MCUmall EPROM BIOS Chip Burner Forum
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 Using The Enhanced/Dual power Willem Programmer
 Problems reading NMOS EPROMs
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ftvwdlt

3 Posts

Posted - 02/08/2017 :  07:43:13  Show Profile  Reply with Quote
Hi,

I'm using a dual powered Willem Programmer to read old EPROMs (M27128A, 27256).
Unfortunalety I get a lot of reading errors. Some days ago with a 27256 where I thought of a faulty IC, today a 27128 with the same problems.
Reading CMOS-EPROMs like 27C256 works.

As I read the power supply can be a problem. I use an external AC/DC adaptor instead of USB supply. On the powered IC on the willem board I can measure 4.88V between VCC and GND.

I also tried to change the timings without success.

Anyone with suggestions what could have gone wrong?

Thanks
Reply #1

anniel

332 Posts

Posted - 02/09/2017 :  03:51:02  Show Profile  Reply with Quote
Bit creep?
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Reply #2

ftvwdlt

3 Posts

Posted - 02/10/2017 :  00:01:39  Show Profile  Reply with Quote
Sorry, I'm not sure what bit creep means.
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Reply #3

anniel

332 Posts

Posted - 02/10/2017 :  04:30:17  Show Profile  Reply with Quote
In some old chips the MOS cells tend to slowly shift voltage values.
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Reply #4

emorysmith

USA
8 Posts

Posted - 02/10/2017 :  08:22:23  Show Profile  Reply with Quote
4.88V seems a bit low. The older chips draw more current and may be pulling your Vcc down.
I'm not familiar with the "dual powered" but my PCB60e is USB/External powered and I use a 12V 2A wall wart.
Does your board have a 7805 regulator? If so, does it get warm?
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Reply #5

emorysmith

USA
8 Posts

Posted - 02/10/2017 :  08:39:46  Show Profile  Reply with Quote
This may be of interest:
http://www.mcumall.com/forum/topic.asp?TOPIC_ID=1630
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Reply #6

anniel

332 Posts

Posted - 02/11/2017 :  06:44:55  Show Profile  Reply with Quote
Sorry, I am using a GQ4X, can't help you with the 7805.
When dealing with difficult chips I use an external variable power supply and isolate the voltage from the programmer to find the sweet spot.
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Reply #7

ftvwdlt

3 Posts

Posted - 02/17/2017 :  03:19:53  Show Profile  Reply with Quote
Today I took some time for it.

I took the bridge for 3V3 power and put an external 5V source on the EPROM supply.
This didn't take much time and did the job without modifications.

Thanks for helping!
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Reply #8

anniel

332 Posts

Posted - 02/17/2017 :  03:49:15  Show Profile  Reply with Quote
Good but there is no need for modifications. You can put a small V shaped piece of paper in the ZIF socket.
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Reply #9

supervizeur

26 Posts

Posted - 04/01/2017 :  12:55:58  Show Profile  Reply with Quote
Or a piece of Kapton tape folded in 4 sticky side in.
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Reply #10

anniel

332 Posts

Posted - 04/01/2017 :  16:21:44  Show Profile  Reply with Quote
Yes, that's also what I use but I suppose not everyone has Kapton on hand. Not that they shouldn't have some around.
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Reply #11

supervizeur

26 Posts

Posted - 04/11/2017 :  18:02:46  Show Profile  Reply with Quote
+1
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Reply #12

anniel

332 Posts

Posted - 04/15/2017 :  06:33:57  Show Profile  Reply with Quote
Talking about Kapton, I wonder why the cheap Chinese copies outgas that pungent smell.
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