EEVblog #540 - HP35670A DSA Repair - Part 3

[EEVblog]

More progress (or is it?) on the HP35670A DSA repair.
Part 2:
Part 1:

[vaualbus]

The first thingh you could do is replace all the op amp equals to the broken ic.
Secondly If I were you I would try to repair the source circuitary first and than from there see.
The overload protection can be cause by the fact that the two coaxial cable from the attenuator board aren't connect to the analog board.
On the anlog board the voltages are right so I will not worry about that board.
Probably the other ics aren't break at least the analog switches (DGxxx part) aren't beak because they work at five volt for the digital part and probably accept probably more than -19v to input.
The good news  is that the asic is definitly work because they drive the reference voltages as the dacs (on the source the othere is the for the reference voltages).
By now you should try to repost the blog in HP forum this time asking for the analog board problems.
Post also in Agilent/Hp yahoo group.
Wish for a next video.
Best regards, Alberto

[nitro2k01]

That "sine" looks like one or more of the bits, including the most significant one, are faulty (ie held constant). The question is if that fault is in the DAC itself or in the FPGA (or otherwise outside the DAC chip.) There's a DAC near the voltage reference. Is that DAC setting the voltage reference, or is it using it? If the latter, is there a second voltage reference near the output DAC you can try doing something about?

The reversed polarity of the reference TP's are obviously suspicious. Maybe try tracing that back through the components and see if gives you something useful. My theory is that they're both generated from the same reference somewhere, and one is inverted through the opamp. But the actual reference is blown, such that it output a voltage of the opposite polarity compared to the expected value. And then that creates the faulty test point values.

But yeah, this is starting to look like beyond economical repair. Maybe one of the in/outputs of the unit received a large negative voltage which leaked into the negative rail through protection diodes and destroyed everything in its way on the negative side.

[qczech]

Hi Dave.

Maybe it is possible to obtain the schematics from someone who worked on the instrument? Might be worth asking if you have some friends in Agilent.

I've found the Supplemental Operator's Guide and googling the name that appears on the first page I've got this: David Forrest. There is a phone and an email. Might be worth a shot.

Kind regards.

[nitro2k01]

Probably the other ics aren't break at least the analog switches (DGxxx part) aren't beak because they work at five volt for the digital part and probably accept probably more than -19v to input.

The DGxxx switches will have internal protection diodes, so operation outside the voltage rails is not recommended

The good news  is that the asic is definitly work because they drive the reference voltages as the dacs (on the source the othere is the for the reference voltages).

I think it's too early to tell. What you can tell is that the voltage is set once, but not for sure if the value is correct or not. The fact that the polarity on the test pins is inverted, and also 0.3 V off suggests that the reference DAC *might* be giving a false value. The signal DAC is giving a lot of incorrect values. Maybe the reference DAC is giving one such incorrect value, but is never updated again so you can't see it as clearly as with the signal DAC.

[vaualbus]

Or maybe there is another opamp before that are blown.
Yah if the source dac use the same reference voltage it could be that. But If the fpga is blown at all the reference voltage isn't there. The voltage is produced by a dac controled by the fpga. Look at the block diagram. So my guess is to track that ref voltage and see if after the dac pass through a opamp.
It could be the case that the dac ouput is ok but that then signal pass through some active filter to make the sine wave.

[Fagear]

You have good oscilloscope (not one of them), PCB is not too complex. Output BNC is at 15 volts, that is leading thoughts to one opamp pulling its output to positive rail. Because it has failed or component before it has. Why just not probe all signal pins of all opamps (only three of them per amp) in that area ? It's not so big! Try to trace path from ouput BNC to DAC at first.
Then you can deal with DAC if it still will be outputting some garbage.

[EEVblog]

Why just not probe all signal pins of all opamps (only three of them per amp) in that area ? It's not so big!

Because it's stuck inside the box!
I really need an extender card or cable before I can properly work on this any further.

