HP 54501A troubleshooting - repair

[ddavidebor]

hi guys!

i've bought 2 HP 54501A. old very-high-end scopes. 100Mhz but only 10Msa/s
one don't power on... and the other one says various error...

i'm going to post here about this repair.

scope that work bad:
various error, including a/d, memory and DAC error. smell like corrupted calibration data.
it's fault of the NVRAM (non volatile ram)... it has 2 litium battery... but not user or service serviceable...
so, i've found a compatible replacement DS1230Y-120+ from maxim. i've ordered 2 (maybe non-original) from china to be sure, but i'm going to use original and expensive ones from dallas semiconductor.
i've already removed the chip... it's very difficult, for be sure to don't damage the board i've destroy the chip...
inside is all trough hole tecnology... zero smd 

i've also clean the main board and the power supply.
next things to do
-replace the nvram
-clean all the case
-check the fan
-clean the HV CRT board 
-disassembly the front panel and clean the soft button
-reassembly all
-calibrate it
-complete function check

for the scope that doesn't work at all:
there wasn't fuses. i've inser good fuse in it, powered on and.... smell burned electronic   
but for 6-7 second it boot correctly and displayed same error of the other one scope...
so i've open it... disassembled the power supply board and... old electrolitic caps fluid everywhere!!!

so i've desoldered all this NO BRAND CHEAP CAPS (the power supply was OEM from a hong kong company...)
i've also clean the board in isopropilic alcool for 4 hour... now is clean...
i will buy new caps soon...

things to do:
-buy new caps
-solder new caps
-check the power supply voltage
-destroy and desolder the nvram
-replace the nvram
-clean all the case
-check the fan
-clean the HV CRT board 
-disassembly the front panel and clean the soft button
-reassembly all
-calibrate it
-complete function check

--------
soooooooo
little funny "old-stile" things..

all though hole
the fan is "made in we-germany"!!!!!! i think dave will love this... it's before the fall of the berlin wall! great piece of history
the oscillator are from FOX

[Hydrawerk]

How expensive were those two scopes?

[ddavidebor]

150€ for two

[Wuerstchenhund]

Just a word of advice, before you go through all the work of cleaning and such you should replace the mains filter. It's made by Schaffner and at this age tends to blow up, leaving a sticky, aggressive black gunk spread around the innards of your scope. The filters are standard products (as are the power supplies in these scopes btw which were made by Computer Products/Artesyn) and are still manufactured, just be sure not to buy "old stock" as due to age the old stock is unlikely to be better than your current filter. Old ones were manufactured in Switzerland while newer ones were made in Thailand so if the filter says 'Made in Thailand' it should be ok.

The Dallas NVRAM block can be replaced by a SRAM chip which doesn't require a battery to hold its data, and since the scope doesn't have a clock the lack of battery is no problem.

The 54500 Series are very good scopes, and very durable (more so than the 54600 Series which was built for low costs). It takes a bit of time to get used to the single rotary dial + menu system interface, though.

[rf-loop]

The Dallas NVRAM block can be replaced by a SRAM chip which doesn't require a battery to hold its data, and since the scope doesn't have a clock the lack of battery is no problem.

Time ago I have repaired many of these and also changed NVRAM (with modification--> NVRAM socket (DS1213C but now obsolete) and normal low stand by current cmos ram. In this solution there can also measure lithium battery voltage. CmosRAM + DS1210 control chip is one solution.)
Also I have still many of these (just garbage units for spare parts if some day useful...  but example all PSU's salvaged time ago)

There is no clock. This is not reason.
There is calibration data and it need it! Without cal data old 54501A (and all 5450xA may be so much out of order that can not use. Worst case if data is "scrambled" there may be difficult to startup (I have some this experience also))
If cal data is lost. First do factory default and after then run full selfcal and it produce all needed data itself.

Of course with normal cmos ram it is possible to use if it starts and then do default cal data and then run selfcal procedure what takes so long time that this is not very practical,
 
Short time ago there was also  still available compatible NVRAM but I have not checked today situation.

[Wuerstchenhund]

There is calibration data and it need it! Without cal data old 54501A (and all 5450xA may be so much out of order that can not use. Worst case if data is "scrambled" there may be difficult to startup (I have some this experience also))
If cal data is lost. First do factory default and after then run full selfcal and it produce all needed data itself.

Of course with normal cmos ram it is possible to use if it starts and then do default cal data and then run selfcal procedure what takes so long time that this is not very practical,

I know that there is no clock (as stated in my previous posting already). But the thing is that these Dallas NVRAM blocks are getting harder to come by (and they are not cheap), so using SRAM (which keeps its content even when power is off) has proven to be a useful and cheaper alternative to replacing the Dallas block or hacking the old one.

