Scullcom Hobby Electronics #9 - Time Electronics 404S & 404N DC Millivolt Source

[@Wally-H]

I wish I had a pound for every one of those darn things I repaired working at TE. The thumbnail switch assembly is called a Stolec, by the way. They get dirty in use - remove the end screws and carefully clean the PCB's then put it back together if you get inconsistent readings. We used to test the 404 electronic modules on an auto test bed - thousands of 'em! Your module was tested by my old mate Lewis Care. The circuit board does indeed extend into the potting compound. The compound is designed to make the module more stable, not to hide the electronics as some may think. As the unit was made in 1983, that module isn't original - it was replaced I would say, in the late 1980's as that was when Lewis worked there. The 'trimming resistors' were added when the Stolec was tested prior to being added to the finished unit. It was quite common for resistors to be required to make the required calibration on the auto test bed for that assembly.

[@scullcomhobbyelectronics1702]

Thanks John for your informative comments. Its always good to hear from someone who has been involved with the unit firsthand. Regards, Louis

[@freddybloggs9295]

Hello Louis, Thanks for the informative video. I had been looking for a user manual and schematic for the 404N. The video was helpful in understanding the operation the the device. I'd been thankful for your assistance. I have a faulty unit which functions as a voltage source although when turned on the 'Null Meter' flips full scale right regardless of switch position or of the pots. I've checked both switches for continuity across the contacts when operated, reseated the multiway connectors, and checked that pots function. I figure that the thumbwheel driven resistor voltage divider chain is not in circuit causing the null meter's deflection. Visual inspection of the boards does not reveal shorts or suspect joints. I'm wondering if you could help by sharing a schematic or if you have thoughts on the root cause of the fault.

[@andrewpusey6339]

Great video, I am considering picking one of these up if I can. On your calibration, should you be aiming for 999.90 not 999.99 etc ? Keep up the good work

[@martinda7446]

Loved watching this. Thanks.....Off to see your Micronta review now (I had a few of these). Subscribed of course.

[@scullcomhobbyelectronics1702]

+mart fart Thanks.

[@SoddingaboutSi]

Great, I have just bought a 404s and was wondering about calibration. Any idea what the non multi turn pot does? Meter calibration maybe?

[@scullcomhobbyelectronics1702]

Sorry for the delay in answering I missed your comment. I am not sure about the 10K non multi-turn pot. I need to have a closer look at the PCB next time I open the unit up. It may have something to do with the battery meter indicator but not sure.

[@zopilotesky]

Neat little gadgets!

[@armandine2]

Have one of these now on order - I'm maybe a little apprehensive regarding charging the unit

[@joaogama3498]

very good and claire explanation .thanks.

[@scullcomhobbyelectronics1702]

+João Gama Thanks.

[@MrMisa135]

Hi.... First of all thank you for such a good Video... Good explanation.............. I have a 404S millivolt source which for some reason stopped working...... the battery volt indicator does not show any indication with AA batteries but when i connect the charger it does indicates... Can you please tell me what could be the reason???

[@scullcomhobbyelectronics1702]

+Mohammed Asim I would recommend a few things to check: 1. Check that the long green connectors are seated correctly - these sometimes work loose or the contact pins are damaged (loose) or need cleaning. 2. Check for back contacts in the battery holders and twist battery cap for damage or bad contact. 3. Check the internal fuse and fuse holder clips.

[@MrMisa135]

+Scullcom Hobby Electronics .... problem was point no. 2...thank u very much....

[@scullcomhobbyelectronics1702]

+Mohammed Asim Glad to hear it was fixed.

[@АндрейПолетаев-щ6ъ]

Good video! But the most interesting, meter bridge is not shown(

[@scullcomhobbyelectronics1702]

Андрей Полетаев Thanks. Both units were very similar. May be I can show the internals of the meter bridge in another video.

[@GeorgeGraves]

Great video. Shame they potted the fun bits. Oh well.