Date   

Re: Is my Tek 468 beyond repair?

John
 

Chuck, thanks. I will have a look at the crystal driver. Will need to remove that board.

Regarding the processor, I get what you are saying. I put the jumper in reset mode which holds the RESET line down to ground. Processor should be halted. When I pull the jumper, it brings the RESET line back up and I am expecting the processor to start and do something, but all I get on the LA trace is RESET going up and no other activity. Even though I don't have the address lines connected to the LA, I expected to see the status of S0 and S1 change in response to a read operation and at least some ALE pulses before the processor halted again, but my understanding here is admittedly limited. I am learning as I go along.


Re: Is my Tek 468 beyond repair?

Chuck Harris
 

The scope should have no problem running 24-7 with
the case off and no fan.

You have just found a problem to fix.

Crystals that get hot have defective drivers that are hitting
them with too much power. There should be no measurable Trise
on the crystal.

Once the halt instruction happens, there will be no activity
from the processor because it will have .... halted. The only
way out of a halt is to reset the processor.

-Chuck Harris

John wrote:

Hmm, stuck the LA on it today but I see no processor cycles whatsoever.

The LA has 16 channels but I have only 8 clips, so I connected the control lines only:

RESET
S0
S1
ALE
RD
WR
TRAP
INTR
and
GND

The scan was run at 10MHz (2 x 5MHz - Nyquist).
The capture was run for 10 seconds.

The jumper was set to RST to pull the RESET line down. I hit Run in Pulseview and at the same time pulled the jumper. The RESET line goes up but nothing else happens. No change in S0/S1 states, no ALE.

Incidentally, I discovered that the clock signal was fading out. It seems that with everything open and fan not blowing the crystal gets a bit hot and stops oscillating and the signal fades. I set up an old PC fan to blow
on the board with the 5MHz crystal and monitored on the scope and repeated the test a handful of times, but even with the clock definitely running I saw no activity other than the reset line going up.






Re: Is my Tek 468 beyond repair?

John
 

Hmm, stuck the LA on it today but I see no processor cycles whatsoever.

The LA has 16 channels but I have only 8 clips, so I connected the control lines only:

RESET
S0
S1
ALE
RD
WR
TRAP
INTR
and
GND

The scan was run at 10MHz (2 x 5MHz - Nyquist).
The capture was run for 10 seconds.

The jumper was set to RST to pull the RESET line down. I hit Run in Pulseview and at the same time pulled the jumper. The RESET line goes up but nothing else happens. No change in S0/S1 states, no ALE.

Incidentally, I discovered that the clock signal was fading out. It seems that with everything open and fan not blowing the crystal gets a bit hot and stops oscillating and the signal fades. I set up an old PC fan to blow
on the board with the 5MHz crystal and monitored on the scope and repeated the test a handful of times, but even with the clock definitely running I saw no activity other than the reset line going up.


Re: TDS 684A needs recapping?

 

So I'm sending this letter from my PC rather than the phone.
Wondering if this looks any better.
Looks good to me, and I don't have to go online to see your posts now...
Jay


Re: Is my Tek 468 beyond repair?

Roger Evans
 

Chuck, John,

The insight into 8085 programming wisdom is very illuminating. I am guessing that the 160-0459 ROM is mapped to $0000 and there are many HALT instructions (hex $76) scattered through the first 100 bytes of code that look as if they are intended to catch a corrupted jump instruction that then falls through to the HALTs. The 8085 still has to execute a small number of instructions before hitting the HALT. I think the minimum would be five memory references and so five ALEs and five RDs before the HALT. It should be fairly straightforward to capture that on John's DSO.

Roger


Re: Is my Tek 468 beyond repair?

tgerbic
 

Does anyone know of a link for the download of the Tek468.zip file, which contains the service ROM bin file?

Thanks
Tony


Re: Is my Tek 468 beyond repair? Trap and Kernel test procedure

tgerbic
 

Heitor,

What are the symptoms of the two scopes and what have you already identified as problems? Perhaps that would help us figure out ways we can help you. Please keep the symptoms of each scope completely separate in your posts so we don't get them confused.

