hp4194A problem

I work as a tech for a company that salvages and repairs test equipment.

We don't normally do repairs for third parties, though...

I haven't worked on this particular piece of equipment (yet) but start with the service manual:

If that link doesn't work go here and navigate to the manuals section:

This would be a tough one, as the schematic of the A6 and A7 boards is unreadable (Why did they even bother?) There appears to be two banks of DRAM on each board, each bank is 256KB. Given this, it appears that the upper bank of memory is defective on either the A6 or A7 board. Start by probing the WE, RAS and CAS lines on each bank of A6 and A7. If they appear OK, look at each DRAM's data line for a bit that may appear to be tied or faulty. If you had a signature analyzer, that would be a plus!

[Sorry for the repost, but I just noticed that sci.electronics.repair is not in the groupline - I've taken the liberty of adding it.]

I work as a tech for a company that salvages and repairs test equipment:

We don't normally do repairs for third parties, though...

I haven't worked on this particular piece of equipment (yet) but start with the service manual:

If that link doesn't work go here and navigate to the manuals section:

This would be a tough one, as the schematic of the A6 and A7 boards is unreadable (Why did they even bother?) There appears to be two banks of DRAM on each board, each bank is 256KB. Given this, it appears that the upper bank of memory is defective on either the A6 or A7 board. Start by probing the WE, RAS and CAS lines on each bank of A6 and A7. If they appear OK, look at each DRAM's data line for a bit that may appear to be tied or faulty. If you had a signature analyzer, that would be a plus!

sounds like a bad memory chip or the chip has been removed! :)

--
"I'm never wrong, once i thought i was, but was mistaken"
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5

Download the manual and troublesoot the thing:

--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

Yeah, but take a close look at the schematics! They're practically useless.

hi, Thanks for your earlier replies. i tried to solve theis problem. Before taking any step further, first what i did was just shook the instrument gently and opened it. I took out the A6 and A7 boards and inserted them back in again.upon turning on the power supply now the error message has changed to "B: ROM check sum err 004". Please suggest how to get it fixed. thanks. kristo

[restored non-quoted text]

This error is indicating that the problem is now in the A8 board's ROM located at U4. Is the problem consistent over multiple power ups - do you get the *exact* same message each time you cycle the power? If so, you could try re-seating that board as well checking the gold fingers for contamination/dirt. If that doesn't solve the problem, I would begin by getting the pinout for U4 and probing it's chip select and output enable pins. Also, have you checked the voltages on all the power supply outputs as well as checking them for ripple?

Unfortunately, the schematic of this board is just as bad as the A6 and A7 boards.

Thanks. Yes the problem is consistent now, all the time showing same message. I have not tested the power supplies..i am going to do the things you have suggested..thanks.