Base Station Repair
This two way radio base station was brought in for repair by a customer with the fault being described as ‘dead’.
It is a VHF High Band model operating in the 160 to 175 Mhz frequency band and made by Tait Electronics in New Zealand. Given its about 20 years old, the radio is in very good condition and is a testament to the build quality of these units.
A quick check with a volt meter showed no output from the power supply which should produce 13.8 volts. Checking on the transformer secondary output showed 24 volts at the bridge rectifier.
Power Supply Module Removed From Rack
A visual inspection showed no signs of component failure or evidence of overheating etc. Measuring the semiconductors showed all appeared okay so time to power up the pcb.
The regulator board was connected to a DC power supply set at 24 volts DC so measurements could be taken.
A replacement PWM chip was fitted and the board powered up again.
A final check of the transmitter and receiver on the test set to ensure all is well.
A good clean output signal with no harmonics.
I wonder if it will last another 20 years???
This article was prepared for you by Ian Corry who lives near Lancaster in the UK. He is the owner of a sound and communications company supplying public address equipment and radio communication systems to events throughout the country. He has over 30 years experience in the supply, installation and maintenance of analogue and digital radio systems.
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You may check on his previous repair article below:
https://jestineyong.com/jedia-jpa-480cp-amplifier-repair-protection-mode-problem/
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Robert Calk Jr.
April 6, 2019 at 12:54 pm
Good job, Ian! Thanks for sharing the repair with us.
Yogesh Panchal
April 6, 2019 at 3:03 pm
Good Job! Sir,
Ian Corry
April 9, 2019 at 5:36 am
Glad you found it interesting Yogesh.
Ian Corry
April 9, 2019 at 5:35 am
Many thanks Robert..
Albert van Bemmelen
April 6, 2019 at 2:50 pm
Great job Ian! Maybe better switch off your room TL lights next time when taking snapshots of your scope screen to avoid seeing the reflecting light bars? I also would like to add a nice Spectrum Analyzer to my test equipment but as bandwidth and frequencies go up sadly also the pricetags do. To see if a matching service manual on Elektrotanya existed I typed in "Tait T800" and got a TAIT T800 SM service manual. Also a power supply unit with 13.8V DC output but with another 3525 controller used. Probably the Tait guys changed their previous design to newer versions. The same 144 page manual also speaks about the T800 programming software originally called BasePROG and PGM800. But although the manual is also about the T800 series to power base stations it is about the T807/808 power units for 50W and 100W base stations.
Robert Calk Jr.
April 7, 2019 at 5:56 am
Hi Albert,
I also can't wait till I can afford a nice Spectrum Analyzer! My new Siglent has FFT, but that isn't as good as a good Spectrum Analyzer. But it is better than nothing.
Albert van Bemmelen
April 8, 2019 at 2:11 pm
What is the maximum bandwidth and highest frequency that your new Siglent scope is able to show in FFT mode Robert?
Robert Calk Jr.
April 8, 2019 at 7:41 pm
It is a SDS1204X-E, 200MHz. It has two 1GSa/s ADC's, one for channels 1 & 2, and one for channels 3 & 4, with 1Mpts.
Albert van Bemmelen
April 9, 2019 at 2:30 pm
Okay, thanks Robert. I guess that in real-time its highest frequency that can be seen in FFT would be around (or halve) of 200 Mhz?
Albert van Bemmelen
April 9, 2019 at 2:38 pm
Okay, thanks Robert. I guess that in real-time its highest frequency that can be seen in FFT would be around (or half) of 200 Mhz?
Robert Calk Jr.
April 10, 2019 at 1:49 pm
No, the scope regularly sees 14Mpts, but only 1Mpts in FFT. But I am pretty sure it still shows 200MHz in FFT also.
Ian Corry
April 9, 2019 at 5:59 am
Thanks Albert. I'm pleased you found it interesting. Sorry about the lighting, unfortunately if I switch off the lighting, I have to put the whole workshop into darkness... and I've got some staff frightened of the dark!! 🙂
You are correct in that Tait manufactured many variants of their products and high power transmitters were common as they supplied countries like America and Australia. This model was a cross over as it were.. it used eproms to hold the channel data but required the file to be first written in the Tait PGM software, then transferred to a standalone eprom programmer for burning.
How times have changed. I hope you get your Spectrum Analyser, they certainly make things easier.
Mark
April 6, 2019 at 3:49 pm
Hey Ian,
Thanks for a detailed and comprehensive repair
Ian Corry
April 9, 2019 at 6:00 am
Thanks for your comments Mark. Glad you found it of interest.
Parasuraman Subramanian
April 7, 2019 at 10:34 pm
Excellent effort there! Pinning down the problem and solving it professionally is a rarity now-a-days! This is a new device for me! I learnt a few things from this article! Many thanks for sharing!
Ian Corry
April 9, 2019 at 6:05 am
Thanks for the post Parasuraman.. for you to say that you learned something new here is very pleasing for me. It just goes to show that we never stop learning!
Humberto
April 10, 2019 at 11:59 pm
Interesting repair. Another device saved from the dump