And the other advantage is that by using SRAM there is no battery to replace, ever.
 
I can't remember the exact type of the SRAM chip I have used for various 54500 scopes but I should still have a spare one and I can look it up if necessary.

However, these Dallas chips are only used in the first generation of 54500 scopes (54501A, 54502A, 54503A, 54504A, 54510A) anyways. Later models (later production 54510A, 54510B, 54520A/C, 54522A/C, 54540A/C, 54542A/C) use a separate soldered-in coin cell battery which makes things much easier.

[ddavidebor]

thaks for the suggestion.

i will change the filter.

i prefer to change the nvram with another similar nvram to be sure that all work fine...

if the china-made nvram don't work or don't arrive and i can't have some samples, for sure i will do as you say: ds1210+cmosRAM, thanks!

thanks, i know the procedure after nvram fail

@Wuerstchenhund i'd like to know more about the sram chip you've used, thanks.

[MetraCollector]

You can read my story:
https://www.eevblog.com/forum/reviews/hp-54502a-nearly-vintage-digitizing-scope/

DS1230Y- substituent from China works well.
You can calibrate the machine at home, in my case I have only adjusted offsets and the rest of calibration process is automatic, you only need two T-BNC elements and three BNC-BNC cables with equal lengths.

Story will continue when I received probes for it.

[ddavidebor]

I know thanks...

I'm going to ordering the probes tomorrow...

[dimlow]

Just a word of advice, before you go through all the work of cleaning and such you should replace the mains filter. It's made by Schaffner and at this age tends to blow up, leaving a sticky, aggressive black gunk spread around the innards of your scope. The filters are standard products (as are the power supplies in these scopes btw which were made by Computer Products/Artesyn) and are still manufactured, just be sure not to buy "old stock" as due to age the old stock is unlikely to be better than your current filter. Old ones were manufactured in Switzerland while newer ones were made in Thailand so if the filter says 'Made in Thailand' it should be ok.

The Dallas NVRAM block can be replaced by a SRAM chip which doesn't require a battery to hold its data, and since the scope doesn't have a clock the lack of battery is no problem.

The 54500 Series are very good scopes, and very durable (more so than the 54600 Series which was built for low costs). It takes a bit of time to get used to the single rotary dial + menu system interface, though.

WTF I just put a new filter in the Solartron 7150 multimeter, now is this telling me there is one of these pesky mains filters in my54502A ?

I found the DS1253Y-120 was easy to get when i replaced it. Calibration was a pain at first before i realized i need to wait until the scope had warmed up before it would pass calibration.

[nctnico]

There is calibration data and it need it! Without cal data old 54501A (and all 5450xA may be so much out of order that can not use. Worst case if data is "scrambled" there may be difficult to startup (I have some this experience also))
If cal data is lost. First do factory default and after then run full selfcal and it produce all needed data itself.

Of course with normal cmos ram it is possible to use if it starts and then do default cal data and then run selfcal procedure what takes so long time that this is not very practical,

I know that there is no clock (as stated in my previous posting already). But the thing is that these Dallas NVRAM blocks are getting harder to come by (and they are not cheap), so using SRAM (which keeps its content even when power is off) has proven to be a useful and cheaper alternative to replacing the Dallas block or hacking the old one.

And the other advantage is that by using SRAM there is no battery to replace, ever.

You mean Ramtron's FRAM which is not SRAM ?

Anyway, some people use a Dremel to grind away the epoxy compound and replace the batteries in the Dallas modules.
Here is a whole page with such hacks:
http://www.betaarchive.com/forum/viewtopic.php?t=22000

[rf-loop]

... in my54502A ?

I found the DS1253Y-120 was easy to get when i replaced it. Calibration was a pain at first before i realized i need to wait until the scope had warmed up before it would pass calibration.

Yes, specially model 54502A. It is very sensitive for this. Also if some internal adjustment have drifted it may need readjust before cal pass.

These are not any kind of pain IF follow exactly manufacturer manual. There is exact instructions  how to calibrate and how long it need warm up before cal etc.  Why these need find using try and fail iteration method?   Professionals who are familiar with these devices accurately, they have written these exact maintenance and calibration instructions.

*  But 54501A is not at all so sensitive than this old 400MHz 54502A with 400MSa/s.

If there is difficulties in calibration there may need fine-tune some internal adjustments if they have drifted out (not very typical - exept if someone has made the adjustment without enough or any knowledge how to do it).

