SP50 almost dead

arlojanis · Post by **arlojanis** » Tue Jan 17, 2006 1:47 pm

I have a UHF 10 channel SP50 that appears to be dead. No turn on beep. No led for rx or tx. A very, very low hiss with speaker to ear. Cannot read or write. 16.8 and 7.9488 oscillators are working. Any suggestions?

arlojanis · Post by **arlojanis** » Thu Jan 19, 2006 6:46 am

Post by **wavetar** » Thu Jan 19, 2006 7:56 am

My first thought would have been the oscillators, but you say they are fine. How did you determine that? Are you just verifying a signal, or are you able to measure actual frequency? I've seen cases where they have drifted enough off frequency to cause the radio to go dead (5KHz or more).

Otherwise I'd suspect the microprocessor, assuming your proper DC voltages appear to be where they should be.

Todd

arlojanis · Post by **arlojanis** » Thu Jan 19, 2006 8:19 am

To check oscillators, I attach a scope probe to antenna input on service monitor. I set monitor to crystal frequency. Then, I hold probe near crystal or touch can.

Tony Soprano · Post by **Tony Soprano** » Thu Jan 19, 2006 9:37 am

arlojanis wrote:To check oscillators, I attach a scope probe to antenna input on service monitor. I set monitor to crystal frequency. Then, I hold probe near crystal or touch can.

Works for me. This one's got me too.

If the clocks are working and regulated voltages are where they should be, my money's on the synthesizer/VCO section.

Post by **wavetar** » Thu Jan 19, 2006 10:04 am

Tony Soprano wrote:my money's on the synthesizer/VCO section.

I would think he should still be able to read/write with RSS if that were the case.

Todd

Tony Soprano · Post by **Tony Soprano** » Thu Jan 19, 2006 10:57 am

This one had me interested, so I cracked the manual, after first blowing the dust off

According to the book, the synthesizer must provide a stable 2.1 MHz output. The AFIC must see this output before it allows the microprocessor to complete the power-up. When the condition is satisfied, the micro P assumes control and allows the software initialization to begin, and subsequent power-up alert.

Places to check would now be pin 11 of U201 synthesizer for the 2.1 MHz signal, and check the reset line status of the micro P at pin 43. It's safe to assume that the AFIC and synthesizer are in control of the radio until all voltage and clock signals are present.

Post by **wavetar** » Thu Jan 19, 2006 11:59 am

Yeah, the dust is thick on mine too...I had assumed with the separate 7.9488MHz clock crystal, the micro wouldn't be dependant on the VCO for a signal as it is for some other radio models...guess I was wrong on that.

Good tips for troubleshooting.