Category Archives: Test Equipment Repairs

For some, it is like solving crossword puzzles: fixing defective test equipment. Preferably, mid-70 to early 90s vintage.

Micro-Tel MSR-904A Microwave Receiver

Micro-Tel MSR-904A Microwave Receiver: the monitor output

2014/09/28 Simon Leave a comment

The MSR-904A has a few outputs (and inputs), most of them, easy to identify, but two, are pretty much a mystery to me, with no schematic – their function is clear, but with all these wires TTL logic boards -difficult to guess the pinout.

The more easy thing first, the monitor output. Arguably, this was intended to be connected to storage displays, digitizer, chart recorders, or the like – to more permanently record the activity over the bands.

So, what do we have. Using a scope, and a multimeter, and activating more or less all the functions of the apparatus, that’s what I found out.

Sorry for the rough draft, but any questions, please ask – for the given purpose, good enough.

The only pin that doesn’t do much, is pin 9 – always stays on logic 5 V – maybe a +5 V supply line? Doesn’t seem to be an essential function, anyway.

Micro-Tel MSR-904A: RF tuner block diagram and component specs

2014/09/28 Simon Leave a comment

Just to learn a bit about the way Micro-Tel was doing their engineering, let’s have a quick look at the way in which it functions, at least for the RF front end. After some study and tracing, here is the block diagram:

Some parts don’t have model numbers – because these are hidden, and I don’t want to take the thing apart.

Luckily quite a few of the parts are still available, and datasheets are available for most. The YIGs are Avantek, have a customer part number, but I assume, essentially, slightly modified line item parts, with some specific specications. The only really uncommon part, is a “TREK MICROWAVE” 0.48-2.01 GHz 3-stage YTF. Didn’t know that such low frequency YIG filters existed, this has serial #00003.

Even more, TREK doesn’t ring a bell for me, and the filter really looks very much like Systron Donner technology, with the characteristic color, and square-cube shape.

As it turns out, TREK acquired the YIG division of Systron, some time around 1984… so, this mystery solved.

The only part where no data seems available is the 2-18 GHz mixer, Avantek SX83 series, but can’t find a -1612 model anywhere.

Some datasheets:
5B120-2330_25-O_OP – 5915011438953 _ chebyschev 2330 MHz 25 MHz bw

k&l 5L120-300-0 low pass 300 mhz

8L120-2050-0 low pass – 5915012428744 _K&L filter

narda 4244-6 082-Couplers

a34 datasheet

qbh 101 amplifier datasheet

narda 4203-10 coupler

Micro-Tel MSR-904A Microwave Receiver

Micro-Tel MSR-904A: some basic repairs

2014/09/27 Simon Leave a comment

Quick initial assessment, these are some of the items that will need attention:

(1) Exterior. Need to fabricate instrument feet, re-paint the panels, handles are missing – either need to get spares, or fabricate replacement handles (can only be done back at the main workshop in Germany, lacking machine tools here).

(2) The ground leakage -need to check the power supply. Hope it is not the transformer or other critical part.

(3) Power cable. Absolutely non-standard! Uses a BENDIX connector, 3 pin, type PT02E8-3P-027.

Interestingly enough, found a suitable cable, especially made for the MSR-904, on xbay, Army surplus! PN: SC-D-627094-5FT NSN:5995-00-165-3806, the guy has more then 10 pieces – seems the Army was really worried to run out of cables for their MSR-904s.

(4) The frequency display works but doesn’t show the right frequencies.

(5) The F2 adjustment (upper sweep stop frequency in F1-F2 mode) doesn’t work.

(6) Figuring out the major adjustment pots – this is all documentation I have:

(7) Figuring out the pinout of the “Monitor” port (intended to connect a storage scope, I might connect a digitizer), and of the “Remote” port – the remote control signals (TTL).

(8) Figuring out the external frequency control and phase lock voltage requirements.

(9) Drafting a block diagram of the RF deck and IF chain, just to better understand the inner workings, and to see, which parts-components Micro-Tel used.

Now, on item (2).

The power supply –

It’s held in place, and held together, by a cup full of screws. And, it has a layer of what is presumably Mu metal (high magnetically shielding sheet metal), to keep the 50-60 Hz in the transformer.

The filter, at the input, it is a sight in itself. Not sure how much it would cost to fabricate a custom aluminum case of this size, and to manually assembly it these days. Parts value alone, over 250 USD.