[vaualbus]

you culd to download all the datasheet for the opamps and see which have the lower range to +-15, couple have +-18 and theoricly they are ok (+19 + 15 = almost 34).
I've reseen the video and at least I've see another opamp with the same hp number so also them will be wrong.
At this point the best way is to fix the source. For my point of view the output dac is ok, the signal is than passed through a active high pass fileter to make the sine wave, if the op fail of course you will see that signal. At list I have see a test point call adc ini, put a signa in the instrument and see If the signal arrive at that pin If not see If the signa arrive at the two coaxial cable and than try to track the signal.
I think I've found the main ADC is an MC1405 but I'm sure. it is near the voltage reference circuitary. 
I suppose that the attenuator board are ok indeed, there isn't regulator problem on it.
Why you not make an extender connector?
Best regards, Alberto

[SeanB]

Why just not probe all signal pins of all opamps (only three of them per amp) in that area ? It's not so big!

Because it's stuck inside the box!
I really need an extender card or cable before I can properly work on this any further.

Stick a tone on the connector to the board and look for it on the board with a tracer . Works well to find the pin, then simply check the opamp with diode test and see if the output is stuck. Simple enough to do to all the opamps to see if any have dead output stages.

[Rutger]

Stick a tone on the connector to the board and look for it on the board with a tracer . Works well to find the pin, then simply check the opamp with diode test and see if the output is stuck. Simple enough to do to all the opamps to see if any have dead output stages.

Yes, can't you take the board out and power it with an external supply? Then you can follow the signals with a scope.

[nikifena]

Hi, Dave
Power the board with external power suppply. Power just these +-15VDC for the opamps

Than using a multimeter read the voltages of each opamp - positive and negative inputs and the output. You know how the opamp works, so maybe you will find something unusual BEFORE desoldering all of the chips there.


Niki

[aaronsnoswell]

Hi all. Sorry if this question is obvious to the non-beginners out there. Around 5:04 (and later on) in the video, you can see a close up of the point where one of the coax connectors is. There is some odd looking silver disk behind the coax connector. What is the purpose of this component - it looks a bit like a small battery?

Really really enjoying this video series, by the way - keep it up, Dave!

[bktemp]

As I had said in the other thread: I don't think the opamp died from overvoltage, more likely it was a reverse voltage from the negative supply missing. Then the inputs (at GND level) are the most negative voltage which can easily damage the input stage because the input voltage of most opamps is limited to the supply voltage rail (or a little bit beyond).
The same applies to most other ICs connected to the -15V rail. I would also check the ADGxxx ICs. Some of them don't like if not all supply rails are powered.

It looks not very promising, but it is a great opportunity to make a series of repair videos. Especially showing how to repair stuff without having the exact schematic.
I would start with the DAC, because ist is partially working: You know how the sinewave should look like at the output and input, go through the digital input signals and check where they come from. Either the DAC or some logic driving the DAC seems to be damaged.

[SeanB]

Hi all. Sorry if this question is obvious to the non-beginners out there. Around 5:04 (and later on) in the video, you can see a close up of the point where one of the coax connectors is. There is some odd looking silver disk behind the coax connector. What is the purpose of this component - it looks a bit like a small battery?

Really really enjoying this video series, by the way - keep it up, Dave!

That is a PTC fuse to protect the outputs from being accidentally fed a large signal. Hopefully the PTC will heat up fast enough and go high resistance to limit the current flowing into the outputs. there are large clamp diodes there to enable this to happen without killing the opamp driving the output. Same as the PTC in your meter ( hopefully) protecting the inputs from overvoltage.

[Nermash]

In previous dsa Dave repaired that was the 50 ohm terminator IIRC.

[Napalm2002]

If the cost of the opamps are cheap enough it may be worth throwing a handful in and shot gunning it so to speak.

[pickle9000]

Swapping out a pile of chips is a valid method but is fairly heavy handed. A board extender would be very nice to help for testing (the op amps). I'd probably swap out 2-3 questionable chips at a time then test and hope I get lucky, still pretty heavy handed.

A schematic makes life so much easier, but unless you plan on repairing these for a living hardly worth drawing it out.

[LaurenceW]

... I think the real cost issue here is not a handful of op-amps (and the odd unobtainable esoteric IC), but Dave's time!

