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Motorola 2N5160 PNP RF Transistors: new-old-stock, medium old stock, fake stock?

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Some of the 1980s, 1990s pulse and signal generators use push-pull power amp stages to provide output levels of +-10 V into 50 Ohms, and similar. These are often discrete circuits, utilizing PNP-NPN small power transistors. While the NPN types are still widely available, there used to be some shortages of 2N5160 PNP transistors. Recently, there are are many offers for “Motorola” branded parts, with datecodes from about 1998 (K98xx) to about 2004 (K04xx). In contrast to the earlier Motorola parts (Rxxxx date codes), these have shiny cases. It is quite unlikely that Motorola actually manufactured RF metal can transistors in 2004… (1999 onwards, Motorola no longer made transistors, but transferred the business to ON Semiconductors).

Strangely, the cans have “KOREAN” stamped into them, in various styles and sizes. Would a fake producer have stock of many different kinds of fake cans? Or did ON Semi produce these parts with some existing stock from the 1990s? Many semiconductor producers actually have decade old wafers in stock that they package whenever there is a need.

Let’s have a closer study. Unfortunately, no electron microscope here. But we do our best. Here the die of the defective HP branded original Motorola part. Red arrow shows the burn mark, defect area.

I sacrificed one of the 0.7 USD suspicious parts with K0439 datecode. To my great surprise, they are exactly identical in die, bonding method, and die attachment method.

A quick function test – put the new K0439 date code 2N5190 into an 5 MHz power amplifier. And working just great at >20 dB gain and about 1 Watt output.

Further, we study the collector-base capacitance, at -28 Volts bias U_CB (note that some datasheets specify “28 Volts U_CB” but this won’t work with a PNP transistor – it is conducting like a diode in C-B, if the collector is positive vs. base).

A test with the trusty HP 4192A, and 2.5 pF measures. Exactly the typical value. Also checked one of the certainly genuine Rxxxx date code transistors, and this measured at about 2.7 pF.

Test done at 1 MHz, and calibrated the 4192A with open and short.

So far, so good. All I can say is that these transistors are good 2N5160, whoever made them.

Various

A low frequency xtal oscillator: Austrian generosity, gold, and crystals

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A while ago, an Austrian fellow contacted me for some collectibles, long-range telephone line filters (from carrier multiplex phone lines). Many decades ago, phone lines were used at some 50-100 kHz frequencies, to transmit several (!) calls per wire pair. This required good filter, quartz filters were commonly used.

These are 4-electrode filters that are held only by 4 wires soldered to it. Probably oscillating in some flexing mode.

The electrodes are normally connected diagonally, and with a few resistors and an amplifier, I got the part to oscillate nicely. Be aware that you can’t feed a lot of power to these crystals, so it needs a rather high impedance oscillator circuit.

Resonance is at about 50 kHz.

Also connected the specimen to a HP 3562A analyzer, in swept frequency mode, and good nice response plots. There is another dip at 100 kHz!

The schematic, pretty simple, using a 74HCU04 unbuffered inverter, it is a very handy circuit, and years ago I got several tubes of these… you may use any other type of amplifier, gate, or even transistor circuit to get any such xtal oscillating.

Also did some some study on the temperature effect – heated to 100 degC, the frequency dropped by 200 Hz!

Various

HP 8753C Network Analyzer: a new old YTO, and a new old firmware

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After another trip to Germany, another HP 8753C to fix. This unit had option 020, 006, a 6 GHz unit, but there is no 6 GHz test set.

First, we need to get a suitable YTO, found a good ASF-8751M, from Israel. Cleaned it up and gave it a proper test.

It is a 4-8 GHz unit, but I easily got good power down to necessary 3.6 GHz. It is a well-behaved unit, with reasonable power consumption running of +15 and -5 Volts. The heater may be better run with 24 Volts, but there is only 15 Volts in the 8753C, and it is good enough it seems.

Some modification of the PLL board, as described before, to approximately double the tuning current, installed a 20 Ohms sense resistor, and installed a BD249C transistor on a good heatsink.

A quick drawing of the heatsink, should you need it. Use 1 mm aluminum sheet. Don’t cut yourself, when cutting the metal!

The YTO, installed in the veritable source assembly. Pretty confident that this will last for a while.

This time, all worked well and the pretune correction functioned immediately, no further adjustments needed. Phase lock seems very stable at all frequencies, scan rates, and band transitions.

