HP-5334a Universal Counter repair help, timebase generator IC ?

[RichardM]

Hi All

I purchased a non working HP-5334A and established I am not generating the TTL clock signal needed for all the 3 microprocessors etc. All power rails look good although one capacity looks a little suspicious. The clock signal is 4MHz and uses an IC I know nothing about, an ICM7209 generator IC. The clock signal circuit is as attached and looks pretty simply to isolate there is a problem ?. +5V is is on pins 3 & 4, I have tried anew crystal and replaced C35 & C99. I see 0.4V on Pin 1 & nothing on Pin 2 and 5.

I guess the ICM7209 has failed ? Should I will try pulling it out and setting it up on a breadboard ?

If it is dead what are my options to replace this IC ? Could I build another small circuit & circuitboard that generates the 4MHz TTL clock signal ?

As a hobbyist, any help/comments or suggestions always welcomed

Regards

Richard

P.S Could I use a signal generator to inject the clock signal externally if I remove much of the circuitry to at least test the device ?

[pqass]

If there's no activity on pin 5 of U18, I'd cut the trace and air-wire a can oscillator in its place.

https://www.digikey.ca/en/products/filter/oscillators/172?s=N4IgjCBcoGwJxVAYygMwIYBsDOBTANCAPZQDaIALGGABxwDsIAuoQA4AuUIAyuwE4BLAHYBzEAF9CAJnoxEIFJAw4CxMiCkU4YehBYgOXXoNETpYAKwAGeYuV5CJSOQoACALIAJAF7M2nSBAAVSEBdgB5VHdcdGwAVz5cCUkQOWgQAQATLgBaMCsIfy4QQnYAT1YkwNiUcXEgA

[RichardM]

OK, thanks. I may leave the trace alone. I will remove the IC and replace with a socket and just wire the 4 MHz oscillator into that for now.

I have also programmed an arduino nano to output the clock so may even try that while I wait for the oscillator.

Richard

[RichardM]

Just on the off chance someone else faces a similar issue with an HP-5334 I thought I would post an update here.

I definitely had no 4MHz clock and ICM7209 (U18) appeared dead. I have ordered a replacement.

In the meantime I programmed an Arduino nano to output 4MHz and used some breadboard leads to plug +5V, GND, and Pin3 (4MHz OUT) into the socket I put in place of the faulty IC.

On boot the device passes all tests and the ovenised oscillator is working fine

Now to clean the unit up and perhaps order some new power supply capacitors.

Does anyone know anything about replacing the battery in these units ? It appears strong (measures 4V). Do you lose critical calibration data if you lose battery power when replacing ?

Regards

Richard

[RichardM]

And the Arduino code in case anytone is interested.

void setup() {
  // put your setup code here, to run once:
pinMode(3,OUTPUT);
CLKPR = (1 << CLKPCE) + (B0001);
TCCR2A = ((1 << WGM21)|(1<<COM2B0));
TCCR2B=(1<<CS20); //PRESCALER=1
TIMSK2=0;
OCR2B=1;
OCR2A=1;
}

void loop() {
  // put your main code here, to run repeatedly:

}

[pqass]

Just on the off chance someone else faces a similar issue with an HP-5334 I thought I would post an update here.

I definitely had no 4MHz clock and ICM7209 (U18) appeared dead. I have ordered a replacement.

In the meantime I programmed an Arduino nano to output 4MHz and used some breadboard leads to plug +5V, GND, and Pin3 (4MHz OUT) into the socket I put in place of the faulty IC.

On boot the device passes all tests and the ovenised oscillator is working fine

Now to clean the unit up and perhaps order some new power supply capacitors.

Does anyone know anything about replacing the battery in these units ? It appears strong (measures 4V). Do you lose critical calibration data if you lose battery power when replacing ?

Regards

Richard

Glad to hear it was only the oscillator chip that was broken.

See this for more info:  https://www.eevblog.com/forum/testgear/keep-an-eye-on-your-hp-5334a-battery/
You probably should replace the battery before it leaks.  If you can't find one in the original format (likely) maybe a 3-cell AAA holder for NiMH batteries will do.

According to [first paragraph of] this: https://usermanual.wiki/Document/A5334B.283369013.pdf
"The HP 5334A is available for customers who also require a front panel setup memory..."
The B model doesn't have a battery nor Recall/Store buttons.  So probably no calibration data and as per the eevblog link, only results in an error if dead.

[RichardM]

Thanks for the links

It’s still unclear to me whether I can just pull the battery out and replace it with no backup power required ? Will I lose any calibration data ?

Richard

[wn1fju]

Turn the unit off, replace the battery, turn the unit on.  It is as simple as that.  The calibration is all done via potentiometer and trimmer capacitor adjustments and there are no stored calibration constants to lose.  The only thing you will lose is any stored front-panel settings if you have saved them previously.

[RichardM]

Thanks very much. I thought that may be the case but nice to have confirmation. Cheers.

[pqass]

Thanks for the links

It’s still unclear to me whether I can just pull the battery out and replace it with no backup power required ? Will I lose any calibration data ?

Richard

Yeah, sorry, I can't assure you that it's not holding any data other than front panel setup and GPIB address.

If you want to be sure, do what I did when I replaced my 3478A battery.  That is,
a. prepared a temporary 3.6V battery with diode and 330 ohm resistor in series with the positive terminal,
b. with the 5334A COMPLETELY DISCONNECTED FROM MAINS on an INSULATED SURFACE, solder the temporary battery in parallel to traces nearby the on-board battery to be replaced,
c. remove the old on-board battery and replace with a suitable replacement battery,
d. remove the temporary battery.

The reason to completely isolate the 5334A from mains or a metal surface is because your soldering iron tip will likely be grounded and so touching the B+ terminal will short the battery and thus the CMOS content will go poof!

I haven't been able to locate a service manual for the 5334A.  I've only found one for the 5334B. And according to that schematic, the chassis ground is connected to DC ground on the secondary side of the transformer.  So either you use an isolated (battery-powered) soldering iron with the 5334A powered on for the duration of the battery replacement or you do the opposite; the procedure outlined above.