Black Jupiter 2000 Function generator circuit.

[johnmcgivern]

Hi lads, My function generator has a fault no amplitude output but the neon comes on looking for circuit to try and repair. Tried net but no good.
Best regards, John.

[Shaman]

Hi John please see if the link below is of use. You could contact the company for manual/circuit perhps...regards...Alan.

http://www.farnell.com/datasheets/105018.pdf

[Yorkie]

I notice from the datasheet that the service manual didn't come with the Jupiter but was listed as an optional extra, so might not be very commonplace, but hopefully one will turn up. Without a circuit, a few preliminary checks could at least be made - for example, the voltages/ground connections of the ICs. Given the era in which it was made, though the blurb refers to it using a 'microprocessor' I wonder if it used the then popular but long since obsolete 8038 waveform IC? If so, they do sometimes turn up on internet (eBay etc). Any electrolytics may by now have high ESRs but whether that would stop it working is debatable.

There is a schematic available FOC from this site, but you have to register to get it, but I know nothing about the site - 'ride at your own risk'!:

http://documentsearch.org/pdf/black-star...matic.html

Best of luck in your quest John.

[johnmcgivern]

Hi John please see if the link below is of use. You could contact the company for manual/circuit perhps...regards...Alan.

http://www.farnell.com/datasheets/105018.pdf

HI Alan, will email company for circuit. Dont know what to look for nothing looks burnt 18v on TF secondary.
Many thanks.

[johnmcgivern]

I notice from the datasheet that the service manual didn't come with the Jupiter but was listed as an optional extra, so might not be very commonplace, but hopefully one will turn up. Without a circuit, a few preliminary checks could at least be made - for example, the voltages/ground connections of the ICs. Given the era in which it was made, though the blurb refers to it using a 'microprocessor' I wonder if it used the then popular but long since obsolete 8038 waveform IC? If so, they do sometimes turn up on internet (eBay etc). Any electrolytics may by now have high ESRs but whether that would stop it working is debatable.

There is a schematic available FOC from this site, but you have to register to get it, but I know nothing about the site - 'ride at your own risk'!:

http://documentsearch.org/pdf/black-star...matic.html

Best of luck in your quest John.

Thanks for replying Yorkie there is no 8038 chip but these are the chips on board.
CA 3089 NPN transistor array.2 off.
DM74LS37N Quad 2 input nand buffers. 1off.
NE527 Voltage comparator. 1off.
071CDP Op amps. 4off.
072CDP Opamp 1off.
Variable resistor15 off ha ha.
I,ll have a go at checking voltages and gnds.
T/F centre tapped 18v either side 36 in all no markings on T/F to check specs.
I am just a novice I was using the generator to do rf alignment on a Pilot u650 1936 radio resoration nothing seemed to be happening so hooked up to scope and there was no amplitude on signal I had bought the scope on ebay hardly ever used it sods law I only bought it to try and learn how to use it not repair it ha ha.
I tried the site for schemeatic registered then they asked for money I hate it when they make out its free so never bothered. I started this Pilot restoration about 9mths ago was warned about the bug but I am afraid I got it can,t leave it alone now ha ha. Learning all the time wish I had started 50years ago.
Many thx, John.

[Skywave]

When you've got a piece of test kit like this and it isn't working the way you describe and the cct. diag. isn't available, the best chance you have of diagnosing the trouble is first to get the data sheets for all the int. ccts. that are used and wander around the cct. with a 'scope, paying particular attention to waveform shape and amplitude at the various int. cct. pins, using the datasheets as a guide. It's also a good idea to check that the supply voltages at the appropriate pins of the int. ccts. are present: in fact, this should be done first!

Al.

[Paula A]

Jump straight at the NE527 .. in my experience unreliable.

[Yorkie]

Being obsolete, I'm not sure that the NE527 is that easy to find. However, at this link you can get a pack of 20 for £3.86+£4.31 P&P, £8.17 total, from Bulgaria:

http://www.ebay.co.uk/itm/20x-NE527N-NE5...0479666844

True, you don't need 20, but you could always keep a few and sell the rest on eBay!

Best of luck with it John.

[Mark Hennessy]

Hi everyone, received circuit.
Checked voltages on IC's all good apart from IC3 AND IC4 should be +20v and =20V both are 3.5v higher +23.5 =23.5.

