Fluke 8840a Bench Multimeter

[xwarp]

If pressing makes the microprocessor work then you either have a broken socket or dirty pins, or a cracked joint on the main board. Clean and check, you will probably have to unsolder the socket on the mainboard if it is faulty, though I have bodged a new socket onto the old one before by cutting it off and soldering a new turned pin one onto the stubs, no way was I going to try to undo all the soldered wire wrap spaghetti under the original board, especially as it was about 10 layers thick there. peeled the plastic housing off and left the socket pins bare for easy access to solder.

Now it's working I think I'll leave it alone.  I couldn't see anything underneath the board that obviously looked wrong, and I don't have an IC extractor to pull the chips out so I can clean the pins and socket.  This piggy back arrangement seems a bit fragile.

Anthony

Of the 10 8840a's and a/af's that I have worked on, that's a first to see that eprom piggy backing the U202 chip. All of mine have that eprom in the socket labeled as U222, and, it appears that your main board has a chip in that socket also.

Wonder why?

[SeanB]

Either they ran out of the mask rom chips, and looking at remaining product life and the cost of having a minimum run of 100k parts fabbed from the original mask set ( minimum order and likely the fab would have a 6 month lead time to make the basic wafers as well so delivery would be in a year or more), they decided to simply do the last few thousands using a production item of the development kits microprocessors, as they were likely still available, and even if they were 20 times the price of the mask version they would work out cheaper than buying in the mask rom for under 10k units.

[DRT]

Judging by the date codes (at least a year earlier than my own non-piggyback model), I think this a very early unit rather than a 'last run' unit.

[SeanB]

Same reason then, the one year or so lead time for the mask product, and then they likely went through a few firmware revisions developing it before deciding to commit to a final mask layout.

[xwarp]

Did not dawn on me till a few minutes ago that it looks they were just stacking memory there.

[aroby]

Judging by the date codes (at least a year earlier than my own non-piggyback model), I think this a very early unit rather than a 'last run' unit.

On the back of the main board it says (c) 1983 and board Rev D.

Anthony

[Jf2014]

Hi Anthony

In the picture I can see that CPU's firmware is V 2.5
In my 8840 there is a damaged processor. ( Z6211 with ROM mask)

I have built CPU's adapter on U8840 with external EPROM.
Unfortunately, I have found only v2.3  firmware on the net, but it doesn't work correctly
I need a version 2.5.

Could  you make the dump of EPROM for CPU ( U202) ?

[xwarp]

If you want to message me your email adx, I'll send you the 2.5 bin file.  Not sure if it's allowed to be attached here.

[Jf2014]

If you want to message me your email adx, I'll send you the 2.5 bin file.  Not sure if it's allowed to be attached here.

Thanks for the file, but unfortunately it is not a file for CPU U202
I need a version 2.5 for U202 ( not U222 )

[motocoder]

In case anyone is interested, the attached photo shows how the two meters turned out after minor repairs, cleaning up the stickers, and repainting the main chassis cover.

[xwarp]

If you want to message me your email adx, I'll send you the 2.5 bin file.  Not sure if it's allowed to be attached here.

Thanks for the file, but unfortunately it is not a file for CPU U202
I need a version 2.5 for U202 ( not U222 )

My bad, I thought you needed the bin from 222.

Let me see if I can rip it from u202. Not sure if I can with the G540 programmer.

[aroby]

In case anyone is interested, the attached photo shows how the two meters turned out after minor repairs, cleaning up the stickers, and repainting the main chassis cover.

Nice.  Mine is a muddy green color.  I guess it was ex-Army.

[aroby]

Hi Anthony

In the picture I can see that CPU's firmware is V 2.5
In my 8840 there is a damaged processor. ( Z6211 with ROM mask)

I have built CPU's adapter on U8840 with external EPROM.
Unfortunately, I have found only v2.3  firmware on the net, but it doesn't work correctly
I need a version 2.5.

Could  you make the dump of EPROM for CPU ( U202) ?

Sorry, I only just saw this.  I don't have anything with which to dump the EPROM.  Not sure that I want to pull this out of my unit - it looks like it would be a nightmare to get it plugged back in.  If you have any suggestions how to do the dump without pulling the EPROM out, let me know and I'll have a go.

Anthony

[salbayeng]

Hi Guys,
Not sure if anyone is still watching this thread,
But I had a similar intermittent problem, due to a dry joint inside the piggy back socket.
I've fixed it and posted it here: https://www.eevblog.com/forum/testgear/fluke-8840a-intermittent-relay-clicking-resetting/
Thanks to everyone for pointing me in the right direction!

[bson]

The larger IC is the Z8 CPU.  The EPROM (not EEPROM) on top is the program ROM.

Wow, they used a Piggyback Z8??? I built a few boards with it in the 80s and it was the neatest thing ever.  Never saw it in any other products though.