These RF-5022 things is getting to me! So far, I know that the radio itself works, still need new batteries for the A6 (controller) card and the A20 head card. I have been waiting for their delivery for just about forever.

To review, the radio was working although it has no ability to save any stored data being the two memory batteries are dead but all modes were functioning normally. Turned it off and then back on and nothing, the head has a solid display of null characters and no function operate.

What I know.

Data travels from the radio to the head, can see the data stream, no data travels from the head to the radio.

The +28 volt source, +15, +5 and -12 volt power supplies in the head are all good. The memory backup battery has been removed.

U-16, the CPU clock is running at 9.21 MHz the reset bus from the Max 695 is LOW at pin 10 of U19 telling me that the reset is in the run and not hold position.

I can manually trip the master reset at E2 and see the reset status change to HIGH but it appears to make no difference.

The ALE, pin 33 of U-16 has its quarter clock signal on it.

U-17, the SRAM has +5 volts on VCC from the MAX 695, nothing when turned off because I still have not installed the battery.

Beyond pin 33 the output to the address decoder and memory chips I see no activity on any of the other pins, they are all held high. This includes AD0 to AD7, A8 to A15, RD/WR or any of the other ports on the CPU.

What I don’t know, the biggest problem with this is as always you never know what you don’t know until you know it.

Is the issue that the program that’s on the internal ROM in the CPU is not loading? maybe a bad CPU? It appears to me that the Internal/external ROM select on the CPU is hardwired to always boot from the external ROM/SRAM? And that’s started by an output from the CPU on pin 16, the imbedded program control line.

Speculation: after the reset the CPU reads internal code that pushes the imbedded program line to the appropriate state so the CPU loads the operating system from U-18 and that’s not happening.

The CPU, U-16 has a small PROM internal that contains the code for what happens on a reset or power up. IF the CPU, U-16 is bad, being that’s what the troubleshooting tree tells me is the boot code in the CPU unique to the Harris 5022? Or is it a generic code used for all 87C51FA devices?

Harris went thru a lot of work to make the controller (A6) and head (A20) have the ability to write new source code anytime, and not be restricted to always having to run the same code that’s hard wired from a ROM, is it possible that without the memory batteries by repeatedly turning on and off that I have overwritten or corrupted the code in the head and am now suffering the consequences?

The ability to overwrite the operating system (code) is built into the radio, how often did these radios write the code back to memory in normal operation?

The manual although in a limited way says that the controller (A6) polls the head and perhaps will push the operating system (code) to the head? Maybe the controller card I have is not doing that?

If that’s the case that none of the firmware, operating system or whatever you want to call the code is hard set into the radios that’s can be a huge problem in the future, because if you mess up the operating system you will need a way to replace it. I will have to look to see if you can push new firmware and how that’s done.

Will be interested in hearing other thought s about this.

Ray F/KA3EKH