which is 6.2V for MC27C800#2 vs VCC of 5.0 for MC27C800.
Putting a 'scope on VSS and VCC revealed
1/During a full verify power is cycled on/off to chip. Unexpected, as I would have expected supply voltage to be constant. (Sidebar)
2/ For Device MC27C800#2. (6.2V) measured voltage on scope was peak of 5.76V
3/ For Device MC27C800 (5V) measured voltage varied from 4.72 to 4.40V peaks.

Seems like the supply voltage is low/marginal
Is this expected behaviour?

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