|
I have a nice high serial number (B030xxx) 495P spectrum analyzer with a defective A54 memory board P/N 671212401. I have determined that this board is defective by swapping in a known good board from another 495P I have replaced the usual electrolytics but no joy. With the defective board in the SA, it boots up as a 492AP instead of a 495P as shown via on-screen messages. The 49x series of SAs use a common base of microcomputer code, with the model no. (and corresponding firmware) determined via DIP switches on the A54 memory board. I have checked the DIP switches with an ohmmeter and these seem to be working as expected, and are set according to the service manual. The DIP switches are enabled to the data bus during boot up to allow these switch settings to be read. It appears that something in the circuit enabling these switches to the bus is not working correctly. I have reached the limit of my test equipment and diagnostic & repair skills and am looking for someone who might be able to diagnose and repair this A54 memory board, or, looking to purchase a known good A54 board with v9.7 firmware. Any guidance much appreciated.
Rick
K8EZB
|
I only have the user manual for that model, but the SA has to read the switches, usually through a latch that is polled at startup. That is where I would start troubleshooting.
Michael A. Terrell
toggle quoted message
Show quoted text
-----Original Message----- From: Rick Boswell <frboswell@...>
Sent: Jul 24, 2018 12:55 PM
To: [email protected]
Subject: [TekScopes] Tek 495P A54 Memory Board Repair
I have a nice high serial number (B030xxx) 495P spectrum analyzer with a defective A54 memory board P/N 671212401. I have determined that this board is defective by swapping in a known good board from another 495P I have replaced the usual electrolytics but no joy. With the defective board in the SA, it boots up as a 492AP instead of a 495P as shown via on-screen messages. The 49x series of SAs use a common base of microcomputer code, with the model no. (and corresponding firmware) determined via DIP switches on the A54 memory board. I have checked the DIP switches with an ohmmeter and these seem to be working as expected, and are set according to the service manual. The DIP switches are enabled to the data bus during boot up to allow these switch settings to be read. It appears that something in the circuit enabling these switches to the bus is not working correctly. I have reached the limit of my test equipment and diagnostic & repair skills and am looking for someone who might be able to diagnose and repair this A54 memory board, or, looking to purchase a known good A54 board with v9.7 firmware. Any guidance much appreciated.
Rick
K8EZB
|
The switches are enabled to the data bus via tri-state buffer and an enable signal that occurs just once during boot up. Challenging to trouble shoot with my limited test equipment. And, if the buffer is bad, I lack the desoldering gear necessary to change it.
|
Where are you located? Someone on the group may live nearby. I would offer to replace it for you, but I can't get to my workbench until I finish disposing of the things my family stored in the building.
Michael A. Terrell
toggle quoted message
Show quoted text
-----Original Message----- From: Rick Boswell <frboswell@...>
Sent: Jul 24, 2018 1:38 PM
To: [email protected]
Subject: Re: [TekScopes] Tek 495P A54 Memory Board Repair
The switches are enabled to the data bus via tri-state buffer and an enable signal that occurs just once during boot up. Challenging to trouble shoot with my limited test equipment. And, if the buffer is bad, I lack the desoldering gear necessary to change it.
|
Well ¡, I don't yet know that it needs to be replaced. The buffer IC may not be the problem and I don't want to begin changing parts until I have a more conclusive idea as to which part to change. Located NH. What I am looking for per first post is someone who can trouble shoot & repair, or supply a known good board.
RB
|
On Tue, 24 Jul 2018, Michael A. Terrell wrote: It is simply astonishing how helpless some people are :) If one wants to replace a DIP IC he doesn't need _ANY_ specialized desoldering equipment. Just cut all pins as close to the case as possible, throw away that brick and pull the remaining pin stubs one by one using soldering iron and tweezer. Then use desoldering braid to clean the holes from remaining solder and the board is as good as new ready for a replacement IC. No special desoldering tools needed and no such tools make better job. The only case when one would require such tools is removing an IC undamaged for further inspection or reuse. In his case it is totally unnecessary because replacement buffer IC cost pennies so it is not even worth bothering with checking a suspicious one -- just yank it out and replace with a new one. Where are you located? Someone on the group may live nearby. I would offer
to replace it for you, but I can't get to my workbench until I finish
disposing of the things my family stored in the building.