Yes, I concur that that "sine wave" (looked more like a porcupine wave!) could be stuck bits. Are these available, between the ADC chip and a counter/latch/buffer, or all internal to the ADC?

[EEVblog]

A board extender would be very nice to help for testing (the op amps).

A board extender is pretty much essential at this point.

[Rasz]

you talk about sucking chips up - that is time consuming
setup your hot air to be under the board heating solder joints, then you can swap chips for sockets in a matter of seconds without playing with individual holes and solder wick

[poorchava]

The bright side of the whole situation is that only FPGA and the Raytheon chip (what does it do anyway?)  seem to be unobtanium.  I'd try to stick a logic analyzer on the bus between FPGA and DAC to see if the data sent to DAC resembles a sine.  If not,  then most likely the FPGA is blown and you're screwed.  Otherwise it seems reperable.

[Noize]

A board extender would be very nice to help for testing (the op amps).

A board extender is pretty much essential at this point.

If you do get/make board extender maybe you can use that AIM TTI Current probe that you reviewed to quickly find out what op-amps etc are buggered?
I assume you still have that probe.

[alm]

A thermal camera would probably be easier if the opamp is drawing excessive power.

[daddario]

A thermal camera would probably be easier if the opamp is drawing excessive power.

I don't think Noize was suggesting excessive power consumption, but rather finding an opamp that's an 'odd-one-out'.
i.e. no supply current at all, an unequal current between rails or some kind of a third option that stands out from all of the other opas.

[adcurtin]

I gotta recommend the Hakko 808 desoldering gun. If you chose to go the route of replacing all the op amps, I'd bet you could have all 15 on that board replaced in an hour. Seriously, this thing is absolutely awesome for anything through hole.

[wbooth.clearscene]

It may be worth thinking about this from a different angle. Why is it the 15 grand replacement power supply failed? Figure this out and you could be on the way to unravel the cause of all the other symptoms your seeing. Eg a simple shorting problem on the main board takes out the supply, but that problem could screw with reference generation, etc... Worth a shot before calling it a day.

[Zad]

Given the silkscreen claims on the board, I would do a sanity check on those +/- voltage levels. Is there continuity on the pin with a positive voltage, to the positive supply pins on the op-amps? It may be that the silkscreen really is mis-printed, but there may be a reason further down the chain that the voltages have swapped.

Consider removing the panel and applying a +/- supply to the op-amp power feeds, inject a small signal to the inputs and measure the outputs. That should give you an indication of which (if any) have failed, without having to power up the digital side etc.

Tack a ribbon cable to the input pins of the DAC, and bring them out to the scope. We aren't talking about 100MHz signals so you should be able to get some indication of what is being generated while the board is active.

[tri-be]

The DAC at U2 (AD565AJD,  which I presume is for the front panel Source output) is fed by the two TTL serial to parallel ICs (74HC595) at U1 and U17. U1 provides the most significant 8 bits to the DAC. The 'scoped sine wave is repetitive which at least suggests the serial data is OK. It's possible that one of U1 or U17 is damaged such that the output enable is not working, so the "steppy" output might be due to that (U17 handles the least significant bits of the DAC,  so it would most likely be that IC in that situation). I would somewhat expect U17 to be the cascaded output of the U1 device, the serial data being sent least significant bit first from the digital board.

However, the DAC datasheet says it is powered up to +/- 18V, so I would guess it's powered from the same +/- 15V supply as the dead op-amp, and I would suggest that it is actually fried.

You could probe/scope the digital inputs of the DAC to see if they all (or at least the lower bits) change on sine wave generation, and directly scope the output of the dac on pin 9.

I think if the DAC is dead, there would be no dishonour on giving up on this.

[Psi]

At this point i would probably replace all of the opamps on the board at once.

[azi]

The extender to allow more testing would be a good next move, but lacking that, I would desolder the opamps one by one and test them on a breadboard to see if they work. If many have failed, then I would replace all of the semiconductors on the +/- 15 volt rails. Hopefully, the +5 volt chips are all ok.

[Rasz]

AD565AJD
I think if the DAC is dead, there would be no dishonour on giving up on this.

