Non-functional HP 33E

[quantumforce]

I have an HP 33E that isn't working properly. Here's a video:



As it shows, the display lights briefly with zeros after turning on, then flickers, displays some random characters, and dies.

Any suggestions what could be causing this? Is it a bad chip, or something I might be able to repair if I take the circuit apart?

[Steve Simpkin]

(05-12-2021 09:18 PM)quantumforce Wrote:  I have an HP 33E that isn't working properly. Here's a video:



As it shows, the display lights briefly with zeros after turning on, then flickers, displays some random characters, and dies.

Any suggestions what could be causing this? Is it a bad chip, or something I might be able to repair if I take the circuit apart?

If it is an early Spice model that did not have soldered ICs, it could be a bad connection. It could also be a damaged ACT IC caused by someone using the AC charger without a battery installed.
More info on Spice repairs.

https://www.hpmuseum.org/forum/thread-16...ight=Spice

https://www.hpmuseum.org/forum/thread-11...ight=Spice

https://www.hpmuseum.org/forum/thread-16...ight=Spice

[quantumforce]

(05-12-2021 11:26 PM)Steve Simpkin Wrote:  It could also be a damaged ACT IC caused by someone using the AC charger without a battery installed.

The ACT seems likely. The battery connector is damaged so the battery doesn't make electrical contact anymore. In the video it's running off just the AC charger. I didn't know that was damaging.

[AndiGer]

I think he tries to run the calculator from the charger, no? 9.9V ...

[Steve Simpkin]

(05-13-2021 06:19 AM)AndiGer Wrote:  I think he tries to run the calculator from the charger, no? 9.9V ...

After looking closer at the video I think you are right. It looks like he applied 9.9 VAC to the charger port, probably without good batteries installed. If so this probably destroyed at least the ACT chip. Another victim of HP's bare-bones charger design. He should have applied 2.5 VDC with the correct polarity to the battery posts for testing.

[PANAMATIK]

(05-12-2021 09:18 PM)quantumforce Wrote:  Any suggestions what could be causing this? Is it a bad chip, or something I might be able to repair if I take the circuit apart?

In the background there can be seen the HP-33E/C User manual. Chapter "Service and Maintenance AC Line Operation" says: "Note: Do not attempt to operate the calculator from an ac line with the battery pack removed". What the manual doesn't say: This will destroy the circuits inside.

Just Read The Instructions!

As the previous post said, use 2.5 VDC with the correct polarity to the battery posts for testing. If you are lucky the circuit has survived. Otherwise the only repair would be the SPICE LP.

Bernhard

[quantumforce]

Yes, I'm running off the 10V charger directly. The battery connector was broken off, so I'm sure that this was not the first time that was run without the battery in circuit. Sigh. Mia culpa.

I'm sure others have mentioned before how bloody stupid it is to have a removable battery that destroys your device if it is operated while removed. A small, non-threatening warning in Appendix A of the manual does not compensate for this design defect. Unfortunately my 1 year warranty has expired.

[aurelio]

(05-13-2021 07:58 PM)quantumforce Wrote:  Unfortunately my 1 year warranty has expired.

warranty?

[quantumforce]

Running from 2.5V off the battery contacts worked! The ACT is fine. I am thrilled. Now I just need to find some replacement for the battery.

I might try to fix the battery holder so it can take standard NiMH rechargables. Then I could ignore the 10V charger.

[PANAMATIK]

(05-13-2021 08:24 PM)quantumforce Wrote:  Running from 2.5V off the battery contacts worked! The ACT is fine. I am thrilled. ...

My Congratulations! It seems the SPICE calculators are more resilient than the "Woodstock's" to AC powering without battery. There are much more defective Woodstock calculators than SPICEs.

Bernhard

[Maximilian Hohmann]

Hello!

(05-13-2021 08:24 PM)quantumforce Wrote:  Now I just need to find some replacement for the battery.

Throw the original charger away (or at least keep it in a safe distance from the calculator) and get one of Mark Hoskins replacement batteries. They work perfectly well, I use them since many years in all sizes for each series of classic HP calculators. He also has a USB powered external charger for the battery packs.

Regards
Max

[PANAMATIK]

Another trap to avoid: Never try to insert normal AA accus, because they are too big and will crack the housing; use the smaller Flat Top AA NiMh accus.

Bernhard