MCUmall EPROM BIOS Chip Burner Forum
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 True USB Willem Programmer (GQ-2X,3X,4X & GQ-4x4)
 GQ-2X Voltage Drop Problem

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T O P I C    R E V I E W
jmullett Posted - 09/14/2007 : 15:44:34
I've got a number (~30 pcs) of TMS2764 I need to program. They have a program voltage vpp=21. I don't have any problems reading or verifying chips, but they will not program. I tested vpp with a volt meter and it is 21 volts during a write operation with no chip chip in the ZIF socket and drops to a miserable 11.8 volts with a chip. I am using an external 12v 1 amp power supply along side of the USB communications. and the few 12.5v and 12.7v chips I run across program fine.

I've read several posts that mention work arounds that bypass the switching circuit on the board for various versions of the programmers but no specifics or schematics especially ones related to the GQ-2X.

Can anyone give me some pointers? I'd really rather not purchase new eproms for this project.
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ZLM Posted - 09/15/2007 : 17:16:47
It seems the Vpp inductor has problem. You need to change the inductor of Vpp. Thanks to EZoSat.

Also, download the latest software to write the 27C64. It has Double-Write feature enabled on this chip.

For now, you may connect an external regulated 21V Vpp on T5 test point to boost the Vpp current.

Contact the support@mcumall.com for the inductors replacement you needed.
jmullett Posted - 09/15/2007 : 07:32:51
It does vary only slightly from chip to chip and the best result actually programmed about 10% of the EPROM.

Voltage during write on pin 28(vpp) was at 14.5V and at testpoit T5 it dropped to 16.3V during the write operation. It looks like I'm going to shell out the dough for CMOS chips.

quote:
Originally posted by ZLM

Did you try to change any other TMS2764? I just wondering if that particular chip been broken.

The 11.8V is too low to program a 21V Vpp chip. Something wrong. The TMS2764(21V vpp) in the verified list.

Also, check the T5 test point voltage when programming that chip. The T5 is located just beside 7805 regulator.
ZLM Posted - 09/14/2007 : 22:42:50
Did you try to change any other TMS2764? I just wondering if that particular chip been broken.

The 11.8V is too low to program a 21V Vpp chip. Something wrong. The TMS2764(21V vpp) in the verified list.

Also, check the T5 test point voltage when programming that chip. The T5 is located just beside 7805 regulator.

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