|
Hello there!
My microwave counter is faulty. Time ago, it stops counting sometimes. Nowadays, it counts sometimes. I'm talking about 500 MHz to 18 GHz input. Always shows zeros in the display.
Anybody knows about this fault? The front end sensor wears? It is a pity, I heard about this model that the N connector input is sensitive above 5 dBm (I always have an attenuator attached) and I don't remember put more power than that, but...
Thanks to everybody who answer me :)
|
The 500 MHz - 18 GHz input is the tricky part of the 5342A. I happen to own 2, plus a parts mule in my cellar. The high input range uses HP custom built circuits making repair uncool at best, impossible at worst unless you find a parts mule.
Wilko
|
Must spend some time reading about the principles of operation. In the past, switching int/ext 10 meg source bring back the counting. Now that doesn't work. I'll pull from that thread first, just in case if there's a problem with freq reference.
I'll report here my conclusions and tests.
R.
|
One of mine (running from an external ref) would fail because the
internal ref was too far off to lock to the external (GPS-derived)
one - adjusted the internal ref slightly and all was well. Also
IIRC, the external ref needed to be around +10dBm?
On 21/04/2024 18:36, RubenRubio wrote:
toggle quoted message
Show quoted text
Must spend some time reading about the principles of operation. In
the past, switching int/ext 10 meg source bring back the counting.
Now that doesn't work. I'll pull from that thread first, just in
case if there's a problem with freq reference.
I'll report here my conclusions and tests.
R.
|
Does selecting the selftest display 75 000 000 ?
Without a reliable 10 MHz clock int or ext the CPU does not run. Essentially nothing works properly.
The switch for int/ext has been known to become unreliable.
Wilko
|
And yes, it needs a rather 'stiff' 10 MHz ext ref, I think I feed mine 12 dBm or so (subtract some coax attenuation though)
Wilko
|
Alright guys, I'll check that first. It also seems to me that there is a problem with the frequency reference.?I didn't know that the processor itself depended so much on the time base, but seeing how it has behaved other times, I'll check that and the int/ext switch.
Thank you ;)
|
PD: self-check doesn't show 75000000, only zeros
|
Just to be sure: I mean the self test you initiate with <SHIFT> 1
Wilko
|
|
|
Remarkable to mention that the input 2 works fine, with both internal and external freq references.
Internal opt 001 oven it's now adjusted to be closest possible to the gpsdo phase.
Still don't get that 75000000 with self check, I'll read the service manual about.
R.
|
PD: service manual is pure gold. I found this thread to pull ...
|
Hope that the microprocessor board is not fault, nor the U1 sampler, which is made of unobtainium. I will check synths and loops today...
|
The microprocessor board is the lesser of your potential problems. Tricky is that the 3 ROM version of that board uses mask ROMs. There are no pin-equivalent EPROMs for those. I went down a rabbit hole with one of my 5342A, assuming that a ROM was faulty. In the end it wasn't.
Worth checking is the dipswitch on the microprocessor board. It is used to enable signature analysis mode. I found stories from people who had a bad switch, obviously that prevents the firmware from running correctly. I replaced the switch in mine, just because.
Wilko
|
Hi,
Yes, the CPU board uses common parts, it is totally repairable. You can actually power up the board outside the unit for easy repair. I had one with faulty ROM, just as I got around using an adapter board to replace it with 2716 EPROMs, I found a replacement CPU board on eBay. I wrote about it on my blog:
Szabolcs
Wilko Bulte via <wkb= [email protected]> ezt írta (id?pont: 2024. ápr. 23., K, 11:14):
The microprocessor board is the lesser of your potential problems. Tricky is that the 3 ROM version of that board uses mask ROMs. There are no pin-equivalent EPROMs for those. I went down a rabbit hole with one of my 5342A, assuming that a ROM was faulty. In the end it wasn't.
Worth checking is the dipswitch on the microprocessor board. It is used to enable signature analysis mode. I found stories from people who had a bad switch, obviously that prevents the firmware from running correctly. I replaced the switch in mine, just because.
Wilko
|
Nice approach Wilko :) I will apply deoxit on dip switch to ensure function.
If it's a clue, it's been a while since I reached this same point in the service manual (by the way, I haven't had time to pull that thread yet, I'll tell you the results) because although input 1 (0.5 to 18 GHz) worked fine, it never passed the [SHIFT] + [1] test. The 75000000 never appeared on the display, but since the device counted, I continued using it. If that check tests the internal oscillators and there was never a correct signal, how has it worked for years?
It is a mistery...
|
Following steps on service decission tree: it seems to have proper signal forms and values. As you see in the photos of my scope, signals described in the service captures attached are present, but no continously. Then the A9 board is working properly, because when reset the unit, that sawtooth-like waveform is continous for a split second. Thus, entering center frequency manually and playing with [RESET] button, the counter start counting.
A big relief that the sampler is ok. That's for sure.
I think the problem is in the A10 (phase detector/divide-by-N assembly) because the delta phase signals 1 and 2 are not continous.
If you have a 5342A and can measure TP1 at A9 for me to confirm that sawtooth must be continous while the unit is sweeping the synthesizers, would be very helpful ;)
Regards
|
Acording to service manual, divide-by-N circuitry are ok. Found faulty component: U2 in A10, a phase detector (Motorola MC4044P). It has two inputs, divide by N signal which is present and changing period acording to CF in manual mode; and a reference input, fixed 50 kHz pulse, ok too. It's outputs are intermitent, so I think it is the faulty component which prevents A9 to sweep the synthesizers properly
I'll order new IC and try it out
Regards,
搁耻产é苍
|
Hello there!
?
As always happens in electronics repair, the first thing you see, no matter how clear and accurate it may seem, never solves the problem.
That IC hasn't made any improvements to the counter's behavior, so I was wrong. I have to continue investigating. I was pretty sure that the two signals, reference and pulses, coming to this IC are fine. But clearly there is some problem.
Some updates later...
Regards,
Ruben
|
Hello there!
?
I just bought and cleaned a 5344A and this forces me to return to repairing my meter. I was testing the 5344S system yesterday and noticed that the counter works fine, but only for random periods of a few minutes. The self check that shows 75000000 on the display (which I have never seen on my unit) yesterday worked. Obviously when the counter works, the 5344 works together with it without any problem.
?
We are therefore facing an intermittent failure, the worst of all. Please, if you have any suggestions on where to watch, ask and talk without problem. Something connects and disconnects randomly and renders the device useless or functional. But what is it?
?
For now I'm going to open the 5342 to take similar signals to the ones I measured last time and see the exact difference between when it works well and when it doesn't. My question yesterday above all was whether it was more difficult in auto mode than in manual mode, which only scans 50 MHz, but the failure was apparently independent of the mode used.
?
More news to come...
?
Best regards!
R.
|
RubenRubio
