HP 54501A Restoration and Calibration

[xrunner]

I should be receiving an HP 54501A oscilloscope this week for repair / restoration. I've wanted one for a while because we had them in my lab circa 1990's. I know there are other threads on it but I'm going to post a lot more pics of the insides / parts for other people that may benefit from them, as well as do some repairs such as replacing and socketing the NVRAM IC. I was also informed that one of the rear BNC jacks has been "dented" and so I'll be looking at how that can be fixed. I know it is a panel jack that goes to a push-on RF connector but I don't yet know what kind to order if I choose to make that complete new jumper assembly.

I also want to go through the full calibration including adjustments on the main board, but I do not have the "extender" that the manual says to use, so I'll be looking at how that might be done without it (the extender just moves the PSU out of the way).


Plus - I like GREEN !!! 

The actual scope coming is attached below.

[xrunner]

So it arrived this afternoon. Seems to work OK for the most part. It will complete all the self-test & self-cal routines but it will not store them, but I was aware of that problem and the part is on-order.

It also has a busted BNC jack on the back, I will be looking into a fix for that. Also found an original document in the case bag, looks like it was purchased by North Carolina State University.

[Wuerstchenhund]

Nice scope! We had them at work when they were new and I also had a 54510A as my own scope, and I love the single knob interface.

BTW, I'd strongly recommend to replace the Schaffner mains filter if that hasn't been done in the last 10 years as they tend to blow up and spread some corrosive gunk all over the mainboard. They are still made, usually not very expensive, and the new versions should be more reliable. Just make sure you don't buy "new - old stock" as that wouldn't really solve your problem.

[xrunner]

BTW, I'd strongly recommend to replace the Schaffner mains filter if that hasn't been done in the last 10 years as they tend to blow up and spread some corrosive gunk all over the mainboard. They are still made, usually not very expensive, and the new versions should be more reliable. Just make sure you don't buy "new - old stock" as that wouldn't really solve your problem.

Yea thanks - I've heard about that and I'm going to attempt to find a replacement that fits in the existing cut-out.

Here's a few more screen shots for today. I'm just posting these for anyone browsing the web looking for info that may need to see them.

So, I know that the NVRAM is bad (really the battery inside), so what happens when you run the self-test? On the back of the unit is a red switch that sets the calibration to either protected or unprotected. If that switch is in the unprotected mode, you see that it passes all the self tests (with a bad NVRAM). If it is in the protected setting, the self-tests do not pass the NVRAM, D/A converter, or A/D converter (with a bad NVRAM). And finally, you can see the screen at the completion of the self-calibration. However, once you turn it off it will all be lost with a bad NVRAM; but it does complete properly. 

Only other thing I've done is to pull out the power supply to see if it can be jury-rigged in such a manner as to allow one to tweak the tweakable adjustments underneath it without using the "extender cable" the manual talks about - I think it will be possible.

More to follow ... 

[Smith]

Better check the caps in the power supply too, they tend to leak. Maybe its better to replace them, before they go leak (and they will). Its verry common with HP scopes of that era. Mine had the same problem.

The mains filter is quite expensive, in europe at least. I did replace it, but it cost like 60 euro's. You could probavly find them cheaper on ebay.

Only thing I have to do on my 54502A is replace the fan, it's so loud! I already have a new EMB PAPST laying around.

[Wuerstchenhund]

So, I know that the NVRAM is bad (really the battery inside)

As to the bad NVRAM, I'd replace it with a FRAM IC instead another NVRAM module. Works the same and doesn't need a battery.

The mains filter is quite expensive, in europe at least. I did replace it, but it cost like 60 euro's. You could probavly find them cheaper on ebay.

I paid around £20 (around 25EUR) for a brand new one a couple of years ago.

[TAMHAN]

Redo the PSU _ASAP_. The Boeschert Cartridge WILL go "puber!" on you in the worst of times - happened with my 53310A MDO.

[rf-loop]

So, I know that the NVRAM is bad (really the battery inside)

As to the bad NVRAM, I'd replace it with a FRAM IC instead another NVRAM module. Works the same and doesn't need a battery.

The mains filter is quite expensive, in europe at least. I did replace it, but it cost like 60 euro's. You could probavly find them cheaper on ebay.

I paid around £20 (around 25EUR) for a brand new one a couple of years ago.

Do you know HP54xxx   memory handling /CE signal pass for using FRAM

FM16W08:

Users who are modifying existing designs to use FRAM
should examine the memory controller for
timing compatibility of address and control pins.
Each memory access must be qualified with a low
transition of /CE. In many cases, this is the only
change required. An example of the signal
relationships is shown in Figure 2 below. Also shown
is a common SRAM signal relationship that will not
work for the FM16W08.
The reason for /CE to strobe for each address is twofold:
it latches the new address and creates the
necessary precharge period while /CE is high.

I do not know exactly how HP bus do. So, I ask do you know? Or is this important?


