|
Re: Troubleshooting a 8591e with opt 130
Yves,
?
I agree, might be defective parts but i'm pretty sure alignment is also an issue.
Measured the 3 trimmers for G4, G5, G6 in circuit:
Measured in circuit
R27 0.4840k R30 1.0731k R33 0.7642k?? They are all pretty close to the end of the range, I tested the range of R33 and was indeed 10k, returned it to the previously measured value.
?
But other trimmers on A14 are also worrying me, R69(-30dB), R10(offset) and R23(slope) are all at the end stop of their range. Can't imagine that being the result of a proper alignment procedure, unless caused by a component failure somewhere.?
R69 is a 1Meg trimmer controlling the PIN diode at the input of the 4th stage, see below. It is currently all the way to -8vT, which probaly means Pindiode CR16 is sinking a lot of signal away..?
?
R10 and R23 are both part of the Temperature compensation powersupply. The differences of -8VT (yours -7.72 and mine -8.5) and TP1 ( yours was -0.43/+14.24, mine was -5,5/14.25) are probably caused by this (mis)alignment.. I'm guessing this might also be the cause of the G4/G5/G6 negative voltage issue.
?
I've ordered some IF injector PCBs as found in the group files, ( [email protected] | Files )? and an LNA to add to my TinySA to have the required output level range for the log amp adjustment procedure. But I feel like trying to adjust them a bit already, it's not hard to restore them to the previous setting since it's just all the way to the end anyway..?
?
Marco
?
|
|
Re: Troubleshooting a 8591e with opt 130
¿ªÔÆÌåÓý? Marco, ? For your control LOG/LIN switch, all seem good. For third converter RF CAL GAIN, I have 7.454V for -20dBm, but with CORR=OFF, same DC voltage, but -13.6dBm. For -20dBm on screen, I have -43.5dBm at AUX IF OUT at 21.4MHz, this is the input signal to LOG/LIN amplifier & detector. And for CORR=OFF, I have -37.6dBm. ? Since the result between LOG and LIN are different, it is certain that there is a problem, alignment or defective parts. ? ? Yes, the most logical thing would be to start with the G4-G5 and G6 controls. Are the potentiometers, OK? I would measure their ohmic value in the circuit to have a reference. Maybe these potentiometers are defective, or someone has touched these alignments. ? Yves |
|
Shielded probe cables?
If we think about the nice logic cables that come with the HP MSOs, ie a flat, presumable shielded cable, a box and then thin, flexible, presumable shielded cables that go to the probes. I would love to have something similar for my KingstWiz 32 ch analyser. Anyone know a good source for thin, flexible, shielded cables? |
|
Re: Tantalum Capacitors
I've watched a few of his videos, and his troubleshooting methods are irritatingly slow. He reminds me of newly graduated tech school students that shotgun ded equipment rather than develop the skills to make repairs affordable. I repaired hundreds of 8-bit computers with a logic probe and a 500 KHz scope before I finally bought a Tek 453A. He seems more interested in showing his gadgets than doing logical troubleshooting. You learn the most common failures, and good methods to find the problem/ Bad AM was a high failure item, which a lot of foreign made ICs in questionable packaging.? A look at th data line on each would quickly reval the worst , and I would replace all sigh if four or more were bad Some brands were so flakey that you recognized them, on sight as needing replaced. I repaired most of it without schematics. On Fri, Nov 29, 2024 at 8:42?PM Roy Thistle via <roy.thistle=[email protected]> wrote:
|
|
Re: Troubleshooting a 8591e with opt 130
¿ªÔÆÌåÓýMarco, ? For my 8595E, module A12, after power on, if CORR=ON, IFA1-A4 are OFF and IFA5 is ON. From this point on, only when the REF LEVEL is at 0, +10, +20, +30, +40, +50 and +60dBm, IFA5 is ON, all other cases, IFA5 is OFF. ? If I put CORR=OFF, the level read from the 300 MHz calibrator is -13dBm. So, I put an external fixed attenuator of 6dB, for a level of -19dBm, and I did a CAL AMPTD. I looked if IFA5 becomes ON by testing the different possible REF LEVEL, but this did not change anything in the previous results. Either the attenuation values ??are predetermined, or, A12 is tested in relative mode from the external calibrator, that would be the reason why this did not change anything. ? On the other hand, the fact of having reduced the signal from the 300 MHz calibrator, changed the value of the gain at the third converter output: REF LEVEL CAL. It is a variable gain amplifier controlled by DC voltage. This calibration is done in the first minute of the CAL AMPTD calibration. Yves |
|
Re: Tantalum Capacitors
FWIW:
Here in Colorado Springs (dry climate, high altitude) I seem to have MUCH fewer cap failures than everyone else. I can't remember the last time I found a tantalum that was actually bad (and certainly not shorted). I have NEVER seen an exploded Rifa cap.
I *occasionally* find a dried-out electrolytic (especially in ordinary commercial radios and such), and some old paper coupling caps turn out to be a bit leaky in commercial gear (but almost never in higher-standard gear like HP test equipment).
?
I *assume* that the dry air and/or high altitude is the difference.
I have NEVER felt the need to pre-emptively replace caps, like so many folks seem to think is essential. One of my 1960's-vintage HP machines had two examples of dried-out electrolytics of a specific brand/type, so I did replace a couple more of the same type that were in it (even though they were still working).
?
Pete
? |
|
Re: Troubleshooting a 8591e with opt 130
¿ªÔÆÌåÓýMarco, ? This is my measures about LOG/LIN switch ? ? The LM339 U108 has open collector outputs, as the graph shows, although it is not to scale with the configuration in your 8591E, but you can see that if the sink current exceeds 10mA, the voltage will quickly rise again depending on the current. If you ever had a replacement LM339, it might be a good idea to change it to see how it behaves, or by isolating the outputs one by one, see if the voltage drops back to the nominal value. ? Yves, |
Anders
Michael A. Terrell
Jinxie
saipan59 (Pete)