Well, and as it turns out, exactly these parts are leaky. SPI filters, 51-321-610, still available, after being around for 30+ years, at Mouser and elsewhere – 119.64 USD each, 18 pcs minimum order….

The spec data:

After a quick thought – I will give these parts a miss. With all the shielding, transformers and wires, we can do without hermetic feed-through filters – keeping in mind that also the bottom and top lid of the unit have ventillation holes.

So, filters removed, and wires re-connected… and, quite to my satisfaction, no ground leakage any more – not even a few microamps.

Before putting it back together – quick check of the power supply – all seems to be working fine now, and well adjusted.

Item (4) – complicated. Took me quite some hours. The frequency meter is acutally a voltage meter, and this is controlled by the tuning voltage, and a complex digital circuit spread over some hard to reach board. After searching around – it’s just a defective CMOS multiplexer switch, setting the gain of one of the voltage conditioning stages (which are needed to handle the various bands). It’s and CD4051, standard item, no problem. Put in a good one, from another part of the circuit that is not criticial at this point, and ordered a few spares, just USD 1.75 for 3 pcs, including shipment, from Macau.

On item (5) – the sweep circuit is pretty similar to the Micro-Tel SG-811, and for the SG-811, I have the schematics around.
It uses a dual 10 turn potentiometer. 10k.

Helipot 6108 series, a type common to high-grade analog-control instruments. Seems that one of the stages (the stage that controls the sweep range) is defective – the hybrid resistance material used for the pot (these don’t use wire, because they are made for high resolution applications) is open at the “cold” end – sweeper is always at full scale.

As these are all fully sealed units, no way to repair – found an exact replacement second-hand, for a reasonable charge. For the time being- changed the wires: the F2 display (controlled by the second stage of the pot, which is still working), has been disabled, and the wires changed so that the acutal sweep range is now controllable – so I can do all adjustments, just don’t get a display for the F2 frequency.

Well, and after all this, the unit is at least basically working, responding to controls, and not triggering any fuses. To move things further, setting it up with a few GHz range synthesizers, and an EIP 545A counter, for some first tests with RF.

To be continued…

Micro-Tel MSR-904A Microwave Receiver

Micro-Tel MSR-904A Microwave Receiver: the big box arrived!

2014/09/27 Simon 4 Comments

Look what I found on the doorstep yesterday:

Wrapped in 20+ feet of bubble wrap, nothing less than a Micro-Tel MSR-904A Microwave Receiver, needing some TLC, later, to be added to a special equipment collection elsewhere.

The MSR-904A. Arguably, it is the last member of a series of 18 GHz+ receivers, build by Micro-Tel at Baltimore, MA, and intended for surveillance work, by governmental agencies. If you ask the right people, these receivers are pretty famous, and have been considered a strategic item for a long time.

They are build using all discrete parts, and hardwired CMOS and TTL logic. After all, many parts, but if you have seen other Micro-Tel instruments, not too unfamiliar. Some say, 80s technology, but actually, is is build in time-less style – from the best components available (not only at the time – these components, YIGs and filters haven’t really improved since).

Some performance data:
Frequency range: 0.5-18 GHz – fundamental mixing; fully YIG pre-selected over the full range (using 18 dB drop-off filter, i.e., three YIG spheres; one preselector for 0.5-2 GHz, the other, 2 to 18 GHz).
1st Image rejection, 70 dB, and 65 dB at above 12 GHz.
IF rejection: >70 dB
IF filters: 100 kHz, 1 MHz, 5 MHz, 30 MHz – quite handy.
IM3: about 5 dBm
LOG and LIN detectors
AM and FM demodulator
Spurious: 90 dBm at input equivalent over full range.
Noise figure is about 20 dB

Note: All in all, 3+3+1+1 = 9 YIG spheres are used, and an uncounted number of filter crystalls. The 100 kHz 21.4 IF filter, it’s quite impressive.

In the 2 to 18 GHz range, a 250 MHz-21.4 MHz IF chain is used, with LO 250 MHz above the signal.
For 0.5 to 2 GHz the signal is mixed with an additional 2.08 GHz from an auxilliary LO. I.e., LO frequency is 2330 MHz (2080+250 MHz) above signal.

The other great things about it:

(1) Fully fundamental mixing, using YIGs – lowest phase noise possible. Fully preselected.

(2) Unit has a 250 MHz IF output, with about 40 MHz bandwidth – this makes this unit ideally suitable as down-converter, if you want or need to receive at medium to high GHz frequencies. Can be directly fed to any SDR for demodulation. The MSR-904A has very small group delay, seems pretty suitable for handling of digital modulation schemes.