Changing NVRAM is bullett proof operation. Ok there is battery inside chip  (or  if use NVRAM socket and low stby current RAM, or if use Maxim NVRAM controller chip), external battery).  Last time I have changed NVRAM's to HP545xx scopes they have been around or even over 20years without fail (But version HP used is bit better than usual). If NVRAM quality is same 20 year extra life for this scope is lot of.

[Wuerstchenhund]

So, I know that the NVRAM is bad (really the battery inside)

As to the bad NVRAM, I'd replace it with a FRAM IC instead another NVRAM module. Works the same and doesn't need a battery.

Do you know HP54xxx   memory handling /CE signal pass for using FRAM

If I remember right it's just a drop-in replacement for the 54500 Series scopes.

However, the later 54500 scopes (i.e. the ones with multiple knobs like the 54542A) have a clock (they use the clock in the Dallas module), which is lost when using FRAM. That's not a problem for the 54510A though, which doesn't have a clock.

[xrunner]

Thanks for all the responses. I have already ordered the NVRAM but will look into the other option. It won't be a big deal to swap the NVRAM after I mod the board with a socket for that IC. I also take note of the power supply capacitor replacement issue. I will probably take it apart today and clean the very fine black dirt out of it and take note of the caps I need.

One task I have is to repair the rear DC Calibrator output BNC, because it is so damaged I can't connect a BNC. I'm not sure why they used what is an RF-capable connection from the rear of the unit to the board for a DC signal. What I need to know is, what is the connector that they used to connect the cable to the board? Is it an SMB? I don't have any here to compare it to. Please advise. The BNC and SMB (if that's what it is) are crimp on connectors. I could buy those and re-produce the same jumper, for the sake of keeping it all original, but in theory, couldn't I just use a solder cup BNC chassis connector in place of the BNC crimp?

Thanks for the input!

[xrunner]

Proceeded to clean the power supply, crt driver board, and associated aluminum. Washed off with alcohol and dried. Re-assembled and tested to make sure I didn't jostle a component loose, still works. Completed the power supply adjustment and the CRT set-up.

Note the CRT made by Matsushita and CRT driver made by Hitachi.

Now need to pull the main board and remove the NVRAM ... 

[Smith]

You can just replace the BNC with some random BNC connector, it's nothing fancy. Be carefull not to shorten the original cable to the connector though, it's quite short if I remember correctly. I would recommend fastening the NVRAM module to the socket with a tie-wrap.

BTW, give it at least have an hour before selftest/selfcalibration. It will fail when the system havent had time to properly warm-up.

[xrunner]

You can just replace the BNC with some random BNC connector, it's nothing fancy. Be carefull not to shorten the original cable to the connector though, it's quite short if I remember correctly.

I may try to reproduce them, if not yea, I don't see what special needs are required for a DC signal there.

I would recommend fastening the NVRAM module to the socket with a tie-wrap.

I will take that under advisement.

BTW, give it at least have an hour before selftest/selfcalibration. It will fail when the system havent had time to properly warm-up.

Yep.

By the way - what's up with those front BNC nuts? I had to remove them all with long-nose pliers because I couldn't get any socket on them and an open end wrench kept slipping off. They appear to be 5/8" but the socket won't fit because of the space against the case, and a regular open end wrench seems to slip off. The flats on the nut are very small. Yuck.

Anyway - I'm pulling the main board now.

[AF6LJ]

This is off to a good start, nice score by the way.
I am looking forward to seeing your progress.

[xrunner]

This is off to a good start, nice score by the way.
I am looking forward to seeing your progress.

Thanks. Next up was the bad NVRAM IC. I removed the board and removed the old NVRAM. I then installed a 28 pin dip socket. Also cleaned the board as good as I could - it sure is a pretty board.

The whole thing is now basically stripped down. I want to remove as much of the black dust that I can, that dust that is attracted to HV areas. I'll probably just dip the case in the bathtub. I also plan to clean the CRT as much as possible.

[xrunner]

Gave the old CRT a thorough cleaning. Made a nice pile of dirty alcohol prep pads (I love those things). HV really attracts a lot of that fine black dust.

You can see the burn-in on the CRT - the ghosts of measurements past. I wonder what kinds of signals this scope has seen over the last 27 years - maybe if we look hard enough ...

But the cleaning went well and it looks almost like new.

[AF6LJ]

Wow!
I always turn down the intensity when the scope is not in use.
Especially on gear that I used daily at work.

[xrunner]

Wow!
I always turn down the intensity when the scope is not in use.
Especially on gear that I used daily at work.

Yep, good idea. No telling how many years it was left on all day, but really the screen seems bright and just fine.

Just cleaning the keypad assembly today. I'm posting these pictures for anyone in the future that may need to see the assembly, for whatever reason.

[xrunner]

Put the scope back together, but still waiting on the NVRAM. I wanted to test it but when I removed the old NVRAM two pins broke off the chip - pin 14 (GND) and pin 17 (DQ5). Just to see what the instrument would display, I powered it up without the NVRAM chip. You can see what the screen displays in the attachment. I'm posting that in case someone in the future needs to see what a non-functioning NVRAM chip causes (not one that simply has a bad battery).