These supplies are unregulated, so I wouldn't worry too much about that...

Struggling with how circuit actually works any suggestions would be most grateful.

Despite the apparent complexity, taken at a "block diagram" level, it's actually pretty generic...

The way the triangle waves are made involves putting constant currents into a capacitor. First the capacitor is charged, and when it reaches a predetermined threshold, the polarity of the current is reversed, and the voltage heads down towards the negative threshold, at which point the current is once again flipped and the cycle repeats.

The comparator that determines when the positive and negative thresholds are reached outputs a square wave, which controls the current to the capacitor. This square wave is also available as an output.

To make a sine wave, the triangle wave is deliberately distorted, taking advantage of the exponential relationship of VBE and IC in a transistor.

Looking at the diagram, IC3 is the positive current source and IC4 is the negative. The op-amps before these control them, summing the frequency control and the external input. These currents are fed into a diode bridge, which is used to determine whether the positive or negative current reaches the timing capacitor.

You'll note that the frequency decade switches are able to change the capacitor being charged (C1 to 4), and also the value of the resistors in the current sources. By altering the currents, you need fewer capacitors (large ones get expensive, so reduce the charging current instead). IC5 is almost certainly being used as a capacitance multiplier instead of a 10u non-electrolytic device. You'll also note the duty-cycle control, that alters the balance between the currents...

The output from the capacitor goes to the FET (TR5). A high impedance is required here, as any current taken will distort the triangle wave. The following transistors in the CA3086 form a conventional amplifier, the output of which is on TP9. It goes to 3 places; the comparator (IC7), the sine converter (bottom right) and the waveform selector switch.

The comparator is a conventional enough circuit, with the output being amplified and buffered and fed back to the diode bridge (arrow A). The output from the chip is also fed to the TTL buffer and the wavechange switch.

The amplifier takes the "mixsig" from the switch and deals with it in a conventional manner, and has constant-impedance attenuators dealing with the output. Similarly, the PSU is entirely conventional, but perhaps not at glance if you're more familiar with 78xx regulators...

Incidentally, I built one of these some years back - probably with more transistors and discrete circuitry than this one, which is how I'm so familiar with it

I think there has been a new revision on this drawing as it calls for 2 off TL072.
There is only one on the board unless I am reading it wrong and there is a distinct possiblity that I am.

No, definitely two shown on the diagram...

Time to take some measurements to determine where the fault lies. Any sign of the TTL output? Any signal on the capacitors? Is there a DC output - a faulty comparator would probably stick at one rail, so you should have a voltage on the timing capacitor...

As you say the power supplies are OK, this might not be completely straightforward, but look for common-sense stuff first.

Good luck,

Mark

[Yorkie]

Just a point which has been lost in the discussion about what might be wrong with the generator John, you wrote:

I am just a novice I was using the generator to do rf alignment on a Pilot u650 1936 radio resoration nothing seemed to be happening so hooked up to scope and there was no amplitude on signal I had bought the scope on ebay hardly ever used it sods law I only bought it to try and learn how to use it not repair it ha ha.

Without wishing to sound patronising, that generator is for such tasks as checking the distortion of amplifiers - it isn't the right equipment to align RF stages of radios, and unless you connected it via a dummy load, it isn't the right method. Furthemore, you should never connect a generator or other test gear directly to a radio - only via a 0.1uF high voltage (EG, 630V DC) capacitor or you risk damaging the output circuitry of the test gear.

The U650 is quite a complex receiver, in that it has four wavebands and an RF stage. I'd be extremely reluctant to tamper with the RF alignment unless someone else had tampered with it first. It's highly unlikely that the alignment will be off tune. The service sheet for the U650 states that you should first align the IF stages (via a 0.1uF high voltage isolation cap, then the RF stages via a dummy load connected to the E & E sockets. It outlines thart the sequence should be MW, SW2, SW1 and LQW in that order, and it detials how this should be acomplished.

I'm wondering therefore, whether - if you connected the Jupiter directoly to the front end of the radio without an isolating cap - you may have damaged the output circuitry (TR20, & 21 for example?) Worth checking if you have a square wave as shown on the circuit of the triangle generator and waveform shaping circuit at S10, next to TR11. If you do, at least that narrows it down a bit.

I hope these comments sound helpful rather than critical John.

Best of luck!