Regards
Tony


Re: Tek 4654M; No Trace, No +5V, No +95V; Help

Michael W. Lynch
 

On Fri, Sep 18, 2020 at 05:54 PM, Harrison wrote:


I confirmed in my shop notes, I did separate U550 and T550 by breaking the
connection at T550 pin 10.
Harrison,

Yes, but that action does not eliminate the rest of U550. There are other circuits in U550 that are powered through that same secondary winding of T550. That winding has 3 taps, so Pin 10 only disconnects the HV Multiplier portion of U550. If there is a fault in some other portion of U550, T550 could still be overloaded. Look carefully at the CRT schematic and you see that Pin 8 and Pin 9 drive other portions of the U550 Circuit. Even with Pin 10 disconnected, a fault in the circuitry attached to Pins 8 or 9 could cause the same failure. It is also possible that T550 itself is shorted internally. Disconnect 8-9 and 10 and see if this clears the short.

The schematic just shows a box for the multiplier. Where did you find the specs for the multiplier circuit components?
I found these values through research of what others used, a circuit simulation program and some successful experimentation. The TEKTRONICS SEMICONDUCTOR CATALOG gives some useful information for U550 and others as well. This can be found here: http://w140.com/tek_xref_free.pdf

This is the link to the Reference materials section of TekWiki, here: https://w140.com/tekwiki/wiki/Reference_material

Should I expect that if I build a multiplier and install it with the existing U550 I should see that multiplication in the >readings and thus perhaps rule one way or the other on the multiplier and go from there?
The Multiplier only creates the HV for Post Deflection Acceleration. If the HV portion is shorted, then it will overload T550 and blow the Fuse. If you build a "Stand alone" Multiplier, the remaining circuitry in U550 must be functional. It sould to me like there is another problem inside U550. This is why I suggested removing U550 completely, if removing U550 does not clear the short, then the issue is the remaining components, such as T550, the oscillator or regulator circuitry that remains.

Good luck
--
Michael Lynch
Dardanelle, AR


Re: TDS 684A needs recapping?

Ray
 

Roger,


So I'm sending this letter from my PC rather than the phone.
Wondering if this looks any better.

I have seen my own letters from the phone since I send to all and thus getting a "Copy"
Well they're all word wrapped with missing linefeeds.

There is some strange stuff happening.....


Thanks


-Ray

On 09/17/2020 7:52 AM Jay Walling via groups.io <jayw_comark=yahoo.com@groups.io> wrote:


On Wed, Sep 16, 2020 at 02:02 PM, Ray wrote:


Roger,Thanks for clarifying that.I was getting worried there for a moment
Weird. Yeah, if I go online I have to click on "view quoted text" to see what you wrote...
For some reason, your emails to the list appear as quoted text.



Re: Tek 7854 intermittent issues

Nick Corvid
 

Alright, found a spot for -5V and checked it with both a meter and a scope, came out to -5.05V with some funky high frequency noise/ripple around 40 mV for the main body and nearly 100mV counting the weird interference. Here is a picture of what I'm talking about:

https://groups.io/g/TekScopes/photo/252782/0?p=Created,,,20,2,0,0


Re: Tek 4654M; No Trace, No +5V, No +95V; Help

n4buq
 

Harrison,

As I recall, U550 was rather easy to remove. All the pins are somewhat obvious from the trace side of the board since they're slightly larger diameter pins. They desoldered rather easily too so removing it shouldn't be too much of a problem. If the fuse still blows with it removed, then it would be easily soldered back in place if you so decide.

Note that at least two of the pins not associated with the multiplier are grounded so it wouldn't be too difficult to see where if it is the case that those caps are bad/arcing, then it would put an excessive load on T550.

Good luck with it.

