Re: Alignment of HP 412A after rebuild, having trouble with the first step.
I have not worked on a 412 for many years. Is it possible the hum balance is NOT power supply hum but the residue of the chopper?
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On 11/30/2024 1:00 PM, Dan via groups.io wrote: Hello all, I am finishing up on a restoration of a HP 412A VTVM. ?It¡¯s quite accurate from the get go after the restoration.
I replaced every capacitor minus ceramics, I replaced pretty much every carbon composite resistor with 1% metal film of good quality, installed nos tubes that tested quite strong. ?I¡¯m not sure if I¡¯m doing the hum balance correctly.
It says to connect a scope to the amplifier terminals which happen to be on the back of the meter and adjust for minimal 10 hz signal. ? I¡¯m not seeing any 10 hz, only seeing stuff in the kHz.
If I adjust the hum balance pot it does change the waveform seen and it does lower the frequency, but I get nowhere near 10 hz and the frequency is jumping all over the place.
I did also notice that the hum balance adjustment also affects the zero point of the meter fairly greatly. ?After playing around with it I had to zero the meter using the small screw directly below the meter face.
How do I do this correctly? When adjusting hum balance in a tube amplifier I would adjust for lowest noise/hum. Would adjusting for the lowest point where the needle sits on the meter work? Equating that the needle is higher due to noise, this is a total guess here. ? I¡¯m sure there are others that have aligned this meter so I¡¯m hoping for some help.
Thank you,
Dan
--
Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998
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Re: Trying to go through alignment procedure for HP412A that I rebuilt, having trouble with first step lol
I apologize, I have a duplicate thread. I didn¡¯t realized the post had to be authorized before being posted. It can be deleted, use this thread for help.?
Thank you,
Dan
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Alignment of HP 412A after rebuild, having trouble with the first step.
Hello all, I am finishing up on a restoration of a HP 412A VTVM. ?It¡¯s quite accurate from the get go after the restoration. ?
I replaced every capacitor minus ceramics, I replaced pretty much every carbon composite resistor with 1% metal film of good quality, installed nos tubes that tested quite strong. ?I¡¯m not sure if I¡¯m doing the hum balance correctly. ?
It says to connect a scope to the amplifier terminals which happen to be on the back of the meter and adjust for minimal 10 hz signal. ? I¡¯m not seeing any 10 hz, only seeing stuff in the kHz.
?
I did also notice that the hum balance adjustment also affects the zero point of the meter fairly greatly. ?After playing around with it I had to zero the meter using the small screw directly below the meter face.
How do I do this correctly? When adjusting hum balance in a tube amplifier I would adjust for lowest noise/hum. Would adjusting for the lowest point where the needle sits on the meter work? Equating that the needle is higher due to noise, this is a total guess here. ? I¡¯m sure there are others that have aligned this meter so I¡¯m hoping for some help.
Thank you,
Dan
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Trying to go through alignment procedure for HP412A that I rebuilt, having trouble with first step lol
?
I replaced every capacitor minus ceramics, I replaced pretty much every carbon composite resistor with 1% metal film of good quality, installed nos tubes that tested quite strong. ?I¡¯m not sure if I¡¯m doing the hum balance correctly. ?
It says to connect a scope to the amplifier terminals which happen to be on the back of the meter and adjust for minimal 10 hz signal. ? I¡¯m not seeing any 10 hz, only seeing stuff in the kHz.
?
?
If I adjust the hum balance pot it does change the waveform seen and it does lower the frequency, but I get nowhere near 10 hz and the frequency is jumping all over the place. ?
I did also notice that the hum balance adjustment also affects the zero point of the meter fairly greatly. ?After playing around with it I had to zero the meter using the small screw directly below the meter face.
How do I do this correctly? When adjusting hum balance in a tube amplifier I would adjust for lowest noise/hum. Would adjusting for the lowest point where the needle sits on the meter work? Equating that the needle is higher due to noise, this is a total guess here. ? I¡¯m sure there are others that have aligned this meter so I¡¯m hoping for some help.
