Old Kingray Mast Head Amp Power Supply Replacement

[Gabriel486]

Ive got an old Kingray mast head amplifier power supply that is 22v AC 40mA and the new ones from Kingray are 17.5v AC 100mA model PSK08 would a 17.5v be ok, Ive also seen another Kingray at 14v DC 150mA, I dont know what the amp is on the mast yet but I'll look later its about the size of a cigarette packet

I have no signal at the moment so I'm looking at the power supply first, in the two pictures below if I get my multimeter do I test for 22v AC at the coax grounded shield wire at the clamp and the coax centre wire going to the mast head and then test if its getting 40mA at the same locations.

Ive had trouble getting a signal since updating the TV and moving the aerial to a different location outside so I understand Ive got to get a signal strength meter and if I can afford one a signal and quality meter, I'll look at the other possibilities like cable, wall socket, needing a booster or reducer, the amp box on the mast. I'm in a rural location so from my understanding the free to air digital will be using mostly UHF and when I get a cheap strength meter I'll be able to see if I'm getting at least 50dBuV.

I'm not sure if the pictures are going through so here is the link with postimage:

[mtv]

Plenty of 22VAC power supplies around.

However, given it's age, (that supply was from the 1980's) I highly recommend replacing the amp and supply.

Most new amps have LTE filtering.

65dBuV is the ideal signal level, BUT... most importantly is the signal quality.

If you have poor signal quality (eg: high BER) it won't matter how much signal level you have. In fact, too much signal is just as bad as not enough signal.

Antenna mounting location is very important if you are in a marginal signal area, as you need to obtain good signal quality at the antenna.

Amplifying a poor digital signal just gives you a 'louder' poor signal.

Many TV's can display signal meters but you need to see the screen whilst moving the antenna.

Meters with BER (signal quality) are expensive.

Yes, most regional TV is UHF.

Where are you located and what antenna are you using? If it's as old as the amp, it may also need updating.

[Gabriel486]

mtv im in Dargo Victoria I'm doing this for a friend so my replies are not as quick as I would like, I checked on his TV and it says its getting 100% signal and about 57% quality there is a picture but it has a pixelated screen I cleaned the contacts for the male and female connections for the box that plugs in to the aerial the one with a single coax cable and I looked at the mast amp its a Kingray MHU34G and I noticed there was a jumper on the right that was on when it should be off going by the options, on for 17.5 AC or 14 DC and off for 22v AC so I removed it but it is still the same, I tried upping the UHF gain but it was already to the max available, I checked the coax wire from the house and wall plate and the power supply is putting 20v AC to the mast amp so it isnt the cable or wall plate my guess now is it could be the mast amp or antenna position. I did notice at the power supply it was about 22v but it wasnt 40mA it was very low I cant remember at the moment but at the mast amp it was 20v and once again I should have wrote things down for the mA.



I dont know what the name of the antenna is but its the same one I had under my house

[mtv]

Going by the look of that amp, there's likely some shorts with all the crap in it.

At the very least, it needs to be cleaned up... both sides of the board and inspected for any corrosion.

The coax terminations need to be re-done... moisture has likely corroded the conductors, so you'll need to cut it back to where it's all shiny.

You would be better with an F type shielded amp.

The antenna in your pic is a phased array type, which is fine for UHF.

Where is the antenna pointing... to the main TX site at Mt Taylor? If yes, the antenna should be horizontal Eg: 90deg from the pic which shows it vertical.

There used to be a low-power (5W) retransmission site servicing Dargo on the Mt Thomson Track with vertical polarisation, but it's not listed any more on the transmitter list.

If you are getting pictures but pixelated, that's due to high BER (low signal quality).

You will need to relocate the antenna to a better position to raise the signal quality.

[Gabriel486]

Mtv I was able to get the picture on the tv perfect I was told by a local to remove the mast amp completely, before doing this I moved the aerial and made new coax wire for all connections and a new power supply but it was still the same so I have the amp at home with me to understand if its faulty or just not needed, I noticed the only electrolytic cap was 450uf in circuit in stead of 470uf but I guess if the tolerance is 20% it should be ok plus I tested it in circuit so it wasnt a great reading I will take it out if I have to later, the actual pcb board looks good there is no corrosion or broken traces, but one thing I found is when the old power supply was used at 22v AC the jumper for using 22v was around the wrong way so it was set to be using 17.5v/14v instead of 22v I dont know if the extra volts could of damaged anything yet. There is one thing I have to ask when I was removing the mast amp and touching the aerial I noticed a voltage to the touch on the actual aerial there was enough voltage there to make a tingle to my arms and fingers I'm sorry I cant remember if I unplugged the power supply at the time, I guess I didnt but an aerial with no power to it cant produce enough voltage from UHF to be noticeable to the touch right?

Ide like to know if the mast amp is working right how do I test if the mast amp is working properly, I have my old antenna to use as a test and my understanding is a multi meter cant be used to test if the UHF is working but I bought a cheap strength meter but it doesnt do quality strength

[mtv]

As I mentioned, too much signal can cause high BER just as bad as insufficient signal.

What signal level in dBuV is your reading without the amp?

Chances are it was overpowering, given it it a 34dB model, so taking the amp out of line may have brought the levels within the correct range.

Without accurate signal measurements, it's impossible to tell.

As for the electric shock, if the antenna was completely isolated from any equipment you should not get any sort of shock.

If antenna cabling has been run near mains cabling there can be an induced voltage present, or there can be an electrical earthing issue if the mast isn't grounded.

[Gabriel486]

I didnt check what dBuV after getting the TV to work I basically said its working and job finished he was happy, the mast wasnt earthed previously so we didnt change it and I didnt know to do this I will earth it to make sure and I'll make sure there is no more voltage to it now the amp and power supply are not connected. For now I am just curious to see if the amp box is working and if theres a way to test it with just a multi meter or a cheap bunnings signal strength meter, before I forget to say, thank you for your help mtv

[mtv]

You can check voltage from the power supply with a multimeter, but the only way to reliably test an amp is to test signals in and out with digital signal instrumentation.

You will get an 'indication' of increased signal level using a cheap meter, but it won't show you how it's performing regarding BER (Bit Error Ratio) and MER (Modulation Error Ratio).

It's a good outcome that you got it working.

Looking back on your posts, you said the TV showed 57% signal quality (again, it's only an 'indication' as it doesn't show actual BER/MER figures) but the 100% signal strength suggests the amp was too powerful, overloading the tuner and creating errors.

It would be interesting to know what figures the TV now shows with the amp and supply removed from the antenna.

[Gabriel486]

I agree about checking what the signal strength and quality is without the amp connected, I'm interested to see too now that you've mentioned it I will go back to his tv to see what it is, I tried turning down the UHF gain on the amp when it was connected but the picture was the same but the audio was ok. For now I have to convince him to let me borrow his Vast DSD 4121 satellite box as it too has not been working for a long time I have a satellite dish at home I just wanted to see if his LNB was faulty or if it was the F59 connector at the back but I would have to take it apart without him around to see if the connector needs re soldering