[time-nuts] SRS PRS10 repair

Brian Inglis Brian.Inglis at SystematicSw.ab.ca
Tue Aug 25 12:23:40 EDT 2015

You have too many 1s in your startup string compared to the expected "PRS_10\r".
If the MCU clock is not 10Mhz then the integrated UART rates will be off,
which should produce framing errors, but do UARTs still detect and systems
report these nowadays, or just pass along garbled data?
Otherwise, garbled data is most often a result of inadequate pin contact,
if the connectors are not seated properly, or the pins or sockets are loose
in their shells.
Age and rough treatment can have that effect.

"Internal hardware jumpers allow these pins to be configured as analog outputs
to monitor the lamp intensity and varactor voltage for complete compatibility
with the FRS."
Have you checked the jumpers in the manual Configuration Notes:
"Pin 4: TXD/PHOTO The default configuration uses this pin as an output for RS-232 data.
Many system parameters (including the lamp intensity) may be monitored via the RS-232
interface. The function of this pin may be changed to an analog monitor for the lamp
intensity by removing one resistor (R347) and installing a 10 kΩ resistor for another (R348)
on the microcontroller PCB."

On 2015-08-24 22:40, Brian M wrote:
> I tried through the weekend, double and triple checking wiring and setup.
> I've tried the following methods of getting serial comms working:
> PRS10 -> Arduino Uno (with processor bypassed) -> USB Host
> PRS10 -> Level Shifter -> BBB UART
> PRS10 -> MAX232 -> USB Serial adapter
> Shortly after power is applied to the PRS10, I do get a string of
> characters. Believe it should be the model information. Instead I get:
> wy+VPgy
> I guess the good news is that this output appears consistent with each
> power cycle of the device. And I'm getting the same results through all the
> hookup methods I've tried.
> My minicom settings are for software flow control at 9600 8N1 - from what
> the manual states, this should be the right settings. I've tried screen as
> well - and get the same text. I went crazy trying several other rates and
> setting combinations. No luck.
> Maybe I've missed something obvious.
> I agree that getting comms going to the MCU are going to be an important
> step. How do people address this type of problem? Scope the serial and try
> to decode by hand? The 10Mhz to the MCU looks OK on a scope. Are there
> further steps people try after that? If nothing else I think there's some
> interesting stuff to learn here. I also wouldn't mind tearing out the
> electronics, determining if the lamp is good, and attempt to build from
> there. I don't know the datecode for the unit, the PCB is marked with a
> datecode suggesting 2003? I don't have the full case. I'm trying to assess
> what are reasonable next steps. How do I determine if the MCU is healthy?
> If the MCU is fried, how do I determine if I just need to squeeze a new MCU
> board in there?
> Thanks! I appreciate the input so far!
> - Brian
> PS - after looking again at the signal on the scope, it does seem like it
> is 9600 baud. ~100µS per bit. The data out on the MCU itself looks like
> what I saw on the main connector.
> On Sat, Aug 22, 2015 at 2:04 PM Mike Cook <michael.cook at sfr.fr> wrote:
>>> Le 22 août 2015 à 03:40, Bob Camp <kb8tq at n1k.org> a écrit :
>>> Hi
>>> On any microprocessor based gizmo, getting the micro running (again) is
>>> generally priority number one. It sets everything up and gives you the
>> diagnostic
>>> info you need to go further. Garbled serial is better than none at all.
>> It suggests
>>> something short of a total MCU death spiral …
>>> Bob
>>>> On Aug 21, 2015, at 7:26 PM, Brian M <brayniac at gmail.com> wrote:
>>>> Dear list -
>>>> I have come into possession of a for parts prs 10. I'd like to try to
>>>> repair this device. What I've noticed so far. Serial is garbled. (Even
>> at
>>>> varying baud rates).
>>   You don’t say how you are connecting to the Rb. The manual states:
>> "RS-232 data is sent to the host on pin 4, received from the host on pin
>> 7. The baud rate is
>> fixed at 9600 baud, 8 bits, no parity, with 1 start and 1 stop bit. No DTR
>> or CTS controls are
>> used; rather, the XON/XOFF protocol has been implemented. The transmit
>> drive level is 0
>> and 5 V, not the +/-12 V normally associated with RS-232. These levels are
>> compatible with
>> most RS-232 line receivers, but does not require their use (a TTL inverter
>> may be used
>> instead), hence simplifies the interface when used inside an instrument at
>> the sacrifice of
>> degraded noise immunity over long lines."
>> So make sure that you adhere to that.
>>>> Lamp isn't lit.
>> What’s the date code. Early versions may be reaching EOL, though 20yrs id
>> quoted.
>>>> Doesn't look great. I'd like to know
>>>> if anybody else has wandered down this path. What are common failure
>> modes?
>>>> Anything match up with what I describe? Voltages to check would be
>> helpful.
>>>> The 10MHz out looked okay on a scope. Haven't gone further yet. I
>> suspect
>>>> the crystal is fine.
>>>> Thanks in advance. Happy hacking!
>>>> - Brian

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