Motorola K1516AA K1516AE TCXO pinout

I found a canned oscillator hanging around my desk. It is a TCXO or even VC-TCXO marked Motorola K1516AE  1813-0535 10000000 Hz. No pinout. I haven't found a datasheet online, or I used the wrong search keywords.

On the other hand with some keywords I get directed to an eBay item of a replacement board for an HP spectrum analyzer, the HP 8562A. Usually old manuals show the schematic diagram and luckily the whole PDF is available on Keysight website. It is 462 pages long with only block diagrams. But I was VERY lucky since at page 6-25 (217 in the PDF), figure 6-7, in a "manual change" section the oscillator diagram is shown in clear! And the K1516AA TCXO pinout is there!

 

Page 6-25, power supply, TCXO and TTL level generator.

Zooming in for improved readability (click on the picture for a larger version):

Zoom on the TCXO part.

I have a K1516AE but I think the pinout shown for K1516AA will not be too far away.

 

 

MEMS microphone with TDA1308 amplifier board - 2

This is part 2 of my work on this module. Read part 1 here.

In order to get a usable configuration of the MEMS module described in the previous post, I wired it and started playing with resistors while listening to myself on a pair of headphones since there is enough signal to drive them.

The circuit as-is is so sensitive that it is like wearing a hearing aid!

First of all, it works from 2.5V and up. I noticed no difference in the output quality or volume at higher voltage: the final setup will need to keep the voltage within specifications, i.e. below 4V.

To reduce the overall gain R5 needs to become smaller. That's easy since we can parallel another resistor.

To reduce the microphone sensitivity I need an higher R6, so the original 0 ohm must be removed.

I chose to use 10k trimpot to speed up the process of finding a suitable configuration and started with R6. Rather than desoldering I cut it away. While increasing R6 has some effect on the sensitivity, the circuit starts humming when begins a noticeable reduction in the sound picked up.

I chose to keep R6 at zero ohm for now and moved on to R5. In this case the trimpot is in parallel to the existing 222 (22k) resistor since we need a lower resistance to decrease the gain. When the gain is adjusted it's like acting on a volume control, so both voice and hiss decrease of the same amount.

Fine, time to act again on the microphone gain R6. This time I kept leads short and fit first 330 ohm then 5600 ohm. In both cases I could notice the decrease in sensitivity but the noise/hiss was unchanged.

I will not spend more time debugging this module. It does work, it is very sensitive, but it is noisy. The noise might come from the op-amp or the MEMS module itself. Regardless, this circuit cannot be satisfactorily used with a transmitter. Maybe a different batch could yield different results, who knows.

Other uses? Probably recording sound that is then post-processed to remove the hiss is possible. I leave the comments open (moderated) so that readers can share their stories with this module.

My Ham Messe Friedrichshafen 2023

I'm back from Friedrichshafen Ham Messe 2023 and it is time to sum it up.

Hall A4 at 1/3 capacity at 9:18 day 1

Space usage was pretty much the same of last year, as I had documented for my future self on this blog. The crowd was more or less the same. We stayed from 09:15 to 15:30 on day 1, Friday.

Regardless of the shrinking (or not) of sellers and audience, Ham Messe is still unique as it gathers HAMs from all over Europe and the world.

What I bought:

• an energy measuring device for home (5 €)
• 8 sticks of machined pin sockets and 2 sticks of multiturn Bourns trimpots (2 €/stick)
• two Z303C dekatrons (10 €)
• a variable lab power supply with 8V, 18V, 80V independent outputs (25 €)
• T-shaped BNC adapters to play with the HP counter (1 €/each)

What I haven't bought:

• an HP signal generator "for parts" (probably working) we couldn't reach an agreement on the price
• other gear that I saw leaving the hall at lunch time, I think withdrawn from owners not actually sold!
• Nixie tubes at current market price
• what looked like homemade HF RTX from HA and YU sellers, since I have no HF antenna at home
• other aero DME receivers that I bought last years, too bad
  

That's it. Next year the Ham Messe will be held on 28-30 June, 2024, if it will take place.

Three more pictures.

Pretty early days vacuum tubes...

 

... quite recent lab instruments.

I didn't know of this initiative from the nearby city Tettnang.

An HP 5326B enters my lab

It was just a matter of waiting until I could buy an old/surplus/vintage HP device with Nixies for little money. Unknown conditions, of course.

I bought an HP 5326B Electronic Counter in Basaluzzo HAM flea market (June 2023) which was designed to measure 100 mV up to 50 MHz and display the result on 7x B5750 Nixies (or similar). It also has a 1000Vdc voltmeter measured using an internal V/F converter.

Display board of HP 5326B.

On a first visual inspection the unit was serviced once to replace a 1820-0119 IC that was actually rebuilt with TTL ICs! It had loose screws of the top cover, so I wasn't hoping for the best but I powered it up nevertheless.

Well, well, it sprang to life and seemed to give proper readings, so I needed to read the manual to check for proper operation and calibration check.

The unit is in proper working order. The stock 10 MHz reference oscillator is spot-on at least for the precision I can reach in my lab. The DVM might be reading 1% high my calibrated voltage source, but I'm comparing it to other uncalibrated, various era, less resolution devices.

