Hi Mark,
You might not need to go to quite the same lengths as I'm going to. There isn't much space on my programmer for a physically larger inductor, so I was already leaning towards rebuilding the VPP supply on another board. Doing that would mean I could easily accommodate some extra circuitry.
In the first instance, you could try Luciano's modifications; see
Converting Willem Programmer PCB3b to PCB4.5, the section 'Improving converter DC-DC'.
As Luciano points out, the major problem is that tiny little 100uH bobbin inductor, it saturates at too low a current.
Before I start ripping bits off my programmer I'm going to lash up some circuitry to test the VPP supply. I think my findings will be the same as Luciano's, though. I found his page before my programmer arrived so haven't bothered trying to program the 27C1001 (27C010 equiv.) and larger devices I got it for; I just don't think it'll
work!
There was a version of the Willem programmer (4.1) which addressed the VPP supply problem by ditching the step-up converter and using an LM317 linear regulator. Of course, that means the programmer then has to be powered from a PSU producing a higher voltage than VPP is set to.
The PCB50 version is developed from 3.0, not 4.1 as one might expect. So the 'PCB50' inherits the VPP supply problems from the 3.0 (and some other problems which I'll address later in this thread.)
I wanted to retain the step-up converter, so I can still power the programmer with a 9V or 12V wall-wart, but gain a more robust VPP supply closer to that of the 4.1 version. Okay, now I guess I should stop waffling, build the new VPP supply and see if reality agrees with the LTSpice simulations
Kat