Northeast Electronics TTS-28 Telephone Multimeter - Repair & Testing - PICTURES

[CarsonReidDavis]

I recently picked up a Northeast Electronics Corp Model TTS-28 multimeter/telephone tester. It has a metal case and included some decent probes. It set me back $28.50 USD. I haven't been able to find much information on this meter online. Let me know if you know anything!

It has a neat mechanical feature on the door that turns the meter off when you close the case.

It has the following functions, some of which I am unfamiliar with:

• DBM 900ohm Term.
• TEL SET
• DBM BRDG
• VAC
• METER SHORT
• VDC
• MA DC
• OHMS

So far, the repair has consisted of replacing the 3 batteries. It seems that it took a weird axial 9 volt battery with very similar plugs to a modern 9 volt. However I had to replace these with a modern adapter. It also took two 1.5 volt As which I replaced with some 1.2 volt rechargeables.

The probes are making bad contact, and I need to see if there is a good way to repair them. I'm not sure how to tell if they can be sanded or need to be replated or some other repair.

I have included two albums that have very detailed descriptions of my process:

• Repair: https://imgur.com/a/aLeLxwv
• Testing: https://imgur.com/a/VJ3kkOU

I haven't tested any of the telephone functions yet. Advice is welcome.

[CarsonReidDavis]

I've added to the testing album. It now includes:

• Volts DC
• Volts AC
• mA DC
• Resistance

All these functions seem reasonably accurate. Resistance is the most accurate.

I'm still trying to figure out the telephone stuff:

• DBM BRDG
• METER SHORT
• TEL SET
• DBM 900ohm TERM

[edpalmer42]

I'm still trying to figure out the telephone stuff:

• DBM BRDG
• METER SHORT
• TEL SET
• DBM 900ohm TERM

DBM BRDG = dBm Bridged.  The meter is calibrated on the assumption that it's measuring across a circuit that is already terminated.  It isn't explicitly stated, but the circuit impedance is probably 900 ohms.  This is the standard impedance for a subscriber line.

METER SHORT is just what it says.  It puts a short across the meter.  This helps reduce the sometimes violent motion of the meter pointer when the meter is being transported.  Sensitive meters can be damaged when they're being tossed around in the back of an installer's truck.  Hold the unit in your hands and twist it from side to side along the needle's axis.  Do it with the switch on METER SHORT and on any other position.  The motion of the needle should be much less on METER SHORT.

TEL SET = Telephone Set.  Connect a test phone to the Tel Set terminals.  Set the meter to TEL SET.  This connects the input terminals to the TEL SET terminals.  Dial the test number, then turn the dial to the 150 MA position to measure the current in the line.  Based on the known line characteristics you can get an idea if the line has some bad connections.  You can also see if the current is unstable which also indicates problems on the line.  Line current should be greater than 23 ma.  If you're right next to the telephone office, it might be as high as 125 ma. or so.

DBM 900ohm TERM = dBm with a 900 ohm termination.  Same as DBM BRDG except the meter provides the termination.

Regarding the batteries, I've never used a TTS-28, but 9V feels like it's too low.  If you replace the 9V battery with a variable power supply, how high can you set the voltage and still get it to zero?

Ed

[Cyberdragon]

No it's definately 9V. Vintage 9V batteries came in either axial or radial (modern style) connections. My pocket sig-gen has the same mod.

A company called Excell Battery makes odd and vintage battery types. Even tube B batteries and stuff (definatly going to check them out). NOTE: They are modern chemistry though and SUPER EXPENSIVE.

Here's your 9V type if you want to go sort of authentic.
http://www.batteriesinaflash.com/exell-high-output-ho226-lithium-manganese-dioxide-9v-battery-neda-1600

EDIT: Screw direct from their website, elsewhere is cheaper and not often out of stock.
https://mapleleafbattery.com/?product=exell-226l-lithium-manganese-dioxide-9v-battery-neda-1600-pp4

[edpalmer42]

No it's definately 9V. Vintage 9V batteries came in either axial or radial (modern style) connections. My pocket sig-gen has the same mod.

A company called Excell Battery makes odd and vintage battery types. Even tube B batteries and stuff (definatly going to check them out). NOTE: They are modern chemistry though and SUPER EXPENSIVE.

Here's your 9V type if you want to go sort of authentic.
http://www.batteriesinaflash.com/exell-high-output-ho226-lithium-manganese-dioxide-9v-battery-neda-1600

EDIT: Screw direct from their website, elsewhere is cheaper and not often out of stock.
https://mapleleafbattery.com/?product=exell-226l-lithium-manganese-dioxide-9v-battery-neda-1600-pp4

The battery holder doesn't look like it was designed for a round cell.  But who knows whether either of the holders is original.

I looked in an old catalog and they list the standard 9V connector as "min. snap".  There were other batteries listed as "snap" which had voltages of 6, 9, 12 and higher.  The 9V 226 battery, listed as 'snap', is 1" dia x 1-15/16" long.  The 12V 228 battery, also listed as 'snap', is 1" dia. x 2-7/16" long.  Notice that the standard 9V battery doesn't actually fit in the holder.  My ruler says that the body is about 1-3/4".  That means the 226 won't fit either since it's longer than the standard 9V.  See the problem?

Now, this is all rather academic.  The standard 9V battery works, it's cheap, and it can be made to fit the holder so that's probably the best solution.  The test I suggested would determine what voltage the circuit was designed for, but it would be more for interest than any practical value.

Ed

[Cyberdragon]

There were square axial 9Vs, but they were quite rare and I don't know the type number.

EDIT: Similar to the square 22.5V batteries.