Analog O'scope purchase advice

[Mosaic]

Hi All:

I have a Rigol 100Mhz DSO and I'd like to get an analog O'scope to complement it.

Used is ok...I don't need super precision. Just a decent unit.

I was looking at the TEKTRONIX TAS485 4chan 200MHz analog OSCILLOSCOPE
and the Tektronix 2235A 100M Hz Analog 2Ch Oscilloscope
and the Tektronix 2245A Oscilloscope 100 MHz 4 Channel.

Prices on ebay range from $280 to $350 for decent units with probes.

I am open to advice... on other units as well.
It's my first analog unit.

 

[Mr RB]

Assuming they have similar features, the 200 MHz model would be far ahead of the 100 MHz model, bandwidth means a lot more on analogue scopes.

 

[Mosaic]

Thx RB...

I decided to go for a Tektronix 2465A, 350Mhz unit. About $280 bux. No probes.
Seller says it's fine...I hope so.

thx for the comment.

 

[KeepItSimpleStupid]

I think that model has power supply cap problems. Join the Yahoo Tekscopes (groups.yahoo.com) group and look through the archives. The caps leak. I think those are the models with the U800? hybrids. They are unubtainium, but fixes have been developed to aid in cooling. DO NOT work on these scopes with the covers off without external cooling.

See https://www.eevblog.com/forum/testg...n/?PHPSESSID=16c18f65531843aa131b925d4ac97a73 for a teardown and fix for the Hybrid.

 

[Mosaic]

I really appreciate those tips KISS. I did come across the blog in google search.
I guess i can either fab an alum heatsink or place an extractro fan on the vent to help with that IC.
As for the power supply caps....this is the linear or the switching supply you're concerned about?

If they're serviceable I suppose I could replace them as a safety measure.

 

[Mr RB]

Just replace some caps and then stick a big fan on the back of it? You can get all those high CFM fans now that are quiet and cheap.

 

[KeepItSimpleStupid]

Go through the threads at yahoo groups. **broken link removed** Here is a link from searching there: http://www.bestelectronicarticles.c...ix-2465b-oscilloscope-restoration-repair.html

They also mention that the X2 and Y2 caps go bad. These are the ones on the AC line.

The really important thing is to do something about cooling the Hybrids.

 

[Mosaic]

KISS...u are Plus 2.

Sounds like I may have some work to do when that scope arrives.

From what I've seen so far on ebay those U800 go for about $100 each, used.

I see a whole mainboard with the U800 onboard for $99 now....but who knows what's wrong with it.

I guess shotgunning all the elec caps and tantalums would be a good idea on the PSU . Bad power can stress everything else.
I'd need a schematic to verify the test point voltages though. maybe the yahoo groups?

 

[KeepItSimpleStupid]

Easy enough: http://www.ko4bb.com/manuals/index.php?dir=Tektronix/Tektronix_-_2465_Oscilloscope

Join the Yahoo Group and the archive groups. I can't stress it enough.

 

[Mosaic]

KISS, would I need a function generator?
I've been delaying buying one , but in order to test calibrate etc, I might need it....what do u think?
Can u suggest one that would be adequate?

 

[KeepItSimpleStupid]

High bandwidth scopes apparently need a self-leveling pulse generator to calibrate, but you can apparently do with a function generator. I'd look at the service manual first.

Another potential issue is NVRAM and there are two ways that it can go. A Maxim IC which has two embedded batteries in it or your scope may have a rechargeable battery on board. It has been suggested that the NVRAM be copied and a new one installed or to be very careful and maintain a power supply while changing the on-board battery.

Again, check your manual/instruments.

The NVRAM supposedly has only a 10 year life. I used one long ago.

Looks like a nice scope.

 

[Mosaic]

Jameco and others on ebay sells the Dallas 1225Y 64kbit NVRAM required.
But I need a programmer to read the old & write the new chip. They only have a 10yr minimum life, so I guess I NEED to do this.


I had a look here:
**broken link removed**

Code seems simple enuf...but I have to do it in PIC asm.

Any resources for that u can point me to?

 

[KeepItSimpleStupid]

No resources on the top of my head. There apparently were some quick and dirty programmers that used a "Real Parallel Port". CNC applications and others don't work with emulated ports. Maybe with USB3 they could work. Dunno.

You really don;t have to do anything special except for proper power up/power down which should be not much more than make sure the write protect is turned off first before taking the IC out of the socket. I had a ZIF socket on the SBC computer that you could plug in a Dallas RAM to.

Bent pins on precious IC's are a real pain to deal with. ZIF is very nice, but at a minimum, I would use a machine pin socket and a good IC extractor.

You might even be able to do it with I2C.

It's really nothing but a copy and verify operation.

I'd also write a routine that computes a checksum.

