Willem eprom programmer power supply

[jms2]

I have one of those cheap Willem eprom programmers, and whilst it is obviously crude it has worked fine for me. I have only ever used it to program 27128s and 27C256s.

Recently I have found that I can only program 27C256s. The reason seems to be that the external power supply input (as indicated by a yellow LED) does not seem to be fully working. If I plug in a USB cable, the LED glows brightly and I can program 27C256s. However, the voltage available from the USB cable is not sufficient for a 27128 (as I understand it), but if I plug in an external 9V or 12V adaptor the LED glows very weakly, the same in fact as if I had not plugged in anything at all. The voltage is definitely getting into the board from the socket, but I have not traced out where it goes from there.

My reading of this is that there must be some kind of voltage conversion device on the board which is broken for the 9V/12V input but OK for accepting 5V. Does this sound vaguely plausible, and/or repairable?

[sweh]

Depends on the 27128; I program mine via USB power with no problems

[jms2]

Hmm, maybe its the eproms then. I have tried several and all the 27128s behave the same. I thought the dimness of the yellow LED was a bit suspicious though.

[sweh]

Which model Willem do you have? Mine is a v5 board.

FWIW, the EPROMs I've successfully programmed are AM27128A which has Vpp 12.5V. Maybe you have older chips that require 21V?

[jms2]

Mine looks like a PCB4E. I think these roms do need the 21V programming voltage - at least, that's what I would have assumed.

[danielj]

I don't think you'll reliably get 21V out of a Willem.

[jms2]

Perhaps not... if I have to stick with 27c256s its not a disaster. Also, I wonder if jumper settings are a factor here.

[jms2]

I think I may have figured this out. There is an L7805CV voltage regulator on the board, which appeared to me to be standing up at a surprisingly vertical angle (usually they are laid flat). On touching it, I found that it felt alarmingly loose. I bent it slightly, at which point the dim LED sprang into life... and then the 7805 fell off altogether.

So I think this may be the issue!

[sweh]

and then the 7805 fell off altogether.

So I think this may be the issue!

[1024MAK]

So to clear this up...

The Willem Programmer is a design that has been implemented and manufactured by various companies. Hence there are various versions and variations of Willem programmers in the wild.

When using USB power, the lead should be short and a good quality type to minimise voltage loss (volt drop across the connectors and cable losses).

When using USB power, the +5V supply is directly derived from this. So EPROMs and EEPROMs that require a 6V VCC supply when verifying will only be run at whatever the USB supply can deliver (nominally 5V). To get the 12.5V, 13V, 21V or 25V programming voltage, a DC-DC converter is used. This uses an inductor. Unfortunately quite a lot of inexpensive Willem (and other USB powered) EPROM/EEPROM programmers can’t manage to maintain the required voltage at the current demanded by the EPROM. This is especially true for the older technology 21V and 25V EPROM chips. This is due to a combination of factors including a limited amount of power being available from the USB input, possibly poor design and possibly poor quality components.

When using the external power input, a conventional 7805 or similar voltage regulator is used to provide the +5V supply. In some cases, there is provision to increase its output voltage to about 6V for use when verifying. Obviously the 7805 is powered from the external DC supply. The same DC-DC converter is used, but as it now has a higher input voltage (recommended to be 9V to 12V), the available power from the PSU is greater, and it has less work to do to produce a 21V or 25V voltage, it’s significantly more reliable when programming the older technology EPROMs.

Generally speaking, older, smaller capacity EPROMs need the higher programming voltages. Newer, larger capacity EPROMs are often designed to be programmed using 12.5V.

CMOS versions (27C128, 27C256 etc) are also likely to only require a 12.5V programming voltage.

But it does depend on the manufacturer and exact type. Always check the relevant data sheet. Obviously where manufacturers have been helpful in that they print the programming voltage on the chip, then you have your answer and don’t have to search for the data sheet.

I hope this clarifies things.

Mark

[1024MAK]

I don't think you'll reliably get 21V out of a Willem.

You can if you use external power. I have a Willem and I have used it to blow 2764 and 27128 21V EPROMs without problems. But that does not mean that all Willem programmers will work, due to the variable quality of the components used in the DC-DC converter...

Mark

[jms2]

I hope this clarifies things.

It does, thanks. Your description of what should work, and what doesn't, matches my experiences very well. The real mystery was why the external power supply seemed not to be supplying any power whereas the USB input was, and I think the mechanical failure of the 7805 explains this.

I have a new one on order, so hopefully a quick bit of soldering will see this programmer back working again.

[JasonStonier]

Those 7805s can get quite hot, and this can fatigue-crack the solder joints so it's not an uncommon failure. I would put a heat sink on it when you do the replacement - doesn't have to be huge or sophisticated, a bit of angle aluminium door trim or something would be fine, held on with an M3 bolt and nut through the hole in the heat sink built into the chip.

[jms2]

Those 7805s can get quite hot, and this can fatigue-crack the solder joints so it's not an uncommon failure. I would put a heat sink on it when you do the replacement - doesn't have to be huge or sophisticated, a bit of angle aluminium door trim or something would be fine, held on with an M3 bolt and nut through the hole in the heat sink built into the chip.

That's a good point, but in this application the regulator doesn't get a chance to heat up actually. It only takes seconds to program a rom. In this case it wasn't the solder which failed, but the metal of the actual legs themselves, due to mechanical damage.

I have soldered in a replacement, and it has fixed the problem - the yellow LED glows brightly now when using the 12V power supply. And it programs 27128s successfully too, but before it would do that I realised there was another step that I needed to do:

The Willem software allows you to select the type of device and then shows a little picture of how to set the DIP switches plus some jumpers near the ZIF socket. This includes setting a jumper to the left of the DIP switch marked Vpp, which I assumed was the programming voltage selection. However, I noticed that the software doesn't tell you to move it when switching between 27128 and 27C256. So I reckon it doesn't control the programming voltage - the manual seems to suggest you only move it when programming some other kind of chip. To get 21V there are two jumpers to the right which you have to reconfigure - the software doesn't mention these, but a diagram in the manual shows what to do.

With these set to 21V it programs 27128s perfectly.