AD565AJD is $10 with free shipping

[EEVblog]

If many have failed, then I would replace all of the semiconductors on the +/- 15 volt rails

That's about 25 opamps, and a handful of chips, minimum, on that one board.
And that doesn't take into account almost certainly failures on the analog input board as well.

[Jonny]

Make your own card bus extender

http://nz.mouser.com/ProductDetail/AVX-Connectors/108457096002025/?qs=sGAEpiMZZMud62t8luTOJtxE%252bQ%2fcV%2fAVEzdlj0dzMv4%3d

Cheap as chips! And I'm sure you'll have contacts that would make a one-off pcb for it 

I can sympathize with the groans associated with getting so far and wanting to do more but not knowing if it'll be worth it.... been there.

Top effort so far 

[Fagear]

Because it's stuck inside the box!
I really need an extender card or cable before I can properly work on this any further.

So why not just solder three wires by each opamp (or clip some hooks on it) and slide the board in? Just as you did with test points and alligator clips? You can see everything on each of them by scope. Its something about 5-10 minutes to sold wires, slide board in, power it up and probe with your scope!

Given the silkscreen claims on the board, I would do a sanity check on those +/- voltage levels. Is there continuity on the pin with a positive voltage, to the positive supply pins on the op-amps? It may be that the silkscreen really is mis-printed, but there may be a reason further down the chain that the voltages have swapped.

Its a good thing to check this. But this voltage is not feeding opamps, they are on +-15 volts. Not so easy to check by opamps pinout. As service manual says - it is used as reference voltage by ADC. If ADC is in that ASIC you don't know its pinout and cannot correctly probe some pins.

Consider removing the panel and applying a +/- supply to the op-amp power feeds, inject a small signal to the inputs and measure the outputs. That should give you an indication of which (if any) have failed, without having to power up the digital side etc.

I don't think it's a good idea. Some mixed chips (that are digital+analog and use separated power supplies) don't like situation when one supply is on and other is off. For example - PGA2311 audio volume control IC. It starts to overheat if you apply +-analog voltage and do not apply digital power to it. I think soldering some wires and put the board back is better solution.

One thing I noticed in service manual (I have three versions of them now): in the table "Functional Tests All Self-Test Group" it says that A5 board is doing something with IIC bus. And there was error message on the screen about it. I suspect digital control board is sending data through A5 board to the DAC via this bus. If there is something wrong with it it can corrupt some messages causing such weird output from the DAC.

[Flump]

I cant offer any words of wisdom as fixing this is
way out of my league but i hope you dont give up on it,
maybe have a break from it, and attack it at a later date
armed with some new ideas and hopefully a schematic
will turn up.

[daddario]

So why not just solder three wires by each opamp (or clip some hooks on it) and slide the board in? Just as you did with test points and alligator clips? You can see everything on each of them by scope. Its something about 5-10 minutes to sold wires, slide board in, power it up and probe with your scope!

I've used this method and with such a large number of required test points the wire soldering takes up far more time. Plus having just a bunch of wires on your bench instead of a board to measure is absolutely unintuitive, especially if you don't have a schematic and the board layout is the only thing to rely on. The only recommendation I can give in this kind of a situation is to use a ribbon cable with one end terminated with an IDC connector and the other end(s) soldered to the needed test points. This way you'll have this monolithic multipin from where to measure and this helps to keep things a little bit less messy and confusing.

[rs20]

Working atop nitro2k01's great suggestion that some of the DAC's input pins are stuck high or low, I tried simulating this in MATLAB. Forcing certain bits on or off didn't quit produce the right output (in particular, the signal would show frequent excursion to fullscale high and low, which you don't see here). But, long story short, if you simulate that the DAC has failed in such a way that it just sums all the input bits and just outputs that sum (outputting b1 + b2 + b3... instead of 1 * b1 + 2 * b2 + 4 * b3...), you get a very familiar looking graph (attached).

This doesn't feel like good news for the state of health of the DAC, although it is circumstantial evidence at best.

