HT750 HT1250 No Power On

[SPARKS007]

Seems a common problem to the HT750/HT1250 series of radios in all bands. The power on process is rather complicated since it involves a lot more than the on-off switch supplying power to the various regulators. A simple RC circuit supplies an initial short supply of switched B+ which then powers the processors in the ASFIC and microcontroller which then in turn activates the switched B+ circuit through the ASFIC to an on condition, all within about 12 milli-seconds. 12 ms does not give enough time to trace problems. Since this seems to be a common problem ( I have 6 of all the same model right now, all at the same time exibiting this problem) so I was hoping that someone has figured this problem out. If so, I would certainly appreciate some insight. Also, I have yet to find the 38.4 KHz processor crystal shown in the service manual (FL401 - U409) - it is not where it is shown.

[com501]

After you turn the switch on, how much current is the radio drawing in idle, even though you think it never powered up?

Usually you are looking for a bad reference oscillator. If you have a small amount of idle current, look for the reference xtal and see if it is running......

[SPARKS007]

Thanks for the reply. It does have a small current drain although I did not measure it. The reference crystal does come on for the brief period that the initial RC timed circuit allows, also Vdda, Vddd, 5 volt supply, switched supply voltage, etc. So it seems related to the processor not booting up and allowing the ASFIC processor to activate the switched B+. The fustrating part is that I have seen at least 20 of these units with the same problem - or at least the same symptom. Every Motorola model possess a unique set of common failures, just wish I knew what this one is. Of course if it was the reference crystal it is not available through Motorola because it requires temperature compensation through the factory software. The price of factory flat rate repair is more than the value of the radio.

Since it seems to be a reoccuring problem I was hoping that someone else has also seen it and determined the cause. Thanks for your input.

[35echo]

Sparks,

The problem is probably the flashrom, especially if the radio is not lead-free. The older AT49LV001 series of flash chips
have a poor track record. A way to verify is to monitor the data and address pins for either a repeating pattern or tri-state logic levels.
If a repeating pattern is found the processor is not getting good data and is constantly asking for a repeat. If it looks like a tri-state logic level
there is a short or leak between pins on the flashchip usually. The two pins are trying to drive to opposite rails and that make it look like a tri-state signal. We replace the AT49LV001 series with the AT49BV040B chip which has a much better track record.

Another very rare problem is the eeprom. We have seen a couple of times where the processor tries to load the eeprom and fails. The radio does NOT show eeprom hardware failure or checksum failure. If you watch the eepron csx and data lines you will see a repeating pattern where the processor is stobing it.
This occurs after the bulk of the loading is done from the flashrom.

Regards,
Allen

[ovidiu]

35echo,
please tell me if you connect pin 9 reset AT49lv001, A18 AT49bv040 and pin 6 NC AT49lv001,A17 AT49bv040
Thanks,
Ovidiu

[35echo]

Ovidiu,

Those pins are connected to microprocessor pins 17(PG4) and 18(PG5) no mater which version of flashrom you are using.
If the micro does anything with these depends on the bootcode in the flashrom. This is one of the reasons you cannot just copy the bootcode from a 1MEG chip, shove it into a 4MEG chip and expect it to work. Not only is the structure of the bootcode different there are differences in the content also.

Regards,

Allen

[Martel]

35echo writes:

- We replace the AT49LV001 series with the AT49BV040B chip which has a much better track record.

But what about then ? The replacement flashROM wiill be new, so blank... Is it possible to re-flash an HT radio ?

And if so, what software / HEX will be required to ressuscitate the radio...

And finally, since the Flash is blank, Won't the power-on problem (12ms on then OFF) repeat itself ?

Thank you hor the help...

[com501]

Wouldn't flat rate be a simpler and more effective approach?

[35echo]

Martel,

We write the flashcode to the chips before we install them.
Also Motorolas flat rate on the pro series is way high. We get the flash chips in bulk for a low price.
It takes less than 5 minutes to create the file to write to flash chip and about 10 minutes to install them. Then its just
whatever other repairs are necessary. This goes for portables or mobiles.

Regards,
Allen

[CircleBat]

sometimes its Q400 that goes and causes no power onto the board.. or it can be U102 being blown due to water damage causing power rail to drop to zero volts.. Sometimes it can be the reference crystal but U407 can also be another the culprit by doing a shotgun approach.. for the flash rom, it can sometimes be that too as to what 35echo was saying..that expains alot why this radio doesn't power up.. where do you get the flashrom from? 35 echo? I've noticed that sometimes this radio doesn't recieve and caused by the flashrom.. I must admit this Motorola HT750 is a real shotgun radio to troubleshoot but at least can be repaired compared to the turbo..

[35echo]

Circlebat,

Look at the 16.8Mhz crystal test point. If it spikes up on the spectrum analyzer and then dies the 16.8 and Q400 are probably good. Apply 7.5Vdc to swb+ line if 16.8 stays up then start looking for a repeating data pattern or
a tri-state logic signal on the address and data lines between the flash and micro.

Our last purchase of flash chips was a 500ct batch from a supplier in Wiesbaden Germany. Our next may be a 1000ct short production run from atmel itself.

Regards,

Allen

[ihanna]

Thanks for the reply. It does have a small current drain although I did not measure it. The reference crystal does come on for the brief period that the initial RC timed circuit allows, also Vdda, Vddd, 5 volt supply, switched supply voltage, etc. So it seems related to the processor not booting up and allowing the ASFIC processor to activate the switched B+. The fustrating part is that I have seen at least 20 of these units with the same problem - or at least the same symptom. Every Motorola model possess a unique set of common failures, just wish I knew what this one is. Of course if it was the reference crystal it is not available through Motorola because it requires temperature compensation through the factory software. The price of factory flat rate repair is more than the value of the radio.

Since it seems to be a reoccuring problem I was hoping that someone else has also seen it and determined the cause. Thanks for your input.

I am also having that kind of problem, very similar to that, I just can't seem to find the cause. I've already asked a "genius" and said he knows all about it but unfortunately he can't. hoping somebody can determine the cause so we would know what to do. thanks in advance!