And no need "dremel". 
(btw, original version (extended reliability)  what HP used  have also 2 separate redundant Li cell and they are molded bottom of chip. But functionally it need of course only one. )

http://www.maximintegrated.com/datasheet/index.mvp/id/2648

If chip have been just only in stock this is not problem even if some years.
Li cell backup is activated  after this chip see first time power.

[Wuerstchenhund]

You mean Ramtron's FRAM which is not SRAM ?

No, I mean SRAM, not FRAM. I checked the IC, it's a STK16C88 (256k nvSRAM). Years ago I've used quite a few of these to replace the Dallas blocks in older 54500 scopes. Albeit most of these scopes have probably passed the zenith of their lifetime, I found it more sensible to replace it with something which doesn't have a battery inside.

[nctnico]

But how is it going to retain its information? I guess HP didn't put the NVRAMs in there just for fun.

I agree that these scopes are probably a waste of time and money. I sold my DSO from the eighties a couple of years ago while it was still working.

[SeanB]

It is a SRAM with a shadow eeprom that copies the data into it at power down ( small cap provides power to do the write) to store it.

[nctnico]

So its not an SRAM but actually another type of NVRAM.

[ddavidebor]

here the pre-wall-fall fan

today i've disassembled, totally clean and reassembled all.

the quality of this scope is absolutely amazing! i've never seen in my life anything like this. all gold plated, all perfect after 20 year.

in fact, is a old scopes but
-you get a 100Mhz scope with 4 channel for repetitive signal
-it's a fantastic piece of equipment
-it's incredibly well-made, and super quality
-you can trust this scope!

i like it... i've two, so i will sell one, but i don't know if i can sell the other

[ddavidebor]

some other pictures after the cleaning

the cathode ray tube cleaned, the wire clean, the board clean, the case clean, the HV board clean, the keypad cleaned (all the 3 board), the various bnc disoxidated and cleaned, cleaned also under the input shield... the fan is also clean now... the screen clean...

in conclusion, all clean!

it take me about 6 hour. a lot of sticker on it, removed for grace of professional grade product.   %-B

i need some other caps because i've take 220u instead of 2200u

[ddavidebor]

The substitution main filter has arrived for the two scopes.

Now i'm attending the new nvram....

Ones is pretty ok, i will test it for 5 hours and i hope that it will not go on fire... Next i'm going to calibrate it completely (not only self cal).

The other one... Mmh... The power supply is still not in the best condition.

I've changes the varius caps, and a mosfet.
. But i think probably there will be something other damages.

And because mom hp has not released the full service manual, i must keep the working power supply in order to repair the broke one...

[Greg981]

Hi folks,

I've just been given a 54503A oscilloscope, and although it appears to be working, there is a problem that I'd like to address.  The NVRAM has just been replaced, like for like with a new part, and I've powered up with a front panel button pressed to load default values, and then been through the self cal routines (connecting rear panel BNCs to input channels).  The only problem I have is that the self test reports "FAILED  System ROM".  Running that test on its own gives "FAILED  System ROM Test 0000 0000 0000 0010, Failed Loops:8"
Anyone have any thoughts on this, please?

[Smith]

Has the device warmed up properly? I had strange problems with selftest when the device wasn't warmed up probperly (about 30 minutes).
Did you see this error before replacing the NVRAM? If not, you might want to reseat all EPROM's and connectors, and check your soldering work from the NVRAM. Maybe you've spilled some solder anywhere?

[Greg981]

I let it warm up for 3 hours today and then got the same.  The fault was present before replacing the NVRAM - which I did more in hope than expectation.  Soldering is all good, and defluxed so I could take a proper look.

[SaabFAN]

I think it is possible you're dealing with a bad ROM that needs reflashing. These scopes are well beyond the guaranteed data-retaining time of their PROMs.
I just did this with my PM3320A: Pull all EPROMS, put them in my TL866CS Programmer and reprogram them after reading their contents.

In your case, you probably need to search for a set of ROM-Dumps for your unit. Or you're lucky and there's just a simple reseat necessary (in which case I would still refresh them as soon as possible).

Btw. has there ever been a device that contained the necessary programming-circuits to reprogram/refresh EPROMs before Flash-Memory conquered everything?

[Greg981]

Thanks, SaabFAN, that makes sense.  I knew that EPROMS don't have an infinite data retention life, and who knows what effect having a CRT near them has.  I'll try making copies of all four first, and see if the data I can recover from them is good enough.  I guess I'll have to use OTP rather than UV erasable types, but that should be fine.  Will report back when I have news.

[Greg981]

An update on my problem.  Replacing all four EPROMs with a set I managed to buy from another scope has cured my problem.