Michael A. Terrell
-----Original Message-----
From: Rick Boswell <frboswell@...>
Sent: Jul 24, 2018 1:38 PM
To: [email protected]
Subject: Re: [TekScopes] Tek 495P A54 Memory Board Repair
The switches are enabled to the data bus via tri-state buffer and an
enable signal that occurs just once during boot up. Challenging to
trouble shoot with my limited test equipment. And, if the buffer is bad,
I lack the desoldering gear necessary to change it. --- * * KSI@home KOI8 Net < > The impossible we do immediately. * * Las Vegas NV, USA < > Miracles require 24-hour notice. * *
|
To be fair, some of the members are just getting into electronics. I've been at it for over 50 years. At one point I spent eight hours a day testing new circuit boards and repairing the bad ones. My work was better the the two women in rework, and they had better toys than my couple Ungar Loner irons.
For my own work, I prefer a vacuum desoldering iron. In days past I replaced thousands of bad DIP ICs with a Radio Shack desoldering iron. I did use some wick for desoldering, but I used regular copper braid and liquid RMA flux because it does less damage. NASA referred to it as 'wet wicking' and recommended it because it caused less damage to circuit boards. Also, when you trim the used part of the braid, leave about half the width of the wick of used wick. This allows you to transfer the heat faster, and starts the capillary action faster.
I recovered and sold thousands of 256K RAM chips back in the 286 computer days with a solder pot. We sold them for $2.75 each, and we had people begging for them because there was a world wide shortage on the spot market. We would get boards with 144 of them, and I could remove all of them from a board in under five minutes with minimal or no damage to the PCB.I used surface tension to have the solder slightly higher than the edges of the solder pot, and a special pair of pliers or a long, thin stainless steel rod that was ground flat at the end to slip it under the ICs.
Michael A. Terrell
toggle quoted message
Show quoted text
-----Original Message----- From: Sergey Kubushyn <ksi@...>
Sent: Jul 24, 2018 3:07 PM
To: [email protected]
Subject: Re: [TekScopes] Tek 495P A54 Memory Board Repair
On Tue, 24 Jul 2018, Michael A. Terrell wrote:
It is simply astonishing how helpless some people are :)
If one wants to replace a DIP IC he doesn't need _ANY_ specialized
desoldering equipment. Just cut all pins as close to the case as possible,
throw away that brick and pull the remaining pin stubs one by one using
soldering iron and tweezer. Then use desoldering braid to clean the holes
from remaining solder and the board is as good as new ready for a
replacement IC. No special desoldering tools needed and no such tools make
better job.
The only case when one would require such tools is removing an IC undamaged
for further inspection or reuse. In his case it is totally unnecessary
because replacement buffer IC cost pennies so it is not even worth bothering
with checking a suspicious one -- just yank it out and replace with a new
one.
Where are you located? Someone on the group may live nearby. I would offer
to replace it for you, but I can't get to my workbench until I finish
disposing of the things my family stored in the building.
Michael A. Terrell
|
Unless it's an expensive IC, troubleshooting a circuit like that is difficult since it is only read once while the SA is booting up. That's why most people would just change a gumdrop IC to attempt the repair. There isn't much else that could cause an error like that.
I used to spend full days testing and repairing MC68340 based embedded controller boards That IC is part of the Motorola 68000 family.
I am in Florida. I am looking at a portable shed to use as a new shop until the 1200 square foot shop is usable.
Michael A. Terrell
toggle quoted message
Show quoted text
-----Original Message----- From: Rick Boswell <frboswell@...>
Sent: Jul 24, 2018 2:48 PM
To: [email protected]
Subject: Re: [TekScopes] Tek 495P A54 Memory Board Repair
Well ¡, I don't yet know that it needs to be replaced. The buffer IC may not be the problem and I don't want to begin changing parts until I have a more conclusive idea as to which part to change. Located NH. What I am looking for per first post is someone who can trouble shoot & repair, or supply a known good board.
