The modem board is toast ...

[Q] I have a Motorola SLR5700 that will not pass self test or boot. Unit powers on but halts with the following LED light pattern.

Bell Symbol - Green

TxA - Off

RxA - Green

TxB - Green

RxB - Green

Network - Green

Click - Off

EtherNet 1 Port - Orange LED, no activity when Enternet cable is connected.

CPS, RDAC and Tunner will not connect from PC to SLR5700.

Unit was operation prior to this fault. I do not know what occurred at site. Power supply does have 13.8 VDC on PA and Modem FRUs.

In additional to my fault description below when a USB cable is connected between the SLR5700 and PC, I do hear the beep sound indicating a device has been connected to a USB port.

Searching the internet led me to your site.  I have not tried Telnet or Webserver attempts to connect to the repeater.

What may have occurred at site is unknown. I did find a network hub that also did not power on.  No visible signs of lighting damage either on antenna feedline, AC power line, or Ethernet cabling.

Any guidance is appreciated.  I strongly suspect the Modem FRU is defective. Hence a depot repair or I purchase a Modem kit to attempt repairs on my own.

[A] I tend to agree that something is wrong with the modem board. You can send it in but it's just as easy to replace it yourself - there are only two caveats:

1) The repeater may be too old and there might not be a compatible replacement. The SLR5000 has undergone at least two major design changes. When ordering a replacement board, you will need to provide the TANAPA number of the repeater (it's on the serial number label) to check.

2) If a replacement FRU can be provided, it will most likely be on a software version that is newer than what was on the old modem board. This means that as part of the repair, you will need to perform a software upgrade to bring the power supply and PA up to the same firmware version. For this, the repeater will need to be covered by a software maintenance package. SLR repeaters sold after 2019 come with 5 years software maintenance included.

The repeater will need some alignment once the replacement model board is in: this will mostly be the reference oscillator and receiver front-end. The TX power should still be okay since this data is stored in the PA as far as I know. I don't know about the modulation (at least I can't remember that details right now). You probably can do most of this alignment using analogue test equipment.

As to what caused the failure, my money is on lightning damage: lightning can hit an adjacent structure and induce voltages in your tower or coax. Lightning damage is not always visible and can cause latent failures whereby the affected device can run normally for days or months before failing. It's also possible for lightning to affect some equipment on site while other equipment remains unaffected.

It's also possible for lightning to strike miles away and the transient comes down the power or data line to damage your equipment.

Another common mode of failure occurs when the tower is grounded; the equipment is grounded and the right antenna and EMP are used but all of these grounds are connected to different earth sources. When lightning strikes the tower for example, a potential difference develops between the tower and other site hardware. This voltage drop can be quite high and get inductively carried over to other cables and system.

To prevent or significantly reduce the probability of lightning damage at a communications site, a comprehensive approach involving site design, strike termination, grounding, bonding, and surge protection must be implemented. Here is a list of measures you can take, based on the Motorola R56 Standard.

Reducing the height at which coaxial cables leave the tower and enter the building reduces the voltage on the lines. The best practice is for lines to enter at a maximum height of around 600mm above the floor.

Placing the tower a minimum of 10m from the equipment shelter decreases the magnetic field coupled into the building, increases the inductance of the transmission lines (reducing energy transfer), and limits lightning energy propagating through the earth.

Wherever possible, replace metallic telecommunications and data lines with fibre-optic cables to isolate the equipment room from lightning energy and ground potential rise.

In areas where ice can build up, eliminate ice bridges by using a non-conductive slip-joint or physical air gap (minimum 100mm) between the cable/ice bridge and the tower or building to prevent lightning energy from being diverted toward the equipment room.

Install air terminals (lightning rods) at the highest points of the a mast or building to intercept lightning strikes before they can hit insulated building materials or sensitive equipment. Ensure that these air terminals extend a minimum of 25 cm above the tip of the antennas or objects they are intended to protect. 

For towers taller than 45m, side-mounted antennas become vulnerable to direct strikes and should be protected using horizontal lightning rods mounted just above and below the antenna.

Install buried ground rings encircling both the building and the tower, equipped with ground rods spaced every 3 to 5m to effectively disperse high-energy impulses into the earth. 

In high-lightning areas, use radial grounding conductors spreading outward from the tower. These divide the lightning strike current into segments, allowing for more effective dissipation away from the equipment building and minimizing tower "ringing".

Bond the outer shields of all coax and waveguide cables to the tower using weather-sealed ground kits. These must be installed near the antenna, at the bottom of the tower before the cables turn horizontally, and at intervals of every 20m in high-lightning areas.

Ensure all utilities and communications cables enter the facility in the same general area (a single-point entry window). Bond all equipment to a common Primary Bonding Bar (PBB) so that the electrical potential of all equipment rises and falls together during a strike, minimizing destructive current flows inside the building.

Interconnect all independent grounded media—including water pipes, gas lines, HVAC units, metal doors, and structural steel—to the lightning protection grounding system. This eliminates differences in potential and prevents lightning from arcing (side-flashing) between differently grounded systems.

Every electrically conductive point of entry into the site (AC power, telephone, LAN, control lines, RF, and tower lighting) must be equipped with a properly grounded Surge Protective Device (SPD).

Use a coordinated SPD setup. Install Type 1 or Type 2A/2B SPDs at the main electrical service entrance to handle massive surges, and install Type 3 point-of-use SPDs near sensitive or critical equipment (like emergency response dispatch consoles) to handle residual overvoltages.

Install coaxial RF SPDs (DC Block or DC Pass filters) on all RF transmission lines. These devices must be properly grounded within 600mm of where the cables enter the equipment room.