I like the possibility to make it count events until the reset button is pressed, which means it can become a clock with very simple interfacing.

The rebuilt 1820-0119 does not implement leading-zero blanking so the 7th digit is always on. I'm even thinking of building a modern replacement of the counter+buffer pair 1820-0119/1820-0116 by means of a microprocessor. This way I regain the leading-zero blanking and I might even add the 8th digit option!

I played a little game: how far does it measure beyond the 50 MHz upper limit? I used the NanoVNA as a frequency generator using the "CW mode" (alternatively you set the Span to 0). I have no idea of the signal amplitude at this point but it reached 95.000 MHz! The counter is 9.3 kHz high (0.01% or 100 ppm).

HP 5326B measuring 95 MHz.

 

 

MEMS microphone with TDA1308 amplifier board - 1

A local HAM has asked me help to integrate a microphone module in his mobile setup. He was directed to the little MEMS/silicone microphone module shown in the picture below with very positive comments.

MEMS microphone with amplifier circuit.

The problem with his initial setup was a wiring error in the RJ plug, but with that fixed the module showed an unexpected effect: even in complete silence the circuit would produce a strong hiss like driving at 100 km/h with open windows, and the modulation was extremely loud.

Digging a bit further on aliexpress I found a description of the circuit:

• Working voltage: DC3V-5V
• Output about 30mw, can directly drive ordinary 32 ohm headphones
• R5: amplification adjustment resistor, resistance value can be used 4.7k-100k [cut] The higher the resistance value, the higher the gain [the board comes with 22k]
  
• R6: for the microphone sensitivity adjustment resistor, shipping default for high sensitivity (resistance value of 0 ohms), the resistance can be selected from 0 ohms -10K between [cut], the greater the resistance value of the resistor, the lower the sensitivity

Very good information: the stock board has maximum microphone gain and middle amplification gain. 

I also checked some random datasheets from Knowles SiSonic product range and noticed that 5V is usually the Absolute Maximum Rating for their MEMS microphones.

He gave me one module to experiment with. Stay tuned!
 

 

 

No output from Arduino TVOUT examples

I am in the process of reverse engineering an industrial monochrome 12" monitor, mainly trying to figure out the pinout to drive it.

My initial analysis of the circuit, based on TDA1175 and TDA1180, concluded that it needed a composite video. So I programmed the PAL sample of the TVOut Arduino library on a Nano (clone) and got nothing. I got no signal on the TV, and nothing was moving under the oscilloscope scrutiny.

The library is scarcely documented, but reading here and there I understood that the resulting circuit was originally meant to produce overlay text on an existing video stream. This means that the Arduino sketch needs a sync input to stay ... in sync. Without an input sync, there's no composite output (this was confirmed later).

I checked the code and in the setup() portion there is this initialisation call:

TV.begin(PAL|OVERLAY);

Well, changing it to remove the OVERLAY requirement like this:

TV.begin(PAL);

Recompile, reflash ... and the composite video comes out.

Green phosphors here I come!

IC decapping with paint remover heat gun

I'm not sure where I read about an easy way to decap integrated circuits with heat, but it's certainly not three years ago (when the author published his demonstration video):

Well, while looking for something else in a storage area I found a good candidate to try the same experiment, but in WDIP package: a part marked R3268B with no daatsheet on the Net.

It takes more time to setup the heat gun (paint remover) that doing the job itself. The plastic case gets brittle with heat and it breaks in small pieces. Be careful they don't fall inside the heat gun.

This is the result of my first exposed IC:

I think I was unlucky as something covers the active area. The other side is uniform, like a large ground plane. I could see that pins were quite thick, so perhaps the IC was a motor driver or something that carried large currents. I'll try again with other chips.

 

 

 

Behringer BX1200 Ultrabass

A friend's son plays bass. He was given a Behringer BX1200 Ultrabass combo amplifier with some problems, and he asked me for help.

The amplified bass was distorted, but using a back panel input the output was ok. Then the fuse blew up and that was the end of their troubleshooting. So they brought it over together with a schematic diagram found online (revision H in our case), which is very helpful.

At the first glance I noticed something weird at the front input sockets, that I had to rebuild following the schematic. Actually I wired it for a passive instrument because someone had removed the switching sockets in favour of simple 3-terminal ones, and the boy has a passive bass. It's a compromise I will document.

I went all the way to remove the large heatsink to check capacitors and PSU voltages, that were within specs. Hint: don't touch this area if voltages are correct. You can pick voltages across the diodes. I added the screws that secure 7815 and 7915 to the heat-sink since who came before me had forgotten them.

This gave me a working BX1200 that still needed a new master volume potentiometer. The diagram just mentions 50kB. The specific part is marked ALPS. Digging through the Alpine technical documentation I came up with these specifications:

Alpine ALPS 50k 30mm (total height) 3 pin, vertical, with collar, flat shaft, without detent, shaft length 25 mm. The closest part I could get is RK09D1130A1L, giving up the logarithmic response. We bought an Alpine part but there are alternatives too. In 2022 money one of these Alpine potentiometers costs 2€/US$.

If you have to replace the master volume pot chop off its pins and then desolder and remove what is left on the board: you will not be reusing that pot anyway! Remove all solder leftovers or the new one will not enter the holes.

That was an easy fix, at last!