(3) It is fully remotely controllable, and has a phase lock input – will hook it up to a ADF41020, and/or a fractional-N PLL, same PLLs as already developed and tested for the Micro-Tel 1295 receiver. Such PLL unit will go along with the MSR-904A, once the repair and proper adjustment and testing is finished. Micro-Tel used to offer a frequency stabilizer (PLL) for the MSR-904A, but I have never seen one offered. If you have one, please let me know!

Two downsides – NO serice manual, no manual or documentation at all. If you have one, even if only for another MSR unit (MSR-901, MSR-902, MSR 903), please, let me know.

Second downside – the condition. Well, there don’t seem to be many of the MSR-904A around for sale any more. One unit I know off, but it doesn’t have the panoramic (scope) display. Other might be available, at outrageous cost. This unit was sold even blow the market value of a fraction of the components.

Note the tuning know – different from the typical Micro-Tel style. But nevertheless, seems to be the original, unmodified part.

The full repair, it will be a major job, because currently, it is a bit beat up – I wish, the earlier owners would have treated it a bit more carefully, and Micro-Tel should have never touched the green paint that just isn’t lasting and a sticky mess on a good number of their instruments – fortunately, only the panels are affected, and these are easy to remove – re-painting already in process!
Also, it doesn’t seem to work well, powers up, but seems to have a leaky supply – keeps tiggering the RCD. It needs a through inspection.

Cosmetically at least, the inner working are in much better shape than the exterior would suggest.

Center – edge-connector boards, mainly YIG driver and analog control. The metal box on the right – the RF box with the microwave stuff. The other items – IF converters, detectors and so on. Everything: very well shielded.

2.08 auxilliary LO. Mixers.

A Narda 2-18 GHz broadband -10 dB coupler. Still available from Narda today!

The preselectors: S082-1630 (2-18 GHz, might work up to 20-22 GHz), and a custom Systron Donner 0.48-2.05 GHz YTF.

HP 3562A Dynamic Signal Analyzer

3562A Dynamic Signal Analyzer: LCD retrofit NewScope-5

2014/09/27 Simon Leave a comment

Yet, another job related to the 3562A, same machine that also had the ROM board defect. This unit also has a weak display, and I have been asked to check replacement-repair options.

After a brief search, there aren’t any spare CRTs around, for the 1345A display used in the 3562A. The last good ones might have been purchased-stockpiled some years ago, by corporation that need to keep equipment going.

Well, fair enough. Luckily, failed CRTs and their limitations are a common feature of dated test equipment. So other have already invested time and effort to provide a solution: the LCD retrofit.

Why not just replace the whole instrument, with something new, up-tp-date, and more manageable? Several reasons:

(1) Many clients have proprietary-custom software running certain automated tests, using certain types and specs of test equipment. The final product specs have often been agreed upon with the OEM, in contracts that are a big hazzle to change. Some of these products, in fact, most, have long service life, so the test rig needs to be kept alive, more or less, at any cost.

(2) Cost – well, new test gear of the proper kind is outrageously expensive. Not taking about plain stuff here, but powerful equipment, network analyzers, spectrum analyzers.

(3) Servicabilty: talking about smaller businesses, not big corporation, often it is quite handy to stick with somewhat dated analyzers etc, because they are perfectly up for the task, the operators are trained, both in using and serviceing them, and often, spare units-parts units are around and can be procured at a fraction of the cost of repair of new equipment.

(4) Quality. Arguably, and except for new digital signal-fast scope stuff, the instruments build in the late 80s and early 90s might be the best ever build. Most of them have specs and typical performance far above what most regular quality can provide nowadays. The reason is simple, in the 80s, these rigs were build for the military and related agencies as the key target market. Nowadays, for consumer electronics, consumer communications… One exemple: the HP 8566B spectrum analyzer. Not sure about the price of such equipment nowadays, if build new – certainly 6 digits. On xbay, they go for about few cents per USD list 1985 list price… and be assured, no big deal to get them working in-spec.

The LCD replacement kits have come down in price considerably – earlier on, still USD 1000+, now, check this out:

USD 400. Not bad. This includes display. LVDS driver. And certainly, the controller board, to adapt the display to the 3562A.

Here, from the inside:

The display: it’s a rather dated SHARP LCD DISPLAY, LQ057V3DG02, TFT 5.7″, 640×480. But rather then stockpiling CRTs, I now have a few of these in stock now – found them for about 15 EUR each surplus – this will allow service of the LCD-retrofit units, for years to come, without any need for modification to fit another type of LCD display…

I can tell you, such retrofit is worth every dollar. If you have any of the CRT analyzer with the screen gettin dimmer. Don’t hurt your eyes.

