HP Forum Archive 06

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different cx guts Message #1 Posted by Miguel (Denver) on 17 June 2001, 3:56 p.m. So my 41 CX has been out of commission for a while (no problems with my 11c though) and I thought I would look for a repair service. I was pleased to find this forum and opened my cx to see if the posts were cracked... inside I found a monolithic PC board and quite intact posts. The s/n is 2830s21883. Is there any hope? thnx miguel

Re: different cx guts Message #2 Posted by Tony Duell on 17 June 2001, 4:18 p.m., in response to message #1 by Miguel (Denver) There are 2 basic types of construction for the HP41 series. The original type had a PCB with the keyboard on it, heat-staked to the cover. The display module was linked to the top end of this board by soldered connections. The chips (all pin-through-hole DIP packages) were mounted on a second board that was connected to the keyboard assembly by having a connector clamped between the logic board and the keyboard when the case was assembled. Finally a flexible PCB provided the battery contacts and module contacts -- it was folded round a plastic frame in the lower case, and pads on the flexible PCB were clamped against the keyboard PCB when the case was screwed together. The second type is called the 'halfnut'. It has one PCB with the keyboard contacts on it. On the other side there's a single surface-mount chip which is the CPU. The display driver bybrid also contains the RAM and (basic) ROM. The CX models have another PCB mounted on soldered posts across the back of the CPU -- this board contains the extended functions ROM, extended memory and time module (but I have been told that the ROM on the display driver is different between CX and other models too). The first type of construction suffers from bad contacts (often due to cracked screw posts). Also, the first type was designed to be repaired by HP to component level. The halfnut versions have many fewer contacts and generally don't suffer from contact trouble Offical repair, BTW, was limited to replacing the extra board (in the CX), or the complete top case if there was a logic fault. Still, the halfnuts do still have the flexible PCB for the battery/module contacts, so it's worth cleaning the contacts on that (and the pads it connects to on the keyboard), and squeezing the foam a little to improve matters. If that doesn't help, there's not a lot you can do without another machine to strip for parts in general.

Re: different cx guts Message #3 Posted by Miguel (Denver) on 17 June 2001, 8:43 p.m., in response to message #2 by Tony Duell Tony- thanx for the info mine is as described as the earlier design except it has 4? discrete caps ,3 diodes, and a single smt (Quad flat Pack) device. after removing the battery/module contact block I found the screw posts were fine but the back half screw bosses were cracked. The battery/module interconnect presses on the main pc with these screws...I will try glueing them and repost.

Re: different cx guts Message #4 Posted by Tony Duell on 18 June 2001, 2:18 p.m., in response to message #3 by Miguel (Denver) The older version has a _separate_ PCB with the chips on it. This PCB slots over front 2 posts and is connected to the keyboard by a connector that fits between them. Your machine sounds like a later (halfnut) version. The SMT chip is mounted directly on the large PCB that also is the keyboard (there is no second PCB with the chips on it that you can lift off). The discrete components sound right for a halfnut version, too. Oh yes, on the CX halfnut models, there's a little 'strip' of circuit board running across the machine, soldered to pins that are soldered to the main PCB. It doesn't lift off either. If it is a halfnut, you can bypass the battery connector/module connector flexible PCB for testing by connecting a 6V power supply (regulated!) to 2 points on the main PCB. The machine should then work, but obviously without any plug-in modules. If you have a regulated ('bench') power supply I can look up where to connect it to. Doing that would prove whether your chips were working properly or not.

Re: different cx guts Message #5 Posted by Miguel (Denver) on 20 June 2001, 1:19 p.m., in response to message #4 by Tony Duell thanx... I can trace the pwr lines on the batt/nodule block easily enough. I removed the contact block and found that the bosses on the rear case which support the screw heads are broken, I will post results when I get some CA on them.

Re: different cx guts -- repairing posts Message #6 Posted by Tony Duell on 20 June 2001, 5:23 p.m., in response to message #5 by Miguel (Denver) I assume 'CA' is Cyanoacrylate (iso-cyano acrylic hydro-copolymerising adhesive), commonly called superglue or crazy glue. Rather than use that, try and get some dichloromethane (methylene chloride), which is sold by good model shops in the UK under the name 'plastic weld'. It's a solvent for many thermoplastics (including HP calculator cases!), and you can use it to disolve a little of the plastic and weld it together. The result is a very strong joint. In general it's best to run a brush dipped in the plastic weld along the crack while holding the crack together -- it will be pulled into the crack by capillary action. You can also disolve some scrapings of the plastic in a little plastic weld and use it a a 'filler' -- e.g to mend stripped threads for self tapping screws.

Re: different cx guts -- repairing posts Message #7 Posted by Miguel(Denver) on 20 June 2001, 5:29 p.m., in response to message #6 by Tony Duell Tony see Hurray! above corrrect assumption w/re: to CA solvent weld would have been a better soln CA worked but caused slight whitening of nearby surfaces thnx Miguel

Note: not the posts Message #8 Posted by Miguel(Denver) on 20 June 2001, 5:37 p.m., in response to message #7 by Miguel(Denver) Note: the above described problem was not cracked mounting posts which recieve the threads, but rather the bosses on the back cover which the screws pass through and the heads bear on. The upper bosses are only visible after removing the battery/module contact block. miguel

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