RB
|
Now sorry I posted here after the responses received so far. I didn't ask for advice on how to repair the board, or comments on my helplessness, but rather, a pointer to someone (knowledgeable) who could troubleshoot and repair, or supply a replacement board.
I have 60+ year background in electronics, mostly telecom and computing, along with three degrees in electrical engineering. I have no doubt I could remove the IC in question, and have done so on other equipment where I have significant hands on experience. However, the board in question is a very densely packed multilayer board with a mix of surface mount, radial lead, DIP and other devices. In examining the circuit diagram, there are many potential causes for the problem I am seeing other than the tri-state buffer, including the possibility of damaged traces due to leaking electrolytics. I would surmise from examining the circuit diagram that the buffer IC may be the least likely cause of the problem. I am seeing this possibly irreplaceable board for the first time ever and feel it prudent to find someone experienced at diagnosing and repairing Tek 49x series SAs rather than just diving in and "yanking out" parts without good cause. Without this board the SA is junk, and there is no point in possibly making the situation worse. A little finesse and relevant experience go a long way, and someone who has done this before will find and fix the problem sooner than someone who hasn't. Compounding the problem is the dense packing of boards inside the SA. Getting a probe on various test points is practically impossible without soldering a lead to the board to bring the signal out (unless one has an extender board).
So, thanks for taking time to post. Happy to receive your suggestions for a repair facility or replacement board.
|
Sorry on behalf of the group for the "helpless" comment. That was uncalled-for when you don't know who's at the other end of the conversation, or what their abilities/handicaps might be.
That being said... I'm surprised that the problem isn't your DIP switch. Those are very common failure items on these units. If you haven't gone back and double/triple-checked that switch, I'd definitely do so before going any further. Unlike the IC, I do believe it's a good idea to reflexively replace those DIP switches whenever you're working on the boards that include them. Same with the one on the back, if you think you will ever want to use the GPIB port for anything. Although Sergey's tip about cutting the leads on the IC won't be as effective for removing the DIP switches, it's still a valid strategy if you crush the plastic body with pliers and pull it off first. A Dremel tool is also a good way to go.
Working without extenders, it's sometimes helpful to tack-solder a few 'probe wires' onto various device pins to bring the signals out for monitoring. The extenders are nice to have -- and almost mandatory for some procedures -- but unfortunately they're not always available.
-- john, KE5FX
toggle quoted message
Show quoted text
-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of
Rick Boswell
Sent: Tuesday, July 24, 2018 4:06 PM
To: [email protected]
Subject: Re: [TekScopes] Tek 495P A54 Memory Board Repair
Now sorry I posted here after the responses received so far. I didn't ask for
advice on how to repair the board, or comments on my helplessness, but
rather, a pointer to someone (knowledgeable) who could troubleshoot and
repair, or supply a replacement board.
|
John,
Thanks for your reply. I'll check the DIP switches again. Thanks for the tips on removing these switches - will be helpful if I do the repairs myself. Norway Labs ( ) does currently offer extender boards for the 49x series, so I will order a set.
RB
|
On Wed, 25 Jul 2018, Rick Boswell wrote: John,
Thanks for your reply. I'll check the DIP switches again. Thanks for the
tips on removing these switches - will be helpful if I do the repairs
myself. Norway Labs ( ) does currently offer
extender boards for the 49x series, so I will order a set. Quick note about those extenders from Norway Labs -- they are OK and work for repairs (I refurbish 492BP/494AP instruments on a regular basis and use those) but one should be very careful when putting a board on those extenders. They are not keyed, there is absolutely no mechanical support other than connector pins, no connector shrouds and it is very easy to insert them with an offset that might cause serious damage not just to that board but also to other ones. Ask me how I know :) Other than that those extenders are OK and there are nothing better available anyway. Just be very careful and check everything twice before powering your instrument with a board on extenders. One other thing about extenders -- when putting the VR board on extenders one absolutely must follow Tektronix instructions on mechanically securing that board. That Tektronix-provided method is kinda flimsy and barely adequate but it is better than nothing. Unsecured VR module will be rocking from just glancing on it losing electrical connections via those extenders. --- * * KSI@home KOI8 Net < > The impossible we do immediately. * * Las Vegas NV, USA < > Miracles require 24-hour notice. * *
|
Sergey,
Thanks for your input on the Norway extenders. This is exactly the reason I am looking for someone who has been there and done that to repair my A54 memory board. Inside knowledge/experience important in this situation. Will use caution when using these.
