HP8711B VNA power-up failed (alive now)

[mrf245]

hello
I jut picked up HP8711B VNA looks like very clear, but it power up failed.
Debug LEDs indicated "8" like picture shows below.
I tried to pulled up BOOT ROM, LED shows 8 with a dot and "HALT" LED is illuminating.
Referenced to CPU board schematic, use oscilloscopeto check bus, it looks like CPU is reading BOOT ROM continuously, and no other action.
Can anyone point out what I should do next?
Thanks very much   

[TheSteve]

I see no ram in the sockets - I thought it needed ram to boot.

[TK]

The sockets are for adding additional RAM and you need to set the correct DIP switches next to the sockets.  The CPU board has DRAM marked as U61 to U68 (The SIP chips).

CPU Board schematics (CLIP): http://www.ko4bb.com/manuals/24.3.150.247/HP_HP871x_network_analyzer_Other-A208712-60002CPU.pdf

[TheSteve]

I don't have mine anymore. I just know it only had 1 MB of ram even though there was ram in the sockets.

[TK]

I have the 8713B and it shows 4MB DRAM without any modules in the sockets.  If I add 4 SIMM modules, it shows 4MB DRAM and 4MB SIMM, for a total of 8MB RAM

[mrf245]

Thanks TK and Steve. SIMM RAM is not necessary for normal operation except BASIC options.
Seller said it worked fine before but one day it suddenly no power-up.
I checked battery its OK, and re-plug CPU in set as service manual noticed, nothing.
I also set switch beside SIMM socket, it switch on at "1MB" position before. After turn all switch off (set to up position), it still not working.

[Armadillo]

use oscilloscopeto check bus, it looks like CPU is reading BOOT ROM continuously, and no other action.
Can anyone point out what I should do next?
Thanks very much   

You should probe every bits of the Address and Data lines. Objective is to detect if one of the line is stuck.
After that, you proceed to the address decoders. Here is where analyser is useful. otherwise manual probe.
If there are electrolytics, the former may have changed leaky caps but left the ring of death on the boards.

Hope it helps.

[TK]

Do you see anything on the display?  My unit had a dead CRT module problem: https://www.eevblog.com/forum/testgear/hp-871xb-vna-crt-module-capacitor-identification-help/msg1239724/#msg1239724

Check the fuse on the CRT module.

[mrf245]

Do you see anything on the display?  My unit had a dead CRT module problem: https://www.eevblog.com/forum/testgear/hp-871xb-vna-crt-module-capacitor-identification-help/msg1239724/#msg1239724

Check the fuse on the CRT module.

Yes, CRT module is fine. Can you hear "beep" when your VNA power up? I have no heard on this one.

[TK]

Yes, I can hear "beep".

Error code 8 means one or more self-test failed.  I think you can find the error by looking at the schematics and following the traces from the diagnostics LEDs.

You can find all the schematics (CLIP) here: http://www.ko4bb.com/getsimple/index.php?id=manuals&dir=HP_Agilent/HP_871x_Network_Analyzer

[TK]

From the Service Manual

Error 8: Test number not used because test status LED powers up with his as default.  An "8" on the LED indicates the 68020 was unable to power up and execute basic instructions.

[mrf245]

From the Service Manual

Error 8: Test number not used because test status LED powers up with his as default.  An "8" on the LED indicates the 68020 was unable to power up and execute basic instructions.

Yes I consider it means CPU normal boot failed. Guess BOOT ROM is fine (no use programmer to ensure), maybe shared RAM or other nearby circuit? I will go on to check

[TK]

From the Service Manual

Error 8: Test number not used because test status LED powers up with his as default.  An "8" on the LED indicates the 68020 was unable to power up and execute basic instructions.

Yes I consider it means CPU normal boot failed. Guess BOOT ROM is fine (no use programmer to ensure), maybe shared RAM or other nearby circuit? I will go on to check

What the service manual suggests when you get error 8 is to change the microprocessor 68020.

[mrf245]

From the Service Manual

Error 8: Test number not used because test status LED powers up with his as default.  An "8" on the LED indicates the 68020 was unable to power up and execute basic instructions.

Yes I consider it means CPU normal boot failed. Guess BOOT ROM is fine (no use programmer to ensure), maybe shared RAM or other nearby circuit? I will go on to check

What the service manual suggests when you get error 8 is to change the microprocessor 68020.

Yes manual said replace 68020 or whole CPU board...This type of 68020 is not easy get from local market. I will try to check CPU and related circuit, or replace CPU if I get one.

[TheSteve]

I figure there is better odds the ram failed versus the processor.

[mrf245]

OK, I update some about repair job.
It's finished and working fine now.
In fact, not CPU board fault, it's failed in power supply.
+15V output is only +4V, and I found there is "pwr-fail"signal in module socket.(shows below)
Good module it output 5V, but this fail module output 0V.
I have no tracked where this signal goes into CPU systems, but I'm sure if this is low, it will halt whole CPU system from boot, maybe it's protect function, but it mistook me to check if CPU system was failed.
So it look like easy. Pull out power module, find +15V output zone, I found rectifier diode (FEP6DT) was shorted.
Purchased new one and replace it. Now 15V is normal. Whole 8711B run normally now.

[TheSteve]

Very nice! I hope the capacitors are ok, I've seen a few of these supplies with caps that leaked.