MSF5000 just died. HELP!

[Jay G.]

HELP!! UHF 100w programmable unit., using a Scomm 7K controller (yes, i know its for ham use).

We had a utility failure. Generator kicked in and then went out when utility came back on. I dont know what caused the utility failure, other then it was a very large area failure.
Repeater has power, the REPEATER part is working fine. I think it might be something with the PA. When I key up, it blinks every light dealing with the PA on the reepater. You hear it clicking, but thats it. No output at all. Power supply voltage out is 15.6volts. Too high?

HELP!!!!

Thanks!

[d119]

Seems a bit high on the power supply.

Try backing the transmitter power output control down a little bit and see if it normalizes, with the higher voltage the repeater might be overdriving the PA.

It wouldn't be bad to just go through it and realign the entire station (including power supply). Hopefully you've a service manual?

[Will]

Power supply voltage out is 15.6volts. Too high?

HELP!!!! Thanks!

No, 16 volts at no or light loading is good. Spec is 13 to 16.3 volts, full load / no load.

Check the 9.6 regulated voltages on the main chassis.

[Doug]

As strange as it sounds could you give us a little more information. Is the station using internal filtering or external duplexers. I have a strange feeling that the noise you are hearing is the circulator in the amplifier folding back or shutting things down.
Doug

[bernie]

My two bits worth:
The voltages mentioned are fine providing you do not have the battery charging option.
These boards can fail in very un predictable ways. If no battery is installed set to 14.5 volts not 13.8 used for float charge.
These regulators, there are many versions mostly not documented, have a very slow recovery time.
A failing filter cap or regulator in the power supply can also cause the controller to reset on key up.
If the PA current momentarily draw drops the supply below 11 volts the MPU will go into a reset.

First, you need to use a watt meter to see if you have power out of the transmitter.
If there is little or no output from the PA there could be an internal failure.
Turn the power set control full CCW, key the station, slowly increase the power to rated output, 55W for a factory duplexed station. Be very careful to use the proper tool. Look in the hole to see what fits. This is because during manufacture they used what ever part was delivered that morning: slot, hex, square etc. If the screw driver touches ground the power will drop to minimum. Re key.
No output, connect watt meter to input cable of PA. There should be some point on the power set control where you see at least 9 watts.

We are now to the part of the trouble shooting tree that determines that you need a radio tech to continue.

The triple circulator is particularly troublesome.
The internal solder joints burn, causing the load resistors as well as other components to burn.
It is often possible to re solder the burnt joints restoring use of the circulator.
Some people by pass the defective internal circulator, I prefer an external circulator if a replacement internal circulator is not available.
I have also seen defective solder on the power interconnect board, as well as shorted 47uf Tantalum caps.
The associated metering resistor will be "exploded"
Very rarely a transistor module fails. Repairs are limited to replacing shorted caps.
If you have a burnt PA module, the balancing resistor on the output micro strip may also be burnt open.
It is possible to replace the predriver module with a Driver/Output module.

The output should not change with input voltage variations.
The IPA is on a regulated supply, its output is controlled by the power control circuit on the UNIBOARD, which is controlled by a power detector on the output of the PA power combiner. (the Grey cable)
Reflected power is indirectly detected via thermistors in the circulator, as well as PA heat sink temp.
Should the input satisfy requirements for over temp the power control drops the output to a preset minimum level.