I am on a mission to demonstrate that I am not helpless. Ordered the 74LS244 tri-state buffer and Grayhill DIP switches from DigiKey this AM. For less than $10 I got a lifetime supply of both. Will be a bit more complicated than I thought as the buffer is in an SO style surface mount package, not a DIP. We'll see. If I screw it up, I'll send it to you to bail me out!
RB
|
On Wed, 25 Jul 2018 08:31:48 -0700, you wrote: Sergey,
Thanks for your input on the Norway extenders. This is exactly the reason I am looking for someone who has been there and done that to repair my A54 memory board. Inside knowledge/experience important in this situation. Will use caution when using these.
I am on a mission to demonstrate that I am not helpless. Ordered the 74LS244 tri-state buffer and Grayhill DIP switches from DigiKey this AM. For less than $10 I got a lifetime supply of both. Will be a bit more complicated than I thought as the buffer is in an SO style surface mount package, not a DIP. We'll see. If I screw it up, I'll send it to you to bail me out! The SO style makes it both easier and more complicated. I use a metcal iron with a very specific desoldering tip for SO width packages. If you're not familiar with metcal, it's a very nice temperature controlled system with a 30 mhz oscillator sending power down a flexible cable to a small wand with a plugin tip. Amazon sells replacement tips, and I've found the Thermaltronics tips to be an exact replacement, but not available in all configurations. Pace makes equivalents, I'm sure as do other manufacturers. Hot air desoldering can work, but you have to be careful not to blow all the other chips off the board, and to not overheat anything. Not sure that you mentioned if you'd been playing with surface mount or not. I have transitioned to surface mount exclusively (where practical, still use through hole pin headers) for new designs. It was a matter of both size and the consequence of the chips simply not being available in anything other than surface mount. Not sure that I want to go back.... Removing a 100 pin TQFP chip with metcal equipment can be quite easy, and done within a few seconds. Others have used a product called chip-quick, which is apparently a low melting point bismuth solder that reduces the melting point of the existing solder and makes desoldering easy. A decent desoldering tip might be made with a length of brass channel and a conventional soldering tip. You could even use a destroyed tip since you will be attaching the channel to the tip and don't care about the tip tinning. Thought of another technique which will work. You use solder wick to suck up all the solder on the pins. This may or may not completely move the solder between the pin and the pad. Using a dental tool, while heating the pad, gently lift the pin off the board on one side. it should just lift and not stick at all. If you have a soldering tool with a very wide (but temperature controlled) tip, then you could do an entire side at a time, simply (and gently, of course) lifting the chip body. Repeat with the other side and the chip is off. Works well with two sided chips. Again, VERY gentle is the trick. I'd suggest practicing with things like old cable boxes first, if you're uncertain with the technique. Perhaps a brass bar and a soldering iron tip would work well. At any rate, good luck on this. Hope that others might benefit from the advice. Harvey
RB
|
Pretty clear you're not helpless!
For what it's worth, I find pulling a SOIC is simple with basic tools, I use solder wick along all the pins first then 'ping' each pin in turn by using a scalpel point - No 3 handle with 11 blade - inserted between the pin and the next and applying a *very* slight twist behind the pin as I heat it, to lift it clear of the pad and then work my way along. I find this works and leaves the PCB clean, tidy and ready for the replacement and the removed part totally reusable in the event that it was ok after all .....not that that ever happens of course...!
Sometimes a bit of flux before you start is worthwhile, depends on the solder/solder wick condition.
Also FWIW, I concur with the comments re DIP switches, don't know why they were so unreliable (PCB washing perhaps?) but I've had to replace a significant number of the GPIB address selector switches on both TEK and HP gear, had them failed open and closed but mostly open.