Source:

% Random tweaking value
dacbits = 13;

% Ideal sine wave
y=sin(0:0.0003:2*pi);

% Values to DAC
vals= repmat(uint16(y*(2^(dacbits-1)-1)+(2^(dacbits-1))), 16, 1);

% Convert into individual bits (from LSB to MSB)
bits = 0 ~= bitand(vals, repmat(uint16(2.^((0:15)')), 1, numel(y)));

% Simply sum all the bits, instead of do a sum weighted by 1 (LSB) ... 2^N
% (MSB)
plot(sum(bits))

As a side question, I'm wondering if this idea makes any sense: I'd go around and test the voltage across the op-amp inputs (input- vs input+). According to the whole virtual earth principle thing, they should be equal (unless the output is saturated). If you found just one or two op-amps that failed VEP, maybe it would be worth a shot at socketing+replacing those. This obviously requires you to be able to probe the live board, though.

[vaualbus]

It not make a lot of sense because the point where dave measure the strange signal is not the dac output but is a point mark 1 pass filter. On the output of the dac a signal that seem a sine wave apper. I think is made in that wave and than pass through an active filter to clean and make the sine wave so If the ic is break no signal pass or some noise.

[Anks]

I think that the bits are probably not reaching the required level to switch them in and maybe cause by the reference voltages or even line contention.

[RupertGo]

I'd so walk away from this one.

[EEVblog]

So why not just solder three wires by each opamp (or clip some hooks on it) and slide the board in? Just as you did with test points and alligator clips? You can see everything on each of them by scope. Its something about 5-10 minutes to sold wires, slide board in, power it up and probe with your scope!

Because it would be a ridiculous mess. There are at least 25 opamps on this board alone, not to mention the DAC, ASIC, MUXes and other points.

[EEVblog]

I'd so walk away from this one.

At this point normally I likely would too, but it will make for some more interesting troubleshooting videos I think.
Just don't expect it to work at the end of it...

[c4757p]

Rather than wire up every single op amp, why not take the time to wire up an extender?

[EEVblog]

Working atop nitro2k01's great suggestion that some of the DAC's input pins are stuck high or low, I tried simulating this in MATLAB. Forcing certain bits on or off didn't quit produce the right output (in particular, the signal would show frequent excursion to fullscale high and low, which you don't see here). But, long story short, if you simulate that the DAC has failed in such a way that it just sums all the input bits and just outputs that sum (outputting b1 + b2 + b3... instead of 1 * b1 + 2 * b2 + 4 * b3...), you get a very familiar looking graph (attached).
This doesn't feel like good news for the state of health of the DAC, although it is circumstantial evidence at best.

Nice work!

[Stonent]

Given the silkscreen claims on the board, I would do a sanity check on those +/- voltage levels. Is there continuity on the pin with a positive voltage, to the positive supply pins on the op-amps? It may be that the silkscreen really is mis-printed, but there may be a reason further down the chain that the voltages have swapped.

Consider removing the panel and applying a +/- supply to the op-amp power feeds, inject a small signal to the inputs and measure the outputs. That should give you an indication of which (if any) have failed, without having to power up the digital side etc.

Tack a ribbon cable to the input pins of the DAC, and bring them out to the scope. We aren't talking about 100MHz signals so you should be able to get some indication of what is being generated while the board is active.

That's a good point, see if the +/- test points on this board show continuity with another point.

And still I'd like to see the board diagnostics with the Actel chip removed. If it shows additional failures with the Actel chip removed, we could assume that it isn't dead (or not fully dead)
If the failures stay the same then, well I guess we're still at 50/50.

[c4757p]

Working atop nitro2k01's great suggestion that some of the DAC's input pins are stuck high or low, I tried simulating this in MATLAB. Forcing certain bits on or off didn't quit produce the right output (in particular, the signal would show frequent excursion to fullscale high and low, which you don't see here). But, long story short, if you simulate that the DAC has failed in such a way that it just sums all the input bits and just outputs that sum (outputting b1 + b2 + b3... instead of 1 * b1 + 2 * b2 + 4 * b3...), you get a very familiar looking graph (attached).
...
As a side question, I'm wondering if this idea makes any sense: I'd go around and test the voltage across the op-amp inputs (input- vs input+). According to the whole virtual earth principle thing, they should be equal (unless the output is saturated). If you found just one or two op-amps that failed VEP, maybe it would be worth a shot at socketing+replacing those. This obviously requires you to be able to probe the live board, though.