Thank you,
Dan
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Re: Troubleshooting a 8591e with opt 130
Yves,
?
Just a small additional update. I'm pretty convinced now the owner before the guy I got it from was already trying to fix this same issue. (I bought it from a guy who had bought it as broken but never had time to look into it).
?
I got a bit creative and started the adjustment procedure for the log amp. Most trimmers are at their end position so it's easy to restore.?
I used the analyzers own 0Mhz peak and it's step attenuator to get a Aux video out level near 1000mv. Officially the procedure tells to use an external synthesizer and the IF extender card, which I both lack currently.?
Ended up at 0hz span, ref level 0dB, att 20dB giving signal right at the top of the display and 1.0008V. Manual then gets unclear for me, says ampt increase 10dB on synthesizer, then set synthesizer to level from previous step.?
Anyway, continued in Lin mode, my aux video level dropped to 0.17v roughly and signal level also dropped ~15dB. So even if the input level had to be increased 10dB it would be too low. I found the slope trimmer at its end stop to already give max signal. Adjusting the trimmer could only lower the signal level. Feels like someone has been trying exactly that before me.. so probably we're looking at the combination of a failed component and a ruined adjustment..
?
Marco
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Re: HP 8341B 1992 firmware version
There is no limitation for 8510C version as I know.
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Re: HP 8341B 1992 firmware version
OK, so we both have the same firmware. I have both 8340B and 8341B with the same firmware. Do you maybe know what is the highest 8510C firmware version compatible with that 1AUG1986 for 8340/1B ?
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Re: HP 8341B 1992 firmware version
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Re: HP 8341B 1992 firmware version
Dmitrij,
Mine is also 2650 serial number. Which firmware version you have?
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Re: HP 8341B 1992 firmware version
Not sure.
As I see from assembly level service manual, there was many changes in hardware, including motherboard, CPU, YO, sweep control e.t.c.
Need more time to analyse.
My 8341B has 2650 serial number prefix and only two EPROMs too.
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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
?
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Re: Shielded probe cables?
Hi,
This might be what you are looking for:
I don't know pricing and/or if they sell in small quantities.
Regards,
/John
I don't know a manufacturer source, but one way to get nice tiny coax is to cannibalize an HP/Agilent logic analyzer chassis-to-pod "ribbon" cable.? The individual coax runs in the ribbon separate easily from each other, so any grouping down to one coax is possible.? A 40-pin cable will yield 36 x 50" of lossy coax, and the 90-pin version will yield 44 x 45" of (approx) 93 ohm impedance regular coax.
?
Another approach would be to just use the HP/Agilent probing system and make an adapter to connect to your KingstWiz.? You'd probably want to use the 40-pin probing system since the 90-pin system can be much more expensive.? With a 10kohm termination in the adapter, the 40-pin system would present the signal divided by 10, if the KingstWiz can handle that.
?
-mark
?
On Sat, Nov 30, 2024 at 03:53 AM, Anders wrote:
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?
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Re: Shielded probe cables?
I don't know a manufacturer source, but one way to get nice tiny coax is to cannibalize an HP/Agilent logic analyzer chassis-to-pod "ribbon" cable. ?The individual coax runs in the ribbon separate easily from each other, so any grouping down to one coax is possible. ?A 40-pin cable will yield 36 x 50" of lossy coax, and the 90-pin version will yield 44 x 45" of (approx) 93 ohm impedance regular coax.
?
Another approach would be to just use the HP/Agilent probing system and make an adapter to connect to your KingstWiz. ?You'd probably want to use the 40-pin probing system since the 90-pin system can be much more expensive. ?With a 10kohm termination in the adapter, the 40-pin system would present the signal divided by 10, if the KingstWiz can handle that.
?
-mark
?
On Sat, Nov 30, 2024 at 03:53 AM, Anders wrote:
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?
