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Re: Tek 4654M; No Trace, No +5V, No +95V; Help
On Fri, Sep 18, 2020 at 05:54 PM, Harrison wrote:
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: This is the link to the Reference materials section of TekWiki, here: 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 |
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Re: TDS 684A needs recapping?
Roger,
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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@...> wrote: |
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Re: Tek 7854 intermittent issues
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:
/g/TekScopes/photo/252782/0?p=Created,,,20,2,0,0 |
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Re: Tek 4654M; No Trace, No +5V, No +95V; Help
Harrison,
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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@...> |
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TDS6604 Acquisition Board Replacement
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. |
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Re: 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 |
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Re: Is my Tek 468 beyond repair?
Chuck Harris
There is one command that halts, 0166 octal, and 255 commands
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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. |
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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: [email protected] <[email protected]> on behalf of Harrison <buma7@...> Sent: Friday, September 18, 2020 2:21 PM To: [email protected] <[email protected]> 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 |
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Re: Tek 4654M; No Trace, No +5V, No +95V; Help
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 |
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Re: 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 |
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Re: Is my Tek 468 beyond repair?
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. |
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Re: Tek 7854 intermittent issues
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: /g/TekScopes/photo/252782/1?p=Created,,,20,2,0,0 Capacitor I mentioned: /g/TekScopes/photo/252782/0?p=Created,,,20,2,0,0 |
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Re: Is my Tek 468 beyond repair?
Chuck Harris
The 8085 doesn't halt unless it executes a 166 octal instruction.
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000 octal is one of the many NOP instructions, and 377 is a RST7 instruction, which calls the 7th interrupt vector location, and starts executing... so typically, it will just maraud through memory forever, never finding a HLT instruction. Those of us that hoped for better behavior learned to salt unused EPROM and RAM space with 166's. We also typically stuck a HLT instruction in the 7th interrupt vector location, so executing a RST7 would stop the marauding processor cold in its tracks.. Note, the 8080 is an octal machine. Its structure makes sense in octal, and nonsense in hex. The boot sequence is pretty simple, it loads the program counter with zero, and starts to execute whatever it finds there. -Chuck Harris John wrote: Roget thanks. |
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Re: Is my Tek 468 beyond repair?
The processor goes to location 0 and starts executing code on a power on reset.? Typically, the only instruction that should be at that location should be a jump to a routine that performs power on reset functions.? While the processor *could* continue executing other instructions immediately after location 0, the lowest locations are used for other interrupt conditions, and you lose the ability to use those interrupts.
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A well populated 8085 system should have a series of jump instructions starting at 0. If the processor sees nothing from the ROMS during power on startup, and reads all 0xFF, then you'll be executing an RST 7 instruction, which puts the current address (0), on the stack, and transfers execution to location 0x38.? You'll read 0xFF from that, so you'll have a continuing series of repeats of RST 7 if you can read nothing. Data from your memory should be valid at the rising edge of the RD pulse (active low). You should get ALE (address latch enable) pulses as well. Harvey On 9/18/2020 11:11 AM, John wrote:
Roget thanks. |
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Re: Is my Tek 468 beyond repair?
Roget thanks.
Yes, I was using an analogue scope and watching for any flicker no matter how slight. Might be time to break out the Rigol and try single shot mode. On the other hand without any boot code to read from the ROM the processor would just simply halt so which would presumably happen very quickly. It have been trying to find a description of the exact sequence of events the processor follows at power up, i.e. the boot-up sequence if you like, but have yet to find something on that subject. I am wondering whether your book contains such information? I tracked the GPIB interrupt input to a connector on the memory board, but couldn't fathom where it went from there. I agree with your conclusion. BTW, I realized later that the buffer in non-inverting. Pins 1 and 19 were low so the buffer should be operating. I didn't expect that 1.5V on the input would be sufficient to cause a HIGH on the output side, but as you say, leaving it open is not good practice. Perhaps there needs to be a pull-down resistor to GND, but it might work as you suggest, that is the detection fails (as the GPIB board is not present) and the interrupt is masked off. I just tried the procedure on page 28 bearing in mind the comment by "Tom" posted by Daveolla. The scope powers up without the fan running but I do get a trace, however, only CH2 seems to be displaying regardless of the input switch position so there seems to be no chopