Andeen-Hagerling 2500A Capacitance Bridge   - Page 1
Forum section: electronics / general

author: maxamp
author_rank: Contributor
timestamp: September 16, 2025, 02:28:44 pm
content: Has anyone recovered the 6 digit pass code from an Andeen-Hagerling 2500A Capacitance Bridge? Its required for calibration. If so how did you do it?I contacted Andeen-Hagerling so far they just asked for the serial number."Entry of three bad passcodes in a row will cause all further passcodes to be rejected until power-on occurs." So brute force trial and error would require many power cycles.I was thinking maybe it could be read from an EPROM chipbut I haven't opened it up yet.

author: maxamp
author_rank: Contributor
timestamp: September 16, 2025, 04:35:40 pm
content: The manual shows an executioner if I open it up and don't reassemble it properly.https://manuals.repeater-builder.com/te-files/MISCELLANEOUS/ANDEEN-HAGERLING%202500A%20Operation.pdf

author: maxamp
author_rank: Contributor
timestamp: September 16, 2025, 10:38:26 pm
content: CPU is on top and capacitors on the bottom.

author: maxamp
author_rank: Contributor
timestamp: September 16, 2025, 10:41:17 pm
content: Some more close ups.

author: maxamp
author_rank: Contributor
timestamp: September 16, 2025, 10:57:25 pm
content: Here is the diagrams from the manual if you are wondering what is what.

author: Dr. Frank
author_rank: Super Contributor
timestamp: September 17, 2025, 07:52:39 am
content: do you have the schematics as well, and could you please upload the complete manuals to ko4bb.com?THX Frank

author: Phaseseeker
author_rank: Regular Contributor
timestamp: September 17, 2025, 08:51:34 am
content: If you have a dump of the firmware ROMs it might be possibile to find out where the password is stored in the EEPROM, but if the manufacturer can provide you said code it's way easier...

author: coromonadalix
author_rank: Super Contributor
timestamp: September 17, 2025, 08:54:07 am
content: i would have said to backup every eeprom in there ... just in caseif they asked the serial and you provided one normally they should have answered on the same call ?

author: krasimir.k
author_rank: Contributor
timestamp: September 17, 2025, 02:01:35 pm
content: HiYou can try with 65C02-Tool:https://github.com/Nectivio/65C02-ToolI never try it, but it allows to sniff the traffic between the CPU and RAM/ROM/EEPROM once you enter the passcode.Also it can be used as EEPROM reader.Kind Regards

author: Jacques
author_rank: Contributor
timestamp: September 17, 2025, 03:40:08 pm
content: Quote from: maxamp on September 16, 2025, 10:38:26 pmWhat's with that massive bank of Coto reed relays?

author: Hydron
author_rank: Super Contributor
timestamp: September 17, 2025, 04:14:16 pm
content: Probably for connecting the reference capacitors to the right taps of the ratio transformer

author: maxamp
author_rank: Contributor
timestamp: September 18, 2025, 05:34:09 am
content: QuoteNo schematics.I tried to upload to ko4bb.com but the Upload applet and FTP failed.You can find it here:https://manuals.repeater-builder.com/te-files/MISCELLANEOUS/ANDEEN-HAGERLING%202500A%20Operation.pdfQuoteI sent them an email with the serial number after they asked for them. They still haven't replied. I could send them a reminder email.QuoteQuoteLooking though the manual relays are also used to:-Zeroing-Apply a DC Bias Voltage-"The two most significant decades (RD's) use reed relays that directly switch voltages from the main ratio transformer to reference capacitors A and B. These two decades are identical except that the reference capacitors differ by a factor of ten from each other."

author: maxamp
author_rank: Contributor
timestamp: September 20, 2025, 02:19:35 am
content: A reminder email did the trick. Andeen-Hagerling send me the passcodes.

author: Jacques
author_rank: Contributor
timestamp: September 28, 2025, 12:20:34 pm
content: Quote from: maxamp on September 18, 2025, 05:34:09 amFor applying a DC bias voltage it seems a tad overkill, no? That is, I would expect something like a microvolt of thermal EMF to have a negligible effect when bias voltages are typically a few volts or higher. What am I missing?