If the DAC is something like an R-2R, you could get this effect if all of the low-side drivers were disabled. Check the negative rail to the DAC!

Edit - or the high side, of course, you'd just have the inverse... but we've already been checking negatives.

[Stonent]

Rather than wire up every single op amp, why not take the time to wire up an extender?

An idea I had thought of earlier in the other thread is some kind of low profile 8 Pin DIP test clamp that goes on the chip where you can take all the INs and OUTs and visualize them on one or more scopes.

[parabuzzle]

so how much did Dave pay for this thing? I know in the first video he said it would be an expensive paper weight if he couldn't fix it...

[TMM]

A board extender would be very nice to help for testing (the op amps).

A board extender is pretty much essential at this point.

If you do get/make board extender maybe you can use that AIM TTI Current probe that you reviewed to quickly find out what op-amps etc are buggered?
I assume you still have that probe.

The currents for the signal stuff would be way too small to pick up anything useful. It may find a short on the powersupply but imho an IR camera is even better for pinpointing those faults.

[cibola]

From my perspective, I'm learning so much more from the failures than if this had been just another easy fix.

I'm sure it's really frustrating for you, Dave, but it is certainly serving the purpose of producing a great series of videos on troubleshooting. It doesn't matter to me whether you get the damned thing fixed; it's learning about the troubleshooting process that's important to someone of my limited experience. And, a better understanding of the role of the components in the various circuits.

Keep on (at least for a while longer).

[rs20]

If the DAC is something like an R-2R, you could get this effect if all of the low-side drivers were disabled. Check the negative rail to the DAC!

Edit - or the high side, of course, you'd just have the inverse... but we've already been checking negatives.

Oh, you're absolutely spot on. If the DAC's not getting the right high or low side supply (who knows whether they choose to do the design "upside-down" from the schematics we're used to), then you could fully expect this behaviour.

[EEVblog]

Keep on (at least for a while longer).

I will, but likely won't do any more videos until I can beg/borrow/steal/make a DIN41612 extender card or cable.

[SeanB]

One card socket, one plug and 3 pieces of veroboard. Solder rows of socket edge on to veroboard and to the cut off edge of the plug. Then place another on top and repeat. Did that to make an extender for a avionics computer so I could reach the test points they conveniently placed just too far inside, and this one had the only set of sockets that were not common to the other cards. Good enough for occasional use.

[Ronald1962]

Hi Dave,
check your email...
Regards
Ronald

[mikemcginn@mcginnweb.net]

I think every op amp in that beast is dead. The question is - what else is dead? If it were me, I'd pull and replace every op-amp in the thing and see where I was. Fixing old stuff is my hobby. I can't speak for Dave.

Dave may feel differently. I have a Tek 453 I am working on. When it is fixed I have to find another old Tek to fix. Vicious cycle.

[kb3pxr]

The fact that your V/- 6.2 volts are reversed from the silkscreen is a red flag. Check the service manual to see if they have a note about the silkscreen being wrong (if the silkscreen is wrong it should have the note, especially if it isn't the first edition). Fix that first, then trace down the other bugs. Shotgunning the op amps would be a waste of time since if all or even most of the op amps are blown, their are going to be other ICs that aren't as easily obtained blown as well.

[codeboy2k]

Watching this repair series makes me re-think my strategy for power rails on my boards... If the HP engineers had only put a simple zener diode and a fuse (link or thermal) as overvoltage protection on the rails, perhaps it would have survived and fewer components (ultimately NO components) would have been damaged.

by the way, Sony has patented the use of a zener diode, a PTC resistor and a thermal fuse for overvoltage protection.
I didn't know that.

http://www.google.com/patents/US6700766

It's not clear to me if the patent only applies to battery packs, or if it applies whenever you use those 3 devices, or if it applies when the 3 devices are in close proximity so as to transfer thermal energy to each other thus decreasing the response time.  They claim all 3 (among about 20 other variations too).