A quick glance at it – it’s great to work with it – color display, rather than dim green display.
The color settings work fine for the most part – there are some little bugs in the NewScope-5, related to the text color, in some menues (first character has different color). However, this has really no impact on the great advantage of such LCD retrofit.

HP 3562A Dynamic Signal Analyzer

3562A Dynamic Signal Analyzer: EROMS fixed, finally!

2014/09/27 Simon 1 Comment

The last and only remaining item to get the 3562A with the defective A3 ROM Board (03562-66503) back into service, replacing the defective EPROM. Well, I thought this would be a 30 minute job, but it ended up taking a few hours longer. Why? Multiple reasons:

(1) A bug in the AVR eprom reader software, specifically written to read the 3562A rom board (and similar boards, or other instruments – software always needs some adaption). One of the address lines was not toggled-ended up with corrupted data read from the “good” rom board.
Learning for today: always check the EPROM data read for validity, by checking for repeat patters, and by reviewing all the byte values. There should be at least a few 0xff values, otherwise, one of the data bus lines may be broken.

(2) Turns out, there are two versions even of the Rev B rom board, same part number, but eproms U118 and U218 that have the checksums are different. So, needed to desolder these two as well, and replace with the updated version from the working board.

The good ones on the left, the bad guys on the right…

(3) With all this, my eprom programmer, the only one I have that can handle 27256 EPROM had a defective jumper! No contact on one of the address lines….

After all these efforts: that’s the board, after repair:

The replaced EPROMs are now in sockets – just in case, should they ever fail again.

Just in case you have to do a similar job – here are the EPROM images. Keep in mind, Rev B, 36x 27256 EPROM (sure, you can also use 27C256).
hp 3562a A3 ROM BOARD rev B

And, finally, let’s switch the power on-

All tests passed!

Note – just discovered, someone is offering a spare 3562A ROM board for about USD 100 on xbay…. well, well, but in the end, better a thorough repair, with all EPROM images captured, than just switching some board!

Micro-Tel 1295 Precision Attenuation Measurement Receiver (2nd unit)

Micro-Tel 1295 Precision Attenuation Measurement Receiver: cleaned, painted (!), fixed, modified, and fully adjusted/calibrated

2014/09/21 Simon Leave a comment

The 1295 receiver – before working on the internals, the external parts – the panels – needed a makeover.

(1) Sticky paint removed from side panels, top and bottom panels, using methylated sprits. Imaging scraping off dark green chewing gum, several square feet covered with it. Hope the company that sold this paint is now out of business, that’s what they deserve.

(2) Some more cleaning and sanding, with 400 grit paper.

(3) Primed with self-etching automotive primer. For coating aluminum metal, always use a suitable primer – don’t trust any suggestions on paint cans that it will work without a primer. It won’t.
After some drying, a quick sanding. Not aiming for perfection.

(4) Top coat with a modified alkyd resin. “Hunters green” appears close to the original color shade.

(5) After several hours air-drying, burn-in at about 165 °C, for 60 minutes. This improved adhesion, at least based on my past experience, and no need to wait for days before the instrument can be re-assembled.

(6) Clean the newly painted surfaces with isopropylic alcohol, this gives an even shine, and to confirm that the new paint is fully resistant vs such solvents.

(7) Re-assemble all the small hardware and screws, feets, etc, of the panels!

The other items:

(1) Added filter caps to the YIG driver, when under remote control (more or less a bug in the Micro-Tel circuit).

(2) Added a parallel ot serial converter to the display – the readout values are now transmitted via 2400 baud, via the external control connector. See post in the attenuation measurement section. The circuit involves an ATmega32L which monitors the display for an update, and with every update occurring, it reads out the value, and does the transmission – no handshake.

(3) All frequency related and AFC adjustments, YIG driver adjustments etc. have been performed. Calibration of attenuation levels checked – seems OK – precise calibration, I can only do back in Germany. But seems to be in-spec, and will compare more throughly vs the “master” 1295 – the first unit.

(4) The light of the mains switch, using a T1-1/4 28 V 0.04 V incandescent bulb, with broken filament – replaced by a LED, with an added 1 k resistor in the supply line.

(5) Fitted a spare 2″ display bezel, with red filter – the original one was missing.