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "Harrison" <buma7@comcast.net>
To: TekScopes@groups.io
Sent: Friday, September 18, 2020 5:54:31 PM
Subject: Re: [TekScopes] Tek 4654M; No Trace, No +5V, No +95V; Help

Hi Michael
I confirmed in my shop notes, I did separate U550 and T550 by breaking the
connection at T550 pin 10. After doing so F558 blew upon powering up the
scope. I was looking at pulling U550. Still working on figuring out Which
board connections are which. Looking at the schematic it appears that there
are 11 connections on U550. The schematic just shows a box for the
multiplier. Where did you find the specs for the multiplier circuit
components. Should I expect that if I build a multiplier and install it
with the existing U550 I should see that multiplication in the readings and
thus perhaps rule one way or the other on the multiplier and go from there?
I have 6.8V at the junction fo CR582 and C582. I think there should be 90
to 95V there. What drives that output of T550 (pin 2). Or should I see
that fact in itself as an indication the T550 is shorted and concentrate
there before tearing into U550?
Harriosn






TDS6604 Acquisition Board Replacement

guy_ellis_1964
 

I'm trying to restore a TDS6604 to it's former - hours of fun for the whole family!

After a few setbacks (Overheating CPU and a flat battery on the PPC board) I have the scope working 99%.
The remaining issue is a failed trigger chip on channels 1 and 2. Fortunately there is a pair of them so I could swap them and move the fault to channels 3 and 4.

It would seem that these chips are no longer available so I purchased another Acquisition board at a reasonable price from a reputable source.
I've swapped the Acq. boards but the replacement board reports error #351 on boot. When I run diagnostics / acquisition I also get a second error #372.
I really don't think the replacement Acq. is faulty as it was tagged as tested and sold as such.

Dr Google says the fix for #351 is to run SPC which I will try today.

According to the service manual a "Boot ROM and authorisation code" update is required, but there is no description on how to do this.
If anyone out there has done this replacement I would appreciate any tips.

Thanks in advance,
- Guy.


Re: Tek 4654M; No Trace, No +5V, No +95V; Help

Harrison
 

Hi Michael
I confirmed in my shop notes, I did separate U550 and T550 by breaking the connection at T550 pin 10. After doing so F558 blew upon powering up the scope. I was looking at pulling U550. Still working on figuring out Which board connections are which. Looking at the schematic it appears that there are 11 connections on U550. The schematic just shows a box for the multiplier. Where did you find the specs for the multiplier circuit components. Should I expect that if I build a multiplier and install it with the existing U550 I should see that multiplication in the readings and thus perhaps rule one way or the other on the multiplier and go from there? I have 6.8V at the junction fo CR582 and C582. I think there should be 90 to 95V there. What drives that output of T550 (pin 2). Or should I see that fact in itself as an indication the T550 is shorted and concentrate there before tearing into U550?
Harriosn


Re: Is my Tek 468 beyond repair?

Chuck Harris
 

There is one command that halts, 0166 octal, and 255 commands
that don't.

As I mentioned earlier, a wise programmer salts the unused
memory with halts, and makes the 7th interrupt vector contain
a halt, so executing 0377's (RST7) will go to that table, and
stop.

Then, if your logic analyzer is set to trip on the HALT state,
the LA will have a fairly good recording of how you got into
the weeds.

-Chuck Harris

John wrote:

tgerbic, thank you for the confirmation on those 3 pins.

So do I understand from the replies below that the processor shouldn't halt even with a corrupt Mostek ROM and I should still see pulses on ALE regardless? I found a book online that discusses the 8085 in detail and I got the same impression but this level of diagnosis is something rather new to me.

If I have the time tomorrow I will hook up the LA to some of the pins. Maybe that will reveal something. I need to prepare my laptop though with some software.






Re: Tek 4654M; No Trace, No +5V, No +95V; Help

Jeff Davis
 

Hi Harrison,

After reading your latest post, a light bulb went on. I did a quick search, and found that I still have a NOS U550, P/N 152-0635-00 that I bought on eBay a couple of years ago to fix a different 465M. That unit never did get fixed (too many things wrong to be used as anything other than a parts mule), so I still have the part, unused, never installed.

Contact me off list if you're interested.