Adrian
toggle quoted message
Show quoted text
On 7/25/2018 4:31 PM, Rick Boswell wrote: I am on a mission to demonstrate that I am not helpless. Ordered the 74LS244 tri-state buffer and Grayhill DIP switches from DigiKey this AM. For less than $10 I got a lifetime supply of both. Will be a bit more complicated than I thought as the buffer is in an SO style surface mount package, not a DIP. We'll see. If I screw it up, I'll send it to you to bail me out!
|
When you want to align and solder a new SOC IC, I apply a little solder to one corner pin, then position the new IC on the pads. Then I heat the pin over the pad with the solder. If it looks good, IO solder the opposite corner, then go down one side, then the other. Look for solder bridges, then it's ready to power up. If there are solder bridges, my method is to tilt the board with the row of pins running vertically. Then I apply a drop of liquid RMA rosin flux along the row of pis. Apply a drop of fresh solder on the tip of the iron, then run it down the row. It will remove solder bridges, and remove any excess solder. I used to do this to ICs with .015" center to center spacing. QA couldn't tell my rework from that done by our new automated Heller reflow oven. I recommend buying a half pound spool of Multicore .015" 63/37 solder for rework. It makes soldering these parts much easier, and a half pound will last you for years. I used it with a special .015" tip from Plato, along with a collet for an Ungar Loner soldering iron. A stereo microscope is a big help if you have bad eyes.
I saw a fair number of bad 74LS244 ICs on new boards at our production facility so I could almost replace them in my sleep. I also found them in the wrong position, or installed backwards when they came out of production.
Multicore-63-37-CRYSL-502-3-015DIA-28SWG-Henkel-LOCTITE
Michael A. Terrell
toggle quoted message
Show quoted text
-----Original Message----- From: Adrian <Adrian@...>
Sent: Jul 25, 2018 12:10 PM
To: [email protected]
Subject: Re: [TekScopes] Tek 495P A54 Memory Board Repair
Pretty clear you're not helpless!
For what it's worth, I find pulling a SOIC is simple with basic tools, I
use solder wick along all the pins first then 'ping' each pin in turn by
using a scalpel point - No 3 handle with 11 blade - inserted between the
pin and the next and applying a *very* slight twist behind the pin as I
heat it, to lift it clear of the pad and then work my way along. I find
this works and leaves the PCB clean, tidy and ready for the replacement
and the removed part totally reusable in the event that it was ok after
all .....not that that ever happens of course...!
Sometimes a bit of flux before you start is worthwhile, depends on the
solder/solder wick condition.
Also FWIW, I concur with the comments re DIP switches, don't know why
they were so unreliable (PCB washing perhaps?) but I've had to replace a
significant number of the GPIB address selector switches on both TEK and
HP gear, had them failed open and closed but mostly open.
Adrian
On 7/25/2018 4:31 PM, Rick Boswell wrote:
I am on a mission to demonstrate that I am not helpless. Ordered the 74LS244 tri-state buffer and Grayhill DIP switches from DigiKey this AM. For less than $10 I got a lifetime supply of both. Will be a bit more complicated than I thought as the buffer is in an SO style surface mount package, not a DIP. We'll see. If I screw it up, I'll send it to you to bail me out!
|
On Wed, 25 Jul 2018 17:10:29 +0100, you wrote: Pretty clear you're not helpless!
For what it's worth, I find pulling a SOIC is simple with basic tools, I
use solder wick along all the pins first then 'ping' each pin in turn by
using a scalpel point - No 3 handle with 11 blade - inserted between the
pin and the next and applying a *very* slight twist behind the pin as I
heat it, to lift it clear of the pad and then work my way along. I find
this works and leaves the PCB clean, tidy and ready for the replacement
and the removed part totally reusable in the event that it was ok after
all .....not that that ever happens of course...!
Sometimes a bit of flux before you start is worthwhile, depends on the
solder/solder wick condition. Yep, have to agree with this opinion, wonder why? <grin>
Also FWIW, I concur with the comments re DIP switches, don't know why
they were so unreliable (PCB washing perhaps?) but I've had to replace a
significant number of the GPIB address selector switches on both TEK and
HP gear, had them failed open and closed but mostly open.
