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[kby] · 06-06-2019, 04:14 AM

I'm sure I've run across this either in this forum or the old one, but it's difficult to search symptoms that need more than a single description, so I'm hoping somone might be able to point me to the right thread(s).

I have a 25c that will power on and display "0.00" for a moment, then go blank. Bad ACT or something else? Thanks in advance.

BobVA · 06-07-2019, 03:22 AM

(06-06-2019 04:14 AM)[kby] Wrote: I have a 25c that will power on and display "0.00" for a moment, then go blank. Bad ACT or something else? Thanks in advance.

I wouldn't rule it our, but maybe you'll get lucky and it's just a power supply issue. Check the battery connector rivets and perhaps try gently sanding them where they contact the batteries. Also carefully check the batteries and spring in the pack and make sure they are also clean, making a good connection and are fully charged.

[kby] · (This post was last modified: 06-07-2019 05:13 AM by [kby].)

(06-07-2019 03:22 AM)BobVA Wrote:
(06-06-2019 04:14 AM)[kby] Wrote: I have a 25c that will power on and display "0.00" for a moment, then go blank. Bad ACT or something else? Thanks in advance.

I wouldn't rule it our, but maybe you'll get lucky and it's just a power supply issue. Check the battery connector rivets and perhaps try gently sanding them where they contact the batteries. Also carefully check the batteries and spring in the pack and make sure they are also clean, making a good connection and are fully charged.

Thanks! Good idea, but been there done that (or tried to…maybe will try again).

teenix · 06-07-2019, 07:08 AM

(06-06-2019 04:14 AM)[kby] Wrote: I'm sure I've run across this either in this forum or the old one, but it's difficult to search symptoms that need more than a single description, so I'm hoping somone might be able to point me to the right thread(s).

I have a 25c that will power on and display "0.00" for a moment, then go blank. Bad ACT or something else? Thanks in advance.

After showing "Error", does the display still go blank after a battery removal reset?

cheers

Tony

[kby] · 06-07-2019, 09:19 AM

(06-07-2019 07:08 AM)teenix Wrote:
(06-06-2019 04:14 AM)[kby] Wrote: I'm sure I've run across this either in this forum or the old one, but it's difficult to search symptoms that need more than a single description, so I'm hoping somone might be able to point me to the right thread(s).

I have a 25c that will power on and display "0.00" for a moment, then go blank. Bad ACT or something else? Thanks in advance.

After showing "Error", does the display still go blank after a battery removal reset?

cheers

Tony

This one actually never shows ”Error” now that I think about it. It actually isn’t always consistent on power on; sometimes blank, sometimes a stream of digits. Other times it shows 0.00 in run or 00 in PGRM mode (so does see the switch), but, regardless of the display, it only last for a second and the display goes blank. Usually switching off then on again immediately will give the same types of displays, but not always; sometimes it’s blank. Waiting and/or removing/replacing batteries will eventually bring it back to the point it was at before.

The “Error” message is only on the 29c.-kby

AndiGer · 06-07-2019, 04:14 PM

Maybe it is this article you are looking for?
https://www.hpmuseum.org/cgi-sys/cgiwrap...i?read=267

Searching this site also has some postings mention "resolder all contacts".
Don't search using the search function here but by google limited to site:hpmuseum.org

BobVA · (This post was last modified: 06-07-2019 04:34 PM by BobVA.)

I'd be suspicious of the ACT chip, which can malfunction in a surprising number of ways.

If you have some basic troubleshooting experience and the equipment, you might want to check the outputs of the power supply to rule that out. The HP-25 schematic
here has the necessary information.

[kby] · (This post was last modified: 06-16-2019 02:49 AM by [kby].)

(06-07-2019 04:14 PM)AndiGer Wrote: Maybe it is this article you are looking for?
https://www.hpmuseum.org/cgi-sys/cgiwrap...i?read=267

Searching this site also has some postings mention "resolder all contacts".
Don't search using the search function here but by google limited to site:hpmuseum.org

Thanks; no, that one I did "re-find" after reading it before; not the same symptom. I'll have to remember that about using Google; I know you've (or someone else has) mentioned it elsewhere before

[kby] · 06-07-2019, 05:06 PM

(06-07-2019 04:31 PM)BobVA Wrote: I'd be suspicious of the ACT chip, which can malfunction in a surprising number of ways.

If you have some basic troubleshooting experience and the equipment, you might want to check the outputs of the power supply to rule that out. The HP-25 schematic
here has the necessary information.

Power supply seems reasonable; I think(but should re-check as I might be confused with the 29c I'm also working on) that Phi 1 and Phi 2 look OK on the frequency. I'm learning (I think correctly?) that it's hard to get the peak-to-peak values out of a "true RMS" meter since the waveforms aren't sinusoidal—wondering if I'd be better back-calculating them from a cheaper "fake RMS" meter reading.

I'm also considering a 'scope, which I know is what I really need for this and other projects.

[kby] · 06-08-2019, 02:32 AM

(06-07-2019 04:31 PM)BobVA Wrote: I'd be suspicious of the ACT chip, which can malfunction in a surprising number of ways.

If you have some basic troubleshooting experience and the equipment, you might want to check the outputs of the power supply to rule that out. The HP-25 schematic
here has the necessary information.

Replacing the ACT didn’t change the symptoms. Found a disintegrating resistor, but replacing that didn’t change things either.

BobVA · 06-09-2019, 01:23 AM

(06-08-2019 02:32 AM)[kby] Wrote: Replacing the ACT didn’t change the symptoms. Found a disintegrating resistor, but replacing that didn’t change things either.

Power supply voltages are probably the next check, then. If the PSU is working it can be pulled down by a failed component elsewhere. (In this thread Alberto discusses needing to remove the RAM IC in his HP-25C before he could get correct voltages.)

[kby] · 06-09-2019, 07:05 PM

(06-09-2019 01:23 AM)BobVA Wrote:
(06-08-2019 02:32 AM)[kby] Wrote: Replacing the ACT didn’t change the symptoms. Found a disintegrating resistor, but replacing that didn’t change things either.

Power supply voltages are probably the next check, then. If the PSU is working it can be pulled down by a failed component elsewhere. (In this thread Alberto discusses needing to remove the RAM IC in his HP-25C before he could get correct voltages.)

I think I checked they were OK, but I need to re-check to make sure I’m not confused about whether I checked this one or the 29c I’m also dealing with.