Locked SY-41CL back to life

[JurgenRo]

Two month ago or so I tried to plug a non-existent ROM Image. This resulted in a display showing all @s, otherwise the machine was totally locked. Removed batteries for approx. 2 month - the machine appeared to be still locked.

Finally, I disassembled the machine to check contacts (I'm using a replacement flex PCB by Diego) and to get rid of the charge that was suspecious for the Trouble. Re-assembled the machine, switched it on and ... the trusty @s back in the display, the machine otherwise locked :-(

As I noticed that one of the screws did not catch, I fixed that and played with the pressure to the contacts applied by the screws. What I found is, that there is a small pressure range for which the machine is perfectly working! :-)

So, if you encounter a problem like this with your 41CL, chances are that you can fix it by gently loosing or tightening the screws.

All the Best,
Juergen

[Geoff Quickfall]

Those pesky pressure contacts!

A loose or bad contact during a write to flash can corrupt the software and result in a required reflashing for the whole calc.


Pm sent

[mfleming]

I've seen the same problem with a pair of calculators I'm trying to restore (41C & 41CV). Both had damaged flex circuits which I replaced, but both are still overly sensitive to applied pressure. The 41C has the early wound gold wire contacts while the other has the solid foam style of contact.

I've seen a description by someone who soldered 28 gauge wire between CPU board contacts and keyboard contacts, but I haven't seen any other suggested solutions. Does anyone know of a source for the vertically conductive strips, or can suggest some sort of low profile socketed connectors?

With 3D printing getting more available I wonder if some sort of snap-on connector could be fabricated?

Frustrating to have such a calculator almost working...
~Mark

[Geoff Quickfall]

Many discussions on this:

1. Frame work zebra stips
2. Non framework zebra strips
3. Wire wrapped
   

Wire wrap is best for CL conversion although my zebra working perfectly for years since beta testing. If sensitive then check screw posts for thread integrity.

Early 41C pre 1980 had nuts applying pressure to PCA for connection. Later these were removed and replaced with the rear shell lower screws compression method. The nuts were self tapping and not prone to reuses after service. They were replaced at HP service department with flat thick washers which then allowed the lower screws to take up the compression duty.

Geoff

[Dave Frederickson]

(01-09-2017 06:34 PM)mfleming Wrote:  Does anyone know of a source for the vertically conductive strips, or can suggest some sort of low profile socketed connectors?

Fujipoly is the mfg for the zebra connectors.
http://www.fujipoly.com/usa/products/zeb...ctors.html
I tried to get samples for repairing a 71B but was unsuccessful.

Dave

[mfleming]

Geoff Quickfall sez:

Quote:Wire wrap is best for CL conversion although my zebra working perfectly for years since beta testing. If sensitive then check screw posts for thread integrity.

I think I'll try the wirewrap approach for the 41C since its zebra shows a bit of green corrosion in places, and the lower posts are in bad shape. Asking the screws to just hold the case halves together is about all I can hope for...

I really do wish case assembly and electrical connectivity were orthogonal in HP design!
~Mark

[Monte Dalrymple]

Before I close up a CL conversion (and I've done this at least ten times) I've always cleaned the places where pressure is required for contact with DeOxit before putting the machine back together. I also try to "squish" the zebra connectors orthogonal to the direction of pressure to make sure that they have the best chance of actually being under pressure. This is especially important for the ones with foam-looking stuff in the middle. Also, if you have the foam ones, the plastic piece holding them in place wraps around the ends. This will be a problem because of several small SMT resistors that happen to be placed where they will hit the plastic fingers. So these wrap-around sections need to be cut off. I wasn't aware of this variant when I designed the CL board, or I would have tried to place things differently. With the other type of zebra connector, be very careful when cleaning them. It is easy to detach a wire or two and create a short between adjacent signals. this is very hard to see, at least with my aging eyes. I've only soldered one machine, using 30-gauge wire-wrap wire. And that was only because I had used the board for development and needed it outside of the calculator body.

Monte