That’s the gem, receiving at about 16.260 GHz.

HP 1345A Digital Display

HPAK 1345A Digital Display: a great worry, and a shorted tantalum cap

2014/09/21 Simon Leave a comment

The 1345A is almost a one-of-a-kind, not easily replaced by something else – it is a display unit designed by HP during the early 80s, and used in quite a few instruments that are still of value today. These instruments include various analyzers, e.g., 3577 series network analyzers, 356x series signal analyzers, 4145 semiconductor analyzer, and so on.

it takes in some 16 bit digital data, and converts it into strokes, which are then displayed on an electrostatic (!) CRT.

This repair, I almost wanted to refuse it, because with a description of “dark display”, typically, the CRT is at fault, and there is not much to be done about it – I have a few spare parts here, for the 1345A, but no CRT. My greatest worry, having to deal with things beyond repair.

Well, after some debate, the thing arrived and it has been gathering dust here. Now, I openend it up. Big surprise. The 15 V rail fuse of the 1345A was blown. Took a while to track down which of the various boards was causing the issue. Turns out, the A1 is shorting the rail.
Nothing suspicious was found, so I just left it powered with a current-limited supply, to feel where the power is going. A bit of smell. A 2.2 µF tantalum cap!!

For many other devices, failed caps are a common observation. Not so much for HP equipment, even after 30 years. Quick look at the parts list:

The part specified is a Vishay/Sprague 150D series tantalum cap:

As shown on the datasheet, these are very reliable, the best around. However – these are not the caps found in the 1345A. Maybe, at some point, HP switched to some cheaper tantalums (the 150Ds are about 2 USD each!).

With no axial caps around, all the tantalums were checked, and 1 found defective, 1 suspicious. These were replaced by electrolytic capacitors – good enough.

Red frames: replaced caps, yellow frames: original tantalums, still working.

After putting back a good number of screws, a quick test, and, success!

Needless to say, following the old rule of first checking the power supply rails, and looking for defective caps, is still helpful, although it doesn’t usually help a lot (like in this case) when it comes to test equipment.

EIP 545A Microwave Counter: power meter upgrade

2014/09/20 Simon 28 Comments

This time, not really a repair, but an upgrade.

Every lab or repair shop dealing with really high frequency circuits needs one: a microwave counter. The EIP 54x series has certainly been (and still is) one of the workhorses of the industry. EIP is now Phase Matrix, still selling counters. But I guess, not an easy tasks – there are quite a few of the EIP counters around, and they do have some little issues with tantalum capacitors, etc, but all in all, the EIP counters are really marvelous instruments, rock solid.

The 545A:

In my own shop, there are two 545A counters (18 GHz, N connector), and also a 548A, which is similar, but covers up to 26.5 GHz (3.5 mm connector). The 548A can go to frequencies as high as 110 GHz, with some external mixers. While these have provided good service over the years, they are all lacking ‘option 2’, the build-in power meter. At microwave frequencies, having a combined power meter and counter has a considerable advantage – no need for changing cables, no need for splitters or couplers – just the push of a button. And not always do you want to connect a circuit under test to a valuable 18 GHz+ spectrum analyzer or measurement receiver…

Fortunately, there are clever people around, at the Green Bay Professional Packet Radio club (“GBPPR”), which kindly provide the ROM images and some circuit modification info on the web – to convert a regular 545A, to an option 2 545A!

Well, first we need to collect some parts, a low capacity Schottky diode (HP 5082-2835, 1 pF max.; original EIP circuit uses a different kind, but really any low capacity Schottky will work), a DM8136N (a comparator/address decoder), a 74LS244 buffer, and an AD7524JN (8 bit DAC) – plus, a 10k resistor. Except for the DM8136N, nothing uncommon at all.

The only tricky part, at least here – the 2532 EPROMs. These aren’t accepted by any of the programmers around, and they need a high programming voltage. So first, put together a little programmer that attaches to an ATmega32L, and with the data transfered by USB.

It’s really crude – I don’t anticipate a lot more 2532 EPROMs that need programming, except for the EIP….
I had some 2532A around which are working perfectly fine, just lower programming voltage. The 2532A/2532 – they can be handled by some 2732 programmers, for reading the contents, with a little socket adapter (2532 and 2732 have different pinouts!) – but strangle, the same programmer doesn’t work for writing to the these old beasts.

The second type, they are 2516 EPROMs, no problem with a 2716 programmer.