A zener and a thermal fuse can help protect against over-voltage, but a sustained overvoltage can overheat the zener, so they put a PTC in series with the zener, and that limits the zener current. Then they patented it.

[SgtRock]

Dear Dave:

--I recommend you get a used Hakko 470 or something like. It is a treat! I prefer the 470 over the 808, because it is much easier to use, since you are not carrying the weight of the motor, and, being smaller it can get into more places. I even use it to re-solder with if I only have one or two easy ones to do. When you no longer have to dick around with a spring operated solder sucker and braid, and can remove devices at the rate of one second per pin, with no destruction, your use of bad language will drop considerably. Many parts just fall out with no persuasion. Even if you do not  use it on this particular project, I promise you, you will not be sorry!

"I see, Its a profit deal"
Steve Martin 1945 -

Best Regards
Clear Ether

[c4757p]

by the way, Sony has patented the use of a zener diode, a PTC resistor and a thermal fuse for overvoltage protection.
I didn't know that.

http://www.google.com/patents/US6700766

It's not clear to me if the patent only applies to battery packs, or if it applies whenever you use those 3 devices, or if it applies when the 3 devices are in close proximity so as to transfer thermal energy to each other thus decreasing the response time.  They claim all 3 (among about 20 other variations too).

A zener and a thermal fuse can help protect against over-voltage, but a sustained overvoltage can overheat the zener, so they put a PTC in series with the zener, and that limits the zener current. Then they patented it.

It's freaking pathetic that using three devices together for exactly their already existing intended applications can receive a patent.

[Low pass]

I scoured google looking for the circuit diagram but no joy here either.
sometimes when I want something I can't find online I get lucky by emailing
people at say HP who might have access to data i am after and who would be willing to
do the favor.  especially since this is somewhat outdated tech.  just an idea to kick around. 

[EEVblog]

--I recommend you get a used Hakko 470 or something like.

Quite rare to get one here in oz.
I've picked up a local cheapie, as new Hakko's in oz are very expensive, about to shoot a video on it right now...

[diehard67]

forgive me if this is an incredibly dumb idea but I thought that an 8 pin dip socket used in a rather unusual way could be used to test those op-amps with out removing them from the board.

just put the socket down on top of the op-amp using the sockets legs like probes and connect the test circuit whatever you choose to the top of the socket, not sure how well this would work but sense the power for the part would come from the test circuit presumably on a bread board then you could test em without having the board in the dsa housing.

probably a dumb idea but it sounded better then soldering wires to every signal pin on every part and running all them out the side to test and get em all mixed up lol

anyway good luck getting this thing to work

[notsob]

Test clips for DIL chips have been around forever, here's some samples

http://www.digikey.com/product-search/en/test-and-measurement/test-clips-ic/2294786

[trackman44]

Hi Dave. I have been following your blog for quite some time now. You were having a dilema about how to go about fixing the HP35670A and you were contemplating fixing it with some kind of extender card. Here in Toronto i found a couple of cards ( made by Sony, don't know what they are for) that have that 3 x 32 connector. I sent them in the mail for you to look at and hopefuly, you could use them to diagnose and test the A4 or A5 card on your DSA. I sent you a couple of e-mails in regards to this. Good luck with the repair. 

Will

[M0BSW]

And the next episode will be when !!!!!!!!!!!!!!!!!

[Stonent]

And the next episode will be when !!!!!!!!!!!!!!!!!

I know, right? I love to watch other people spend money.

[M0BSW]

And the next episode will be when !!!!!!!!!!!!!!!!!

I know, right? I love to watch other people spend money.

Ha ha ha , I just want to see him fix it, it used to work so it should work again, I'd find it a pride thing, perhaps that's why I'll never have my own business  .
I'm surprised the HP/Agilent or who ever owns the company haven't stepped in to help, I thought Dave had a strong bond with them.