What I did was to tack on two wires to the chip, where the small stubs were where the pins were - I was able to solder to them. I then ran the GND wire to ground, and the DQ5 wire to the socket under the chip, and inserted the chip in the socket. When I powered it up, it worked as it should (at least the same as before). 

So now I can move on to the board calibration, which doesn't require the NVRAM chip to be able to store data.

[xrunner]

I can't buy a new Schaffner filter like the old one. The only new part numbers available is this

FN 393-2.5-05-11

The original part is

FN 393-2.5-05-12

No supplier I went to had the original part number, they only sell the new part number (-11).

I eventually called the NA office of Schaffner, and the engineer said they changed the design in 1993. He gave me a copy of the change notice (please find attached). Here's the deal - the new one (the -11 model) would work when using it on 120 VAC, because those connections made by the removable switch block are the same (it connects windings in series). BUT - the 220 VAC connections are NOT the same as the old model. That's what the engineer alerted me to. Take a look at the PDF attached.

So, the question I want advice on is - do I buy the new model knowing that if somebody used it on 220 VAC something bad might happen, or do I get a used -12 model, knowing the connections are exactly the same but might have a lot of hours on it? What should I do?

 

[tautech]

By the way - what's up with those front BNC nuts? I had to remove them all with long-nose pliers because I couldn't get any socket on them and an open end wrench kept slipping off. They appear to be 5/8" but the socket won't fit because of the space against the case, and a regular open end wrench seems to slip off. The flats on the nut are very small. Yuck.

LOL
Machine a socket down or hunt for a quality thin wall model from say Snap-on or Stahlwille.

I can't buy a new Schaffner filter like the old one. The only new part numbers available is this

FN 393-2.5-05-11

The original part is

FN 393-2.5-05-12

No supplier I went to had the original part number, they only sell the new part number (-11).

I eventually called the NA office of Schaffner, and the engineer said they changed the design in 1993. He gave me a copy of the change notice (please find attached). Here's the deal - the new one (the -11 model) would work when using it on 120 VAC, because those connections made by the removable switch block are the same (it connects windings in series). BUT - the 220 VAC connections are NOT the same as the old model. That's what the engineer alerted me to. Take a look at the PDF attached.

So, the question I want advice on is - do I buy the new model knowing that if somebody used it on 220 VAC something bad might happen, or do I get a used -12 model, knowing the connections are exactly the same but might have a lot of hours on it? What should I do?

 

Google is your friend and there's some 230V units on eBay:
http://www.ebay.co.uk/itm/FN9222R-16-06-Schaffner-16A-250VAC-Mains-IEC-Filter-Socket-Panel-Mount-/182117819268
http://www.ebay.co.uk/itm/Bulgin-PS620-3A-Mains-Filter-IEC-Input-Socket-250VAC-3A-40C-OM387F-/391212205302

It is an IEC socket type right?

[xrunner]

It is an IEC socket type right?

Well yea but I'd rather get the new part and mod the socket somehow to prevent the 220 option from working than put in something that doesn't look original. I'm looking at some used original parts on Ebay also, there is a date code on the label at the bottom.

I'm also wondering if the switch block from an old model would fit in a new one and may lend itself to modification.

[tautech]

It is an IEC socket type right?

Well yea but I'd rather get the new part and mod the socket somehow to prevent the 220 option from working than put in something that doesn't look original. I'm looking at some used original parts on Ebay also, there is a date code on the label at the bottom.

I'm also wondering if the switch block from an old model would fit in a new one and may lend itself to modification.

OK but show us an image, is it switchable too? 

[xrunner]

OK but show us an image, is it switchable too? 

Yea it's switchable, give me a little bit and I'll post some pictures. I also want to hear from Wuerstchenund because he said they were still available. I sent him a PM and I'd like to know if he knows of any new old stock somewhere becasue that original part is not available as new.

Keep in mind - I know of nothing wrong with the part that's in the unit right now. I was just advised that they blow out by Wuerstchenund. Maybe it's not a big deal, how many blow out, what percent blow out? Any given part can fail. I mean the thing's been around for 27 years and the part is still working just fine and I can get the actual part (used) on Ebay right now ... 

How about this - buy a new part and epoxy the switch block in the 120 VAC position ... 

[xrunner]

I'm going to buy the new part and install it, and keep the original part. If I ever sell it I'll give the buyer the option of keeping it as-is, (it can't be used on 220), or I'll send them (or re-install) the original with the notice that some of the older parts may fail, and it can be used on 220 if the block is inserted that way.

I'm not really sure why they even changed the way the wiring works for 220, per the little wiring block. The industry must have decided power supplies were going to be designed differently at some point in time. The change notice is dated 1993.

Done deal.

Anyway, the USPS is out for delivery with my NVRAM chip so I've got bigger fish to fry for now. Thanks for the advice.