Wow I learned so much thanks for taking the time!! I acquired an HP 8924C and this video helped , I am learning how to align ham radio gear and such, again thanks!!!

@EriksElectronicsWorkbench

7 ай бұрын

Glad to know you found the video helpful! The HP 8924C does have a spectrum analyzer function among other features.

Normally a pot used for an audio control has a log taper, also called an audio taper, not linear. Was the original one linear or taper? My hp8593A has a volume control but I believe it has no demodulator or speaker. An older SA I used to have had a chart output, since it was a voltage, when connected to a speaker, I could hear local stations like you did. My SA became intermittent. The switching PS had failed. What clued me off was checking power supply waveforms with a scope, noticed a lot of ripple. I found a bad electrolytic cap that had gone bad, I believe the esr had risen to an unacceptable level. Because the PS was not made by HP, a schematic of that portion was not available. You gave a nice overview on the controls of the SA, thank you.

@EriksElectronicsWorkbench

4 ай бұрын

As I recall the volume pot was log or audio taper type when I checked its resistance. Your 8593A needs option 102 for demodulation. It may have had that circuit card at some point and then it was removed but the speaker was left. Yes the switch mode supplies often fail from faulty capacitors. I've recapped quite a few switchmode supplies in scopes, spectrum analyzers, etc. Thanks for watching the video!

@Aligreta

21 күн бұрын

Log taper indeed causes higher ohm excussions at the beggining on its linear region then less and less, thats logarithmic. That being said the behavior for low settings will match. Here problem is too high audio gain to start with

Good to show us the Sencore tester. I wonder what would burn a dried and cracked Rifa, is it high ESR?

@EriksElectronicsWorkbench

23 күн бұрын

The capacitors are basically turning into resistors as the dielectric breaks down so they start passing excessive current which heats them up.

The PowerSupply of mine just blew up. One of these RIFA capacitors vanished into a hughe cloud of smoke. The PSU is one of those not designed to be repaired. Two boards mounted overhead and cables soldered into the printed circuit boards. I disassembled the psu in total and installed connectors to be able to maintain the psu more simple in the future. Luckily the installation of a replacement capacitor solved the issue. Nevertheless the unit is still smelling in operation. My failure was not to follow the standard procedure to review and rebuild a psu in general befor powerup of an used unit.

@EriksElectronicsWorkbench

2 ай бұрын

Those old RIFAs are pretty good at letting out the smoke! I make it a habit of inspecting and looking for them, they were used everywhere.

I have a much modest model of the same analyzer. I think iy's great. I wanted for this one (basically for the bandwidth and the rest of the things mine doesn't have -volume, etc.). In fact, you solve the problem; the volume is now much more "usable", but...I can hear some kind of "click" when you turn up the volume knob, like a switching noise -it doesn't sound to me from absolute zero volume, and going up. So I honestly think that the problem is not solved (forgive me). Of course, it is much more pleasant to the ear, but it stil switches on the sound. Lower, but still start sounding not from zero. Well, maybe is more than enough, of course (in fact, it is). And one more thing: do you know were to obtain one like this?. I use a lot of audio analysis, and mine has a BW of minimum 9kHz (it's the HP 8590B). And, of course, thanks for sharing your excellent videos.

@EriksElectronicsWorkbench

8 ай бұрын

I think the click you hear in the audio is the spectrum analyzer beginning to demodulate when I already had the volume turned up a little bit. The audio is free of clicks and noises when the volume control is rotated. If the audio is already being demodulated the volume is very smooth from zero upwards. These models can be found on eBay (various conditions of course) and for a working and calibrated unit you can try Global Test Equipment or AllTest Instruments Inc. For audio testing you would not want to connect a high powered audio amplifier to this unit. You should consider adding an active probe which will give you a high impedance input.

@fichambawelby2632

8 ай бұрын

@@EriksElectronicsWorkbenchthanks a lot for your answer. It’s a pity that here in Madrid is nearly impossible to buy one of these. Ebay Spain have as much as one or two, extremely expensive units. Lucky you!

