AGILENT 34401A

[EE-digger]

I had a VERY similar problem on a 33120A function generator.  I have no idea if the two have any similarity but your symptoms give me deja-vu.

On the 33120A, a small reset chip was not coming up to full logic high output.  It was stuck midway up, hence resets were not clean for both the main and display processors.

I don't know if the 34401A actually has a separate display processor or not.

[wictor]

There is separate processor in front panel. It's getting all display data from main board cpu. If there is no data arriving to front panel, there is nothing displayed.

[coromonadalix]

the best course would be to have another display to do some tests,  or a logic sniffer  ...... to be sure

I wont argue with all voltages, but do a recheck, theres many of them

Its an old meter,  in mine i have done the recapping  to be sure, they where all working before, but the tantalums where ginving me frills, in one they where slightly brown"ish"

[SpencerTC]

Have you tried to get any response through GPIB (or other external communications)?

[coromonadalix]

With no screen   how can we know the gpib adress ?  unless you see it briefly

[HighVoltage]

With no screen   how can we know the gpib adress ?  unless you see it briefly

You just try them all, there are not too many possibilities.

[picburner]

With NI MAX you can do an automatic scan and it tells you which instruments are connected and their address.
I think you can do the same with Agilent's software.

[HighVoltage]

Yes, the Keysight software scans automatically for what is hooked up to any of the GPIB ports.

[lionelkjh]

Good evening; I made no attempt with the GPIB (because I do not have this big connector, nor software, nor interface!): in summary; I'm a little lost! I specify that this version and 2008 it is more recent than the first models released in the 90s. How to

[SpencerTC]

Well, the first thing I generally check with nonfunctional equipment is the easiest things...external communication (GPIB, serial), ensuring voltages are correct (that 3.3VDC test point is close to 3.3V, same with any other voltages noted on silkscreen/in service manual), unseat and reseat any socketed IC's, see if there are any unpopulated {or populated} footprints that could be looked at (ex. JTAG, serial), sniff around with logic analyzer.

I own a 34401A, although I've never had an issue with it and have not had a reason to become familar with the troubleshooting process of it. If  you happen to have a second instrument that you can compare voltages, signals, and responses to, then it can make the whole process much easier/quicker.

Try what you can and let us know what you find and I'm sure some more people will try to help (either I or some of the much more knowledgeable people on this site)

Good luck!

[coromonadalix]

just had a small problem with my second  34401  the white display connector would not "get up"  or stuck at "pressed position" not closing on the flex cable center pins  when i pushed it to do a verification 

Worth to check



@Lionelkjh  you can surely build the project  ar488 usb to gpib adapter for almost nothing, you can communicate thru serial console,   or even try with the rs232 if there is somthing going out of the meter
https://www.eevblog.com/forum/projects/ar488-arduino-based-gpib-adapter/



But for the rs232 normally you set the communication type with the meter menu .....  the talkback (you only read / see the meter readings / no interaction is possible, is done at adress 37 if i recall

[Keith956]

I'm having the same problem with a 34401A I picked up today. The reset line (pin5 of U553) is oscillating at about 4.5KHz, see pic. Disconnecting pin5 from the XPONRST line shows that signal still oscillating (and pin5 is at 0v) so it looks like U500 is perhaps driving the signal low every 225uS?

Someone mentioned this could be the SRAM failing self-test, is this SRAM still available? Any way to confirm this is the fault? Thx.

[artag]

U500 is an 80c196 and has a bidirectional reset pin. So yes, it could well reset itself as a result of a test failure and assert reset outwards.

The SRAM is a common 8kx8 cmos ram and is easy to find. However, it's supposed to be able to test the sram itself:  the very short time it takes to reset suggests it's crashing rather than failing a self test. I'd expect it to use internal memory to start with. It may only use the external sram for more complex functions. So I'd be more suspicious that the eprom is faulty (or the data bus getting corrupted).

If you have a wide logic analyser you could record address and data bus for the short period it runs for - that may show up a lost bit.

The continuous reset can actually be used to help you find the fault. Trigger your scope on reset and then probe the address and data bus with another channel. You're looking for all 0s, all 1s, a deformed waveform, or something similar that prevents eprom or sram data reaching the processor.

[Keith956]

Good idea about the logic analyser - I've got a siglent 2104X+ with the logic probes - would that work?

[artag]

Good idea about the logic analyser - I've got a siglent 2104X+ with the logic probes - would that work?

It's not enough to do a full bus capture, but it can do something useful. To be honest I'd start with the scope probe - it's far quicker and will show up something like a broken track fairly quickly. It's a multiplexed bus so you'll have to follow through address going out while ALE is active, that address appearing on the eprom, and then data getting back from the eprom to the cpu.

If that fails to find the problem, you'll at least have a good understanding of what the address is doing (you should be able to ignore the higher address bits if you're sure the eprom is getting its chip select) and you can dig in a bit further and try to understand why its crashing or resetting after such a short time.

You do need to be able to read the data and address off the scope's LA inputs. Most scopes will have a list mode that lest you do this but I don't know the Siglent.

[Keith956]

Just to mention - I managed to get a Cypress CY62256L-70SC sram from ebay (well actually 10 of them for $5.76). After replacing the chip the 34401A works fine, and passes the shift+power on self test.

[coromonadalix]

 

[HighVoltage]

Just to mention - I managed to get a Cypress CY62256L-70SC sram from ebay (well actually 10 of them for $5.76). After replacing the chip the 34401A works fine, and passes the shift+power on self test.

Nice, congratulations !
I have had great success with a few 34401A to bring them back alive with such repair.

What I have not found out was the reason for this sram to die.
Maybe the lifespan of these chips was reached.