[Kjelt]

I'm surprised the HP/Agilent or who ever owns the company haven't stepped in to help

Ten years ago: these companies in europe at least gave a huge discount on a new spectrum analyzer when the old one was swapped back.
They then destroyed the old equipment (at least what they told me).
So in fact they bought back their old spectrum analyzers for a huge amount of money just to keep these equipment off the second hand market so it would not cannibalize their new product portfolio for small companies.
It was a pain to see since in that time the company i worked for sold the old equipment for almost nothing to their own employees
So I think it is very tough to get any documentation, only hope is an old HP employee has his own document archive copy somewhere.

[M0BSW]

I'm surprised the HP/Agilent or who ever owns the company haven't stepped in to help

Ten years ago: these companies in europe at least gave a huge discount on a new spectrum analyzer when the old one was swapped back.
They then destroyed the old equipment (at least what they told me).
So in fact they bought back their old spectrum analyzers for a huge amount of money just to keep these equipment off the second hand market so it would not cannibalize their new product portfolio for small companies.
It was a pain to see since in that time the company i worked for sold the old equipment for almost nothing to their own employees
So I think it is very tough to get any documentation, only hope is an old HP employee has his own document archive copy somewhere.

Cricky is that what they used to do !!!!!!!! how strange, I have some old Black*Star equipment made quite locally to me not in the same league of course, Thurlby  Thander bought black*star out and  their sale team have been the most helpful people  when I needed a schematic  & user manual very impressive, so much so I would buy thurlby Thander known as TTL equipment in a heart beat now.

[Stonent]

I'm surprised the HP/Agilent or who ever owns the company haven't stepped in to help

Ten years ago: these companies in europe at least gave a huge discount on a new spectrum analyzer when the old one was swapped back.
They then destroyed the old equipment (at least what they told me).
So in fact they bought back their old spectrum analyzers for a huge amount of money just to keep these equipment off the second hand market so it would not cannibalize their new product portfolio for small companies.
It was a pain to see since in that time the company i worked for sold the old equipment for almost nothing to their own employees
So I think it is very tough to get any documentation, only hope is an old HP employee has his own document archive copy somewhere.

Cricky is that what they used to do !!!!!!!! how strange, I have some old Black*Star equipment made quite locally to me not in the same league of course, Thurlby  Thander bought black*star out and  their sale team have been the most helpful people  when I needed a schematic  & user manual very impressive, so much so I would buy thurlby Thander known as TTL equipment in a heart beat now.

When I tried to contact Kenwood about an old Trio-Kenwood scope I was told that division of the company didn't exist any more and was given a phone number and address of a company that serviced them with the caveat that they went out of business a few years ago.

 

[vaualbus]

Dave check back the agilent forum you made. Someone apparetly want to send you the acquisition schematics!

[Omcsesz]

Hi Dave,

I have the service manual. If you're interested, just send me an email, and I'll forward it.

[Rasz]

afair Dave said on twatter he has schematics now

[tridentsx]

Dave I believe you have the schematics and I saw the bus extender cards in previous mailbag
Please don't give up ,continue when you have time. I love these videos its like watching an
Agata Christie murder mystery. "Ten little op amps"

[vaualbus]

Day given the fact you have the schematics you could continue the series. You said that you we'll continue the series as soon as you have time, When we could have the next video we have to wait a lot of time?
Despite that, The first think I would do is to adjust the -18V rail to -18 and no like now ( from part 2 the -18V rail is to -19.2).
I still think that the dac and adc are good but the op amps (change  all the same op amp that you have arleady replaced) are bad.
Best luck and let us now when you'll continue the series. (You could do a live show repairing the instrument).
As you could understand I really like the repair video, I wish to have other videos on instruments reparing.
If you ever buy a TDS 540 tektronix scope and If you need the schematics, tell to me (I have the original no revision TDS540 schematics).
Best regards, Alberto.
Happy Christams and happy near year. 

[ilanko]

More progress (or is it?) on the HP35670A DSA repair.
Part 2:
Part 1:

When is HP35670A DSA Repair - Part 4 ?

[jlmoon]

I just watched the video,  noticing the mode of failure.. I have seen this many times in high speed audio stuff..   Main power supply failure > sub regulators and op-amps.. high probability of substrate puncture from Lightning or ESD damage..

JM