HP/Symmetricom 58503A/Z3805A GPS Time and Frequency Reference Receiver Repair x2

[Ordinaryman1971]

Hi all,
Wanted to share my journey fixing two of HP/Symmetricom 58503A.
I have two of those units that are broken. Both of them have bad oscillators which are in my case  hp 10811-60212 but another member had 10811-60159 so I guess they are  interchangeable.
When I power the units up they voltage regulators powering the heaters are getting really hot and the units draws... 1.5A.
When the heaters are disconnected the current goes down to about .5A
First of the units fails the self test, fails also a oxco and efc.. That's what I see in SatStat before it fills with errors so it disables updates.
When I look at the log I see "invalid header" messages.

reply: -113,"Undefined header"
reply: -102,"Syntax error"
Sent: *IDN?
reply: -113,"Undefined header"

------------------------------- Receiver Status -------------------------------
SYNCHRONIZATION ........................................... [ Outputs Invalid ]
SmartClock Mode ___________________________   Reference Outputs _______________
   Locked                                     TFOM     9             FFOM     3
   Recovery                                   1PPS TI  --
   Holdover                                   HOLD THR 1.000 us
>> Power-up: OCXO warm-up                     Holdover Uncertainty ____________
                                              Predict  --
                                               
ACQUISITION .............................................. [ GPS 1PPS Invalid ]
Tracking: 0 ____   Not Tracking: 8 ________   Time ____________________________
                   PRN  El  Az                LOCL GPS 06:02:23 [?] 01 Jan 1998
                   * 1  -- ---                GPS 1PPS Invalid: not tracking
                   * 6  -- ---                ANT DLY  0 ns
                   * 9  -- ---                Position ________________________
                   *20  -- ---                MODE     Survey:      0% complete
                   *22  -- ---                         Suspended: track <4 sats
                   *24  -- ---                INIT LAT N  xx:03:04.414
                   *25  -- ---                INIT LON W  xx:53:37.933
                   *28  -- ---                INIT HGT         +194.28 m  (MSL)
ELEV MASK 10 deg   *attempting to track       
HEALTH MONITOR ...................................................... [ ERROR ]
Self Test: Err   Int Pwr: OK   Oven Pwr: OK   OCXO: Err  EFC: Err  GPS Rcv: OK


The second unit fails self test, oxco and gps receiver. The serial link is also going up and down, and often I'm getting.. no response from the unit.

Sent: *IDN?
reply: HEWLETT-PACKARD,Z3805A,3542A0xxxx,3543B-A


------------------------------- Receiver Status -------------------------------
 
SYNCHRONIZATION ........................................... [ Outputs Invalid ]
SmartClock Mode ___________________________   Reference Outputs _______________
   Locked to                                  TFOM     9             FFOM     3
   Recovery                                   1PPS TI  --
   Holdover                                   HOLD THR 1.000 us
>> Power-up: OCXO warm-up                     Holdover Uncertainty ____________
                                              Predict  --
                                               
ACQUISITION .......................................... [ GPS 1PPS CLK Invalid ]
Satellite Status __________________________   Time ____________________________
Tracking: 0        Not Tracking: 0            LOCL GPS 19:00:00 [?] -- --- ----
                                              1PPS CLK Invalid: not tracking
                                              ANT DLY  0 ns
                                              Position ________________________
                                              MODE     Survey:      0% complete
                                                       Suspended: no track data
                                              INIT LAT     0:00:00.000
                                              INIT LON     0:00:00.000
ELEV MASK  0 deg                              INIT HGT           +0.00 m  (MSL)
HEALTH MONITOR ...................................................... [ ERROR ]
Self Test: Err | Int Pwr: OK   Oven Pwr: OK   OCXO: Err  EFC: OK   GPS Rcv: Err

Wanted to ask if anybody has any experience fixing the oscillators and I guess heaters on them. When I connect the oscillators themselves... without the heaters they seem to be working.
Maybe somebody has those  hp10811-60159 OXCOs so I can just get one of them for testing.
Second, wanted to know what kind of gps receiver I should get to replace the faulty one or is there a way to fix it?
Third, what would be a problem with communication over serial... should I see and how to see what are the serial settings on those devices.
What would be a problem with sending commands. It does look like a firmware may be corrupted.
Anybody having copy of the firmware I may use?
There is command in SatStat to upgrade firmware but I have programmer and adapter, can burn them if needed.

[Ordinaryman1971]

After several tries I've got the response from the first unit:
Sent: *IDN?
reply: -113,"Undefined header"
Sent: *IDN?
reply: HEWLETT-PACKARD,58503A,0,3704-A
so... it's missing serial.....
Corupted FW?

[jfphp]

Are you sure that this old HPIB box knows the query IDN ? Most of my HP instruments don't respond to this question.

[Ordinaryman1971]

reply: HEWLETT-PACKARD,58503A,0,3704-A
reply: HEWLETT-PACKARD,Z3805A,3542A0xxxx,3543B-A

Communication is done over RS232 not GPIB, it also uses null modem cable.
You can see the response I hope... after several tries I've got the response from either machine.
So, yes it does work and it's a valid query.
I've started disassembly of one of the oscillators. Not sure how to remove the insulation from the inside...
It's very hard from aging... working on it.
So, the oscillators are marked as :10811-60212 one of them is LM9611, the other one LM9829. I guess those are the manufacturing dates.