Out of curiosity, did a phase noise test of the 8753C in CW mode (fixed frequency mode), getting well below 100 dBc. Pretty good. Maybe better than the original YTO.

For the current unit, I also wanted to update the firmware, and install the 010 option (time domain analysis). The option installation (and EEPROM backup), done like described in an earlier post, but desoldering the EEPROM, and changing three bytes…

The unit is still running pretty old firmware.

Should be easy enough to program some 27010 EPROMs, but the devil is in the detail. After a number of incorrectly programmed EPROM, finally figured out the once of the CD4015 CMOS of the EPROMMER had failed! Fortunately, I had some in stock to fix it.

After these efforts, the 8753C is starting up with the latest (albeit, dated) firmware, and all options.

A few tests with filters and such, a very useful and well working unit. The CRT also very good, no need to install a LCD.

Various

HP 3325B Synthesizer/Function Generator: a quick fix, and a hot transistor

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Recently, I got a defective HP 3325B, it is a very useful generator even for today’s standard. It features some highly linear ramps, has great frequency resolution and a powerful output (10 Volts p-p into 50 Ohm). This unit reportedly had major issues, no output, and failures with startup. So even before switching it on, I removed the panels to check. Nothing obvious at first glance.

After a quick power on, some smell from the output section, and clearly, there are some burned resistors, and one of the power stage transistor is terribly hot, so hot that the solder melts… don’t burn you fingers!

Removed the board altogether (take care not to damage the connection flat cables!), and even the solder had some spray by heat effect, so I cleaned the area well.

To get access to the resistors, and to also do a proper test, all the transistors in the area were removed, and the transistors desoldered. All cleaned up pretty well, the board seems to be of good quality.

The 3-440 transistor aka 1853-0440, cut open. It has a tiny chip, difficult to see the damage with my means, but it is shorted to base.

The resistors, the only issue is a slightly discolored 47 Ohms carbon composition resistor, part EB4701, a 0.5, 10% tolerance resistor. Quite expensive to get, and the part, despite some signs of heat, tested good and within tolerance. So I decided not to replace this transistor, because it has an effect on the high frequency performance of the circuit.

The power amp, it is a marvelous push-pull design. It relies on complimentary NPN-PNP transistors that have high frequency power.

Nowadays, the PNP RF transistors of this sort are rare, probably they even were rare and expensive during their time.

The damaged resistors, fortunately, after a good amount of searching, I found the bags here in by temporary Japanese workshop.

The transistors, these 3-440 are equivalent to the 2N5160, and I happened to have 3 of these back in Germany, new old stock. Purchased them some years back, because they are generally not easy to get.

After these replacements, I run the adjustments and performance checks as per service manual, with no trouble at all. Also the self test passes flawlessly. We can call the generator fixed.

Out of curiosity, I checked with ebay, and there are very reasonable offers of what appear to be Chinese copies of 2N5160 transistors. They have the Motorola label, but to my knowledge, the date code is much past the obsolescence of these parts at Motorola. So I am waiting to receive these parts, and will give them a good test and study, to see if these are good replacements, or just fake.

HP 8662A Synthesized Signal Generator

HP 33321SB aka 33321-60026 Attenuator: HP 8662A Synthesized Signal Generator fix

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Finally, I received the attenuator set for the HP 8662A repair. The very special 5+40+40 db attenuator with a side connector (rather than the usual design of these attenuators with two top SMA connectors).
However, a quick test showed that the 5 dB step is not working right. The “through” path is fine, but when I engage the 5 dB attenuator, is is something like 45 dB, unstable. Maybe a blown segment? That would be an easy fix.

So, I opened it up carefully, and found a broken contact. It seems the side connection is pushing a bit on the contact, and over the year, this design caused the plastic to fail. Tough to fix without precision drills and machine tools. So it will need to wait for the virus to clear, and for me to go to the German workshop again, to attempt an repair.

There are two small plastic studs, and they broke off, maybe the plastic got brittle over time with the pressure of the side contact pushing.
Let’s think about how to fix it, if at all possible.

Note – the seller was kind enough to refund half of the price, without having me to ship back the part, fair enough. At least some spare coils and segments should I need to fix other attenuators in the future.

HP 8566B Spectrum Analyzer

HP 85662A Spectrum Analyzer Display: a quick fix of the 120 V power supply

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A 85662A spectrum analyzer display for repair, the symptom (I didn’t take a picture) – a green square in the middle of the CRT -some lines are visible within, but no proper display. So, acceleration, CRT, and focus seem good – at least it seems to be a manageable fault rather. Maybe something with the XY deflection amplifiers – but why would both fail at the same time? In any case, first things first and checked the power supply. All the LEDs are on, on the power supply boards, but there is no output on the 120 VDC supply (well, some output, like 7 VDC) – the supply that is essential for the deflection system to work.