Contaminants from the cleaning process, and that most are not sealed by any stretch of the imagination. Bet you. Harvey
Adrian
On 7/25/2018 4:31 PM, Rick Boswell wrote:
I am on a mission to demonstrate that I am not helpless. Ordered the 74LS244 tri-state buffer and Grayhill DIP switches from DigiKey this AM. For less than $10 I got a lifetime supply of both. Will be a bit more complicated than I thought as the buffer is in an SO style surface mount package, not a DIP. We'll see. If I screw it up, I'll send it to you to bail me out!
|
Grayhill makes some DIP switches that are sealed with epoxy on each pin, and I've seen them with a clear layer of tape that is to be removed after a board is cleaned. They are the types with recessed actuators.
I have some old stock of Grayhill 76RSB04. The datasheet specifies adding a 's' suffix to have them shipped with the tape. The RSB part of the stock number is for the recessed rocker.
Microdyne used these, and I never saw any bad ones.
<>
Michael A. Terrell
toggle quoted message
Show quoted text
-----Original Message----- From: Harvey White <madyn@...>
Sent: Jul 25, 2018 3:38 PM
To: [email protected]
Subject: Re: [TekScopes] Tek 495P A54 Memory Board Repair
On Wed, 25 Jul 2018 17:10:29 +0100, you wrote:
Pretty clear you're not helpless!
For what it's worth, I find pulling a SOIC is simple with basic tools, I
use solder wick along all the pins first then 'ping' each pin in turn by
using a scalpel point - No 3 handle with 11 blade - inserted between the
pin and the next and applying a *very* slight twist behind the pin as I
heat it, to lift it clear of the pad and then work my way along. I find
this works and leaves the PCB clean, tidy and ready for the replacement
and the removed part totally reusable in the event that it was ok after
all .....not that that ever happens of course...!
Sometimes a bit of flux before you start is worthwhile, depends on the
solder/solder wick condition. Yep, have to agree with this opinion, wonder why? <grin>
Also FWIW, I concur with the comments re DIP switches, don't know why
they were so unreliable (PCB washing perhaps?) but I've had to replace a
significant number of the GPIB address selector switches on both TEK and
HP gear, had them failed open and closed but mostly open.
Contaminants from the cleaning process, and that most are not sealed
by any stretch of the imagination. Bet you.
|
If anyone is having trouble with replacing components, maybe try
Chipquick low temperature alloy.
Recently I came into an obscene hoard of that stuff, and found that it
works rather well.
I don't really use it, I have the tools and practice to replace
anything I work with (the other day I exchanged a transformer over 50
times on the same board!), but that low melting alloy makes it really
easy, even without any special tools.
I would still recommend that you get the tools and skills to do this
the old fashioned way, but if you are worried about damaging some
expensive piece of kit then this Chipquick stuff might just steady
your hand.
A colleague has even used gallium to swap parts without any soldering
at all. Not so useful for repairs, but it was a pretty neat trick as
long as you didn't jostle the board. Funny metal, that, especially if
you put some on aluminium.
ST
|
Chipquick is definitely very useful when the project calls for it.
JK
toggle quoted message
Show quoted text
-----Original Message----- From: [email protected] [mailto: [email protected]] On Behalf Of stefan_trethan Sent: Wednesday, July 25, 2018 4:36 PM To: [email protected]Subject: Re: [TekScopes] Tek 495P A54 Memory Board Repair If anyone is having trouble with replacing components, maybe try Chipquick low temperature alloy. Recently I came into an obscene hoard of that stuff, and found that it works rather well. I don't really use it, I have the tools and practice to replace anything I work with (the other day I exchanged a transformer over 50 times on the same board!), but that low melting alloy makes it really easy, even without any special tools. I would still recommend that you get the tools and skills to do this the old fashioned way, but if you are worried about damaging some expensive piece of kit then this Chipquick stuff might just steady your hand. A colleague has even used gallium to swap parts without any soldering at all. Not so useful for repairs, but it was a pretty neat trick as long as you didn't jostle the board. Funny metal, that, especially if you put some on aluminium. ST
|
Michael A. Terrell
Sergey Kubushyn