👍

Im gonna buy one of these. What should i look out for before buying? Only thing i know about it is that the range between 3-6,5 ghz is not working and is bypassed

@EriksElectronicsWorkbench

6 ай бұрын

It comes down to what you feel your abilities are for doing a repair and possibly calibration. This is a very complex instrument internally. Here is my approach when considering an instrument, first download the service manual and understand what you will be dealing with. Look over the unit and see if it has physical damage that would be unrepairable including any serious burning on the CRT. Consider the unit cost and allow cost for any repairs or parts.

The FM signal you receive over the air has a decent amount of power. What about FM signals that are so low in strength, they'd require a large amount of gain? Maybe this unit was configured for a special use case. Just wondering if putting an attenuator(s) between the antenna and BNC plug could change the way the volume control knob behaves.

@EriksElectronicsWorkbench

4 ай бұрын

When I test with the FM signal the strength going to the analyzer from my simple antenna is in the low microvolts. The analyzer can detect lower and also much higher amplitudes. An input attenuator would not affect the audio. The signal amplitude is not what controls the audio volume unless the signal is so weak it can no longer be demodulated. With FM (frequency modulation) it is the deviation of the carrier frequency that carries the audio. I tested the analyzer on FM (and AM) signals of different levels of modulation and the volume control acted the same on any of them. With the changed resistor it now has better volume control range.

@c4t4l4n4

4 ай бұрын

Thanks for you detailed reply. I learned something! @@EriksElectronicsWorkbench

have you checked the high band (2.9-6.5) reading correctly? that's the biggest issue these 856xE series have other than the YTO being bad which is not the case here obviously.

@EriksElectronicsWorkbench

7 ай бұрын

Yes the instrument is functioning correctly on the high band.

Are you sure the capacitor in series with the replaced resistor is OK?

@EriksElectronicsWorkbench

8 ай бұрын

Yes, with the resistor removed the capacitor is isolated and can easily be checked. I tested it for leakage, ESR, and value and it passed.

@andersjohansson8588

8 ай бұрын

@@EriksElectronicsWorkbench Strange that you had to change to a significantly higher resistance.

@EriksElectronicsWorkbench

8 ай бұрын

The resistor sets the amplifier's gain. If you don't have the external resistor (infinite resistance) the gain will be 20 (26 dB). As the resistance is decreased the gain goes up, the extreme being no resistor and only a capacitor which will give a gain of 200 (46 dB). So it makes sense the original resistor at about 82 ohms was giving a very high gain and the new resistor at 4.7K ohms reduces the gain substantially, now at about 26 (28.3 dB). @@andersjohansson8588

@andersjohansson8588

8 ай бұрын

@@EriksElectronicsWorkbenchHmmm… are you saying that from ”your” perspective, HP made a bad design decision, choosing the ”too” low resistance?

@EriksElectronicsWorkbench

8 ай бұрын

yes based on how the circuit works and the results you could say that.@@andersjohansson8588

Hello, if anyone can help, I need the firmware for the HP 8594A, thank you.

16:13 That's because the only way to play Journey is on LOUD. IDK man, seems like a bodge to me. The audio still just suddenly goes "on", just at a lower volume. Anybody here with the same model who can test how theirs works?

@EriksElectronicsWorkbench

4 ай бұрын

All of the measurements around the audio circuit are correct. The resistor I changed sets the amplifier's gain. The gain was set very high at the factory by the resistor HP used. My resistor lowers the gain and the amount of gain figured mathematically from the data sheet specs matches the measured values. The sudden sound on you noticed is just the analyzer sweeping and then restarting the demodulation. The demod time is adjustable.

That resistor must have been an error ?...cheers.

@EriksElectronicsWorkbench

5 ай бұрын

Seems like it was not the best value for the application. No other components in the circuit are defective so the change I made was not covering for another problem.

So HP put the wrong resistor in?

@EriksElectronicsWorkbench

7 ай бұрын

Looks that way. The audio power amp IC is just doing what it is supposed to by setting the gain depending on the resistor value. That info is on the part data sheet. I don't know why HP would set the gain so excessively high.

Those RIFA capacitors are bad news. Especially if the instrument is to run on 240 volts as used in Australia. Two instruments I bought from 110 volt countries went up in smoke within a Minute of applying mains. These capacitors are exposed to the mains potential even if the instrument is turned off.

@EriksElectronicsWorkbench

7 ай бұрын

Yes I've heard about devices being switched over to 240 volts and the old RIFA caps explode in no time. Correct that the caps are usually unswitched on the AC line.