Some study of the schematic of the A1A7 assembly. Note that the voltages differ with the serial, this is a 85662-60235 part number board. Q7 is a current source that is driving the main transistor, Q8. If the voltage is trending higher, some of the Q7 current will be shunted to ground through U2.

It is a bit troublesome and dangerous to work on the life circuit (about 150 VDC at the input!). So, I did a check of all the transistors with a diode tester – and found the B-C junction of Q5 shorted. A HP part 1854-0019.

Some study of cross-reference lists, the 1854-0019 is a simple 2N2369A, found some in the basement parts storage (even a military rated and tested JANTX2369A with golden legs!).

Still, even with this fixed, no success. Further to other parts – replaced the green parts in the picture, an LM301 opamp, and another transistor, with no luck. Finally, soldered a few wires to the board and did careful checked in the circuit with power on, it can’t be helped otherwise it seems.

A few minutes later – the failure found. The Q7 current source is not giving any current, the base of Q7 is not biased properly. An open 110 kOhm resistor! It is quite rare to find defective resistors in HP equipment, but especially high value resistors running at higher voltage are prone to aging and failure, eventually.

With a simple, new resistor added, a metal film 110 kOhm, the supply is working again, and so is the 85662A.

Various

HP 6205C Dual DC Power Supply: a generous binding posts fix

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The repair itself, it is not particularly noteworthy, because this supply has served me well in the last years, in fact, it had been switched “ON” all the time to power an experimental setup.
The initial repair of this supply has been documented before, and on the pictures there it is quite visible that this supply had damaged binding posts. Seems that the prior user dropped it on the front panel.

Now the noteworthy facts, a kind reader of this blog, an American fellow, had a few of these posts at hand, from a HP plotter. He kindly sent them to me, free of charge!

So, as a result of the kindness of the reader, and the standardization of the parts HP used in their equipment, the power supply is now in better shape than ever before.

Did a few tests, like, checking ripple current at full load, and electrical safety – ground resistance, but all looking good.

HP 8662A Synthesized Signal Generator

HP 8662A Synthesized Signal Generator: almost fixed!

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Still working on the 8662A, a unit that is in very good shape but someone tampered with the power supply in a non-expert attempt to fix it.

After a little bit of waiting, CMOS ICs worth a few dollars arrived, and a single 4049 CMOS fixed the power supply. Probably, the defective caps on the power converter board destroyed one of the transistors, and then lead to a voltage spike that destroyed the CMOS (which has a connection to the sense line) – only that gate got destroyed, the other gates still work.

There was no need for any adjustments, the voltages are still accurate to the resolution of the meters I have around here.

Back up and running, the machine is working fine and giving good output. At least after installing a coax line to bridge the missing attenuator.

There are some small issues that were easily fixed. A few non reactive keys that were traced to a bad contact of the connector related to one of the lines of the key matrix.

… and some issues of the modulation display. It is stuck at “20”, but the 1st digit (+-1) is working. Turned out to be a defective trace of the multilayer motherboard. Maybe someone damaged it by pulling on the ribbon cable, or similar bad handling – it is one of the outermost pins.

Easily fixed with a wire and some silicon glue.

Some study on the attenuator – to my great surprise, the 8662A uses a retrofit set, to replace the obsolete attenuator at the time of construction of this very late production unit. And, it does not(!) use the attenuators of the 8663A. These don’t fit, neither in values nor in size, because there is an interference of one of the SMA connectors with the bandpass filter that is also mounted to the inner front plate. The missing attenuator, a 33321-60026 is a 85 dB unit, one segment 5 dB, two segments 40 dB each – these are switched simultaneously. A really special part, and difficult to assemble even if you have several other step attenuators because of the length of the 40 dB chip…

I don’t actually need to attenuator that much, but luckily found this set on ebay from a seller in Israel. The kind guy offered it for a very reasonable price, great! So we can restore the unit to full function.

Meanwhile, the attenuator set has arrived in Germany, where I will pick it up during the next business trip – coming up soon. In any case, I will also need to pick up numerous screws, because the unit arrived with several screws missing, even some quite essential ones.

Anyway, there are plenty of HP screws around.