This isn't going to be an EPROM programmer. It does not have to be that smart.

If you can find a 6164 RAM chip, you could possibly play. http://www.ic-on-line.cn/view_download.php?id=1785763&file=0394\um6164_4248784.pdf I've bought stuff from these guys before.

You could "practice" on these, possibly. Then, maybe move random data to the NVRAM and verify. Then insert your precious chip.

There a a lot of friendly folks in the TEKSCOPES group, that you could probably get someone there to do it for you for little or nearly nothing.

 

[Mosaic]

Serial Eprom & pickit2

Unfortunately the pickit2 can do serial eproms but the DS1225 is like the 27 series , a parallel unit.



The 2764 Eprom is equivalent to the Dallas DS1225 used in the scope.
**broken link removed**

https://www.electro-tech-online.com/custompdfs/2013/04/DS1225YPDF.pdf

The pickit 2 claims it can do the 24/25LC64...
http://www.microchip.com/wwwproducts/Devices.aspx?dDocName=en010831

This post seems to cover the potential probs....
**broken link removed**


Still need a way to copy the firmware.

Or maybe solder up my own battery backup to the Dallas chip, maybe use a pair of rechargeable series polyacene batteries direct to 5Vcc and a 3.6V lithium coin cell via a schottky as backup for the rechargeables? That way I should have a couple days after powering down the scope to change the Lithium battery w/o risking loss of the NVRAM. I mite have to insert another schotkky in the power supply pin leg of the NVRAM to keep the polyacene from discharging back into the circuit.

http://www.goldmine-elec-products.com/prodinfo.asp?number=G13133

 

[KeepItSimpleStupid]

Look here **broken link removed** when someone really got brave on a different chip.

You probably can't backup the battery from the outside. There are two small batteries inside (embedded) into the chip as I remember.

It is 27 series PIN compatable, but no programming voltage is required. This, I think, also means they are pin compatable with 6164 RAM. Of course, you can't program RAM.

EPROMS were VERY PICKY about transients on Vpp. You were not allowed to have any.

 

[KeepItSimpleStupid]

This is an interesting thread: **broken link removed** The Dallas RTC/NVRAM.

 

[Mosaic]

I'd still like to capture the calibraton data...so i'm looking at this as an option.
You mite be familiar with the name.
https://qsl.net/iz7ath/web/02_brew/17_eprom/english/pag03_eng.htm
This needs a parallel port...but I'm in luck with that.

I still have a couple older AMD machines M7VIGPRO boards with parallel ports on them. In fact my workshop PC for printing PCBs, running the Pickit2 and checking specsheets etc. is one of those. A 512K Xp3 Duron PC... One of the 2, 512K sockets died so i'm stuck with 512 left.
Also I pulled my old cable drawer (got stuff from as far back as 1990 in there) lots of parallel port & null modem DB9 & DB25 dinosaurs. Even SCSI stuff! So building this programmer maybe on the cards.

 

[KeepItSimpleStupid]

I saw this guy: http://www.armory.com/~rstevew/Public/Pgmrs/EPROM/AndrewMcCubbin/_ClikMe1st.htm

If this hassle http://www.downtowndougbrown.com/2010/10/sivava-willem-eprom-programmer-on-windows-7-64-bit/ is worth it, the programmer is cheap.

 

[Mosaic]

Thx Kiss...I ordered this one:
**broken link removed**

As it seems modern (Windows) and mentions the specific DS1225 NVRAM. I have a couple XP machines running still with P ports as I mentioned.
Also, Ive done a bit of work in car brainboxes so I like that option too!

BTW the teardown on the 2465B shows the U800 chip to be about 1.2" long and about .5" wide based on the 14pin dip next to it.
https://www.eevblog.com/forum/testgear/tektronix-2465b-oscilloscope-teardown/
I have a few Xeon all copper passive heatsinks I got on auction a couple years ago for playing with peltiers.
https://hardforum.com/showthread.php?t=1663079

I could cut one down to size (sawzall) and fabricate a shoulder spacer (piece of copper busbar) to make a snug fit for the U800 & its TAB. Lap it flat on a piece of glass and bolt it on.

Sounds ok?

 

[KeepItSimpleStupid]

It seem cheap enough. Let me know how it goes.

Early DOS and Windows: I was aware of them and set them up on Networks, but they were too expensive. I chose the Amiga at the time of 5 1/4" floppies and then a Mac Laptop running OS 8 and OS 9. I help solve very few problems with OS10. I was helping to run a Time Sharing DEC BASIC system back in the Mid 70's to late 70's. The first hardware interfacable computer I worked with was the PDP-8 and the first micro was the 6800.

It will be interesting to see if someone can make a USB3 to Parallel port adapter that would actually work.