Regards, Jeff / N0DY

________________________________
From: TekScopes@groups.io <TekScopes@groups.io> on behalf of Harrison <buma7@comcast.net>
Sent: Friday, September 18, 2020 2:21 PM
To: TekScopes@groups.io <TekScopes@groups.io>
Subject: Re: [TekScopes] Tek 4654M; No Trace, No +5V, No +95V; Help

Hi Bert
I have pulled a lead on both the C582 (2.2 mF) and the C584 (2.0 mF) caps in the 95V circuit. Both are +50% -10% Spec. The C582 read 2.40 mF Good would be between 3.3 mF and 1.98 mF. The C584 read 2.46mF. Good would be between 3.0 mF and 1.8 mF. So I considered these good and reinstalled the lead. I can not seem to find a new or used U550 anywhere so I was thinking of constructing one. Unfortunately on the schematic I have I don't see values for the diodes or any spec information on the 3X multiplier. Plus I am not sure if it is good, i.e. safe and wise to construct a HV module.
So for right now I am at a loss on what else I can try or test and/or determine a good way to determine if the U550 module is good or bad.
Harrison N1FAM


Re: Tek 4654M; No Trace, No +5V, No +95V; Help

Michael W. Lynch
 

Harrison,

The problem with U550 is that it does not only contain the 1.5X HV multiplier, it also contains the DC restorer circuits and some other relevant circuitry within the module. If you look at the 465 and 465B, this other circuitry is built using discrete components on the circuit board. Building a Multiplier is not at all unsafe or unwise. I used very easy to find 2.2nf 20kV rated Caps and 50mA 20kV Diodes. I have built several and I am by no means at the top of the class in this group of individuals.

I would think that completely removing U550 from the circuit would at least stop the Fuse from blowing, IF U550 is defective. However, if the problem is in T550 or the related circuitry, then removing U550 would not correct the fuse blowing issue. If you disconnect Pin #10 of T550 to U550 and the F558 still blows, then there are either bigger issues within U550 or in T550 and related circuity. I have a feeling that you have a shorted T550 or a U550 with some fault, other than just the HV Multiplier. Just my gut feeling.

It comes to mind that It is possible U550 from that 455 might ONLY have a bad HV Multiplier and still be good in all other respects. My 455 U550 fortunately failed only in the HV Multiplier section, the remaining circuitry was still intact. So, as I recently related, I was able to build that HV section and restore function.

--
Michael Lynch
Dardanelle, AR


Re: Tek 4654M; No Trace, No +5V, No +95V; Help

Harrison
 

Hi Bert
I have pulled a lead on both the C582 (2.2 mF) and the C584 (2.0 mF) caps in the 95V circuit. Both are +50% -10% Spec. The C582 read 2.40 mF Good would be between 3.3 mF and 1.98 mF. The C584 read 2.46mF. Good would be between 3.0 mF and 1.8 mF. So I considered these good and reinstalled the lead. I can not seem to find a new or used U550 anywhere so I was thinking of constructing one. Unfortunately on the schematic I have I don't see values for the diodes or any spec information on the 3X multiplier. Plus I am not sure if it is good, i.e. safe and wise to construct a HV module.
So for right now I am at a loss on what else I can try or test and/or determine a good way to determine if the U550 module is good or bad.
Harrison N1FAM


Re: Is my Tek 468 beyond repair?

John
 

tgerbic, thank you for the confirmation on those 3 pins.

So do I understand from the replies below that the processor shouldn't halt even with a corrupt Mostek ROM and I should still see pulses on ALE regardless? I found a book online that discusses the 8085 in detail and I got the same impression but this level of diagnosis is something rather new to me.

If I have the time tomorrow I will hook up the LA to some of the pins. Maybe that will reveal something. I need to prepare my laptop though with some software.


Re: Tek 7854 intermittent issues

Nick Corvid
 

Sorry about that David, to be honest I completely forgot it existed I'll get a value as soon as I'm able.

On another note, yesterday on a whim I pulled out all the digital the boards, which I had never done before on this machine. Nearly everything looked perfect except for on the MPU board where there was an unhappy looking cap.

Board in question: https://groups.io/g/TekScopes/photo/252782/1?p=Created,,,20,2,0,0
Capacitor I mentioned: https://groups.io/g/TekScopes/photo/252782/0?p=Created,,,20,2,0,0


Re: Is my Tek 468 beyond repair?

tgerbic
 

Roger, you are correct.

Looking at my notepad, I penciled in L and L for 38 and 39. Not sure how this turned into both High. Must have got distracted. Pin 37 should be 2.5Mhz as it is one half the 5Mhz clock.
Pins 37, 38 and 39 are ok on John's 468.

Regards

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