Various

HP 8753C Network Analyzer: Serial numbers, options, EEPROMs

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The HP 8753C comes with some software options 010, time domain (essentially, a built-in FFT function), and the even more useful harmonic analysis, option 002. These work without any further calibration, and used to be available as a code to enter to the instrument , with service function 56, to update the option status.

Thanks to a kind gentleman, such codes are available now, and normally you can add them to the 8753C without any expert knowledge and risk.

Unfortunately, for this instrument, the method to add options by code entry didn’t work. How come? As much as we know, the option code depends on the serial number, let’s check if the serial of the CPU board is the same as that of the instrument (ending in 00860). A first hurdle, how to read the serial – it is not showing upon startup for the 8753C, but you can get it by first executing service function 55, which will fail, and then go to Display-Title.

To my big surprise, the serial shown is incorrect, only 4 digits, missing the “8”.

Accordingly, we need to dig deeper, and the serial number and other information is stored on the U23 EEPROM, a 2kByte chip, Xicor.

It is a very long lasting device, no reason to believe that it will fail anytime soon, but there are always risks. First, I read all the coefficients via GPIB, and then carefully desoldered the chip.

Actually, desoldering went very well, even just with plain tools, a soldering iron and a manual solder sucker.

The programmer, put together from a few jumper cables, and an ATMEGA128A board. When reading, I hardwired the WE- write enable input to VCC, to make sure that no data are lost. There are also 6k8 pull ups directly on the ZIF socket, to make sure the input stays “High” even if the jumper wire is not connected well.

In the EEPROM, clearly there is the incorrect serial, it is not actually missing a digit, but has an incorrect character. Maybe it got modified when the CPU clock failed (remember that this board had a bad osciallator?

Now, we need to put in a single character, an “8”.

I don’t normally need to program 2816 EEPROMs, so rather than taking chances with some incompatible programmers, I made a small program, to just set a single byte, at a given address. In this case, writing an “8”.

With the serial number corrected, put the EEPROM back onto the CPU board – using a precision socket.

Using the secret code that only works with the matching serial – and with the write protection of the CPU board disabled – the option install worked perfectly fine.

Now, the 8753C shows the options upon startup, and the time domain and harmonic analysis functions show up in the menu as softkeys.

Afterwards, I checked the EEPROM contents again, there are only 3 bytes changed, in-line with what can be found in online forums. Also tried to activate the 006 6 Ghz option, not much use for me, but the option code is same as seen for the 8753D, etc. There are 3 bytes, right in front of the serial, with the upper half-byte bits all set (0xFx), and the lower half-byte encoding the options in a bit-wise fashion. With no options, the three option bytes are all zeros 0x00.

If you need any of these EEPROMs or related advise with the 8753x units, just drop me a line.

LCR Meters

HP 4192A LF Impedance Analyer: a few final fixes, and 14(!) EPROMs copied

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Finalizing some repairs on the 4192A – there were two tasks remaining, replacing one of the front buttons that were damaged, and making a copy of the EPROMs, because none could be found in the web and the various forums.
The EPROMS are MB2516 type, 1982 vintage, with a white ceramic package and gold pins. Better not damage them, so I removed them after good sleep and after a cup of coffee, using some good tools.

Reading such old EPROMs can be a bit tricky with modern programmers, so I didn’t want to take chances and used a custom reader, reading every address several time. No uncertainties showed up, all reads identical.

The serial, suggesting 1981- vintage. According to the date codes, made in about 1982.

Just in case you need a copy, see here, hp4192_eprom.

Next, the defective button (at the left display) – did a thorough search in the German workshop, but no such button around (a dark brown, LED type button cap). But I did find a “LCL” labeled button. The original 4192A “Local” button has no print, so I did a little swap as indicated on the picture. Now all looking good.

To handle all the data and sweep function of the 4192A, best to use it in combination with some software. Fortunately, there are some great tools available for free, working right out of the box.

A set of resistors, left side are my 0.01% precision resistors (using them for calibration and adjustments of LCR meters), Vishay S102C/S102K, AE (Alpha Electronic) XT series. Next to it, some other resistors, all 1 kOhm.

The precision 1k resistor…

A 68 nF ceramic cap…

1 k low cost axial resistor…

1 k standard good quality metal film axial…

1 k metal oxide 4 Watt resistor (green, POS400 Vitrohm series) …

All in all, the 1 k resistors have very little parasitics up to 13 MHz, say less than 1 pF parallel capacity, and inductance, below what can be reliably measured.