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Re: Troubleshooting a 8591e with opt 130
? 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
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Re: HP 8341B 1992 firmware version
Hi?Saevar, Dmitrij,
It turned out that my 8341B sweeper has 1986 firmware and it has only two eproms soldered. Will it be OK to solder four eproms with 1992 firmware?
Best regards, Wojciech
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Re: Shielded probe cables?
On Sat, Nov 30, 2024 at 12:53 AM, Anders wrote:
KingstWiz 32 ch analyser.
It's probably a Kingst LA5032 32 channel logic analyzer.
Though, their could also be a "KingstWiz 32 ch analyser"
Who knows?
I believe, I have a CheeseWiz 32 cheese analyser" ... somewhere
but, like the OP... perhaps... I don't know what I got.
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Re: VNA Resonance Methodology
OK thanks. As you can see, you can measure both resonance and Q at the same time with the shunt resonator method. The null frequency gives the resonant frequency and the depth of the notch can be used to predict the Q. However, the port match of the VNA has to be very close to a true 50 ohms resistive for the notch depth measurement. The source match (port 1) has to be especially close to 50 ohms of errors creep in. The old HP 87xx series of VNAs don't have a very good (uncorrected) source match at low frequencies so it's best to fit something like a known good 15dB attenuator at the end of the port 1 cable and a 10dB attenuator at the end of the port 2 cable if you every try and measure Q based on the depth of the notch. Then do a thru cal to normalise to 0dB and then measure the notch depth.
?
If you just want to look for resonance then you don't need to calibrate anything, just do an uncorrected s21 measurement and look for the null frequency at resonance.
?
If you want to try making a physically bigger solenoid using thicker wire (to achieve a higher Q) I can help predict the Q using the software program if that helps?
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Re: Troubleshooting a 8591e with opt 130
Yves,
?
I double checked and filled the table like you did
| ? |
Log |
Lin |
| VLOG2 |
-7.990 |
10,092 |
| VLOG3 |
-8,015 |
10,089 |
| VLOG1 |
-8,07 |
10,087 |
| -8VT |
-8,236 |
-8,236 |
| VLIN |
3,672 |
-6,624 |
| VLOG/VLIN |
3,695 |
-8,005 |
Some differences but not directly issues i'd say.
?
I checked but don't have a replacement LM339 on hand. I doubt that's the issue though, since at the output of the LM339 the full swing is measured, it's only after the resistor division in the "Gain Control Lines" part that the voltages are not reaching the expected levels anymore. So it seems the circuit after the Gain control lines division is loading it incorrectly.
?
I also checked the REF Level Cal signal. It's the output of a DAC on the Analog interface board, U106 pin 16.?
Measured in factory default cal and after self cal. level changes so it seems to function, don't know if its correctly though.?
| ? |
Fact Def cal |
Self cal done |
| REF Level Cal |
8,85V |
6,864V |
| Mrkr freq |
300MHz |
300MHz |
| Mrkr level |
-14,1dBm |
-5,1dBm |
?
Since my analyzer measures the cal signal in LIN mode at around -30dB~-35dB when in factory default cal it wouldn't surprise me if the additional gain is added because the signal is measured too low in LIN mode during selfcal.?
| ? |
Fact Def cal |
Self cal done |
| MKR Freq |
292,7MHz |
300,05MHz |
| MKR Level Log |
-14,3dBm |
-5,1dBm |
| MKR Level Lin |
-27,8dBm |
-20,2dBm |
?
I'm starting to think the full Log amp adjustment might have to be done because the lin and log gaines are perhaps not what they should be.. Although maybe the G4/G5/G6 voltage levels should be fixed first??
?
Marco?
?
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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?
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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:
On Wed, Nov 27, 2024 at 11:34 PM, DavidK wrote:
Adrian's Digital Basement
But...AFAIR... he's a software 'engineer' whose hobby (fixing old 8 bit computers), turned into a full time YouTube channel.
Well... okay.
But.
There are much better people on this forum.
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Dan
Anders
Michael A. Terrell