After fiddling around with the EPROMs, the little programmer, the adapter sockets – a few hours later – that’s now the set of parts:

These are the boards, A105 and A107, with the parts installed – red rectangles: additional parts; yellow: removed parts (resistors R39 and R40).

I would suggest to put all parts in sockets, like EIP did. Then you can change your counter back, to non-option 2, should you ever want to.

After a bit of soldering – that what we have – a working option 2 EIP 545A.

The power meter can be switched off – if you need the extra digits. Typically, I don’t.

All that is left are the original EIP EPROMs, programmed in San Jose, California. Collectables.

Any questions, please let me know!

Micro-Tel 1295 Precision Attenuation Measurement Receiver (2nd unit)

Micro-Tel 1295 Precision Attenuation Measurement Receiver: 2nd unit!!

2014/09/20 Simon Leave a comment

Recently, I haven’t been acquiring a lot of test equpiment, for my own workshop aka museum, because space here in the US is limited, and carrying all these things over to Germany again in 1 or 2 years will be a hazzle. But this time, I could not resist – a Micro-Tel 1295 receiver, for less than 1 ct. per USD 1980s list price! The parts alone, a 2.33 GHz low noise LO, 2-8 GHz Avantek YIG, 8-18 GHz Avantek YIG, a 2-18 GHz broadband coupler, various microwave mixers and attenuators, all of the best mil-spec quality, well worth it.
Also, it will be a great addition to the precision attenuation test set-up: a dedicated receiver each, for the through and reflected power! And, we can safe one coaxial relais (to switch either through power, or reflected power, to a single receiver), and everything will be faster, by almost a factor of 2. The only downside – another PLL will be required, but well, this is just a matter of a rainy weekend.

It arrived well packaged, no damage, except a missing frequency display bezel (which was easy to source, exact fit), but one thing I did not expect: the paintwork on the upper and lower cover, and side panels, has converted into a mixture of honey and chewing gum, a sticky mess, and dark green! So, first task was to strip off this “paint”, which was pretty easy using some methylated spirits, and engage a bit in spray painting. Hunter’s Green.

See the dark green side panel – covered with sticky paint! Now, it is finally clear to me, why the 1st unit, the 1295 acquired earlier, had been re-painted by his former owner….

Note that the lid and side panels have numerous screws and nuts (more than 100 single pieces!) – quite impressive, how little Micro-Tel had to consider manufacturing cost!

One issue found so far: the IF distribution relais had some intermittent noise – most likely a bad contact somewhere. So took out all the board, cleaned up the edge connectors (all gold plated), and moved the connectors around a few times – and, the issue is gone.

A note on edge connector cleaning: this is best done, from my experience, we some special type of eraser. Don’t use anything harsh, abrasive, or natural rubber. It will either scratch it gold coating, or leave traces of residue behind that isn’t going to improve contact resistance and reliability.
Best suited at vinyl erasers made especially for PET film or tracing paper. Prismacolor Magic Rub.

These crumble a bit, but the vinyl materials absorbs all the dirt, and can be brushed of easily, with an ESD brush.

The unit is overall very clean, just the frequency calibration/display seems to be quite a bit off. This will be the next step, after a thorough warm up.

And, as for the first unit, I will add a parallel to serial converter for the display, same as for my main Micro-Tel 1295, because I don’t want to use the IEEE-488 bus for this device. It will have the same 2400 baud (TTL-level) serial output. Also, a little capacitor will be added, to limit the bandwidth of the Freq Control/YIG driver amp when in external mode – this seems kind of a bug of this device, because the larger bandwidth only increases noise, and the receiver is not build for fast sweeping anyway.

SimonsDialogs

Category Archives: Test Equipment Repairs

Micro-Tel MSR-904A Microwave Receiver: the monitor output

Micro-Tel MSR-904A: RF tuner block diagram and component specs

Micro-Tel MSR-904A: some basic repairs

Micro-Tel MSR-904A Microwave Receiver: the big box arrived!

3562A Dynamic Signal Analyzer: LCD retrofit NewScope-5

3562A Dynamic Signal Analyzer: EROMS fixed, finally!

Micro-Tel 1295 Precision Attenuation Measurement Receiver: cleaned, painted (!), fixed, modified, and fully adjusted/calibrated

HPAK 1345A Digital Display: a great worry, and a shorted tantalum cap

EIP 545A Microwave Counter: power meter upgrade

Micro-Tel 1295 Precision Attenuation Measurement Receiver: 2nd unit!!

SimonsDialogs – A wild collection of random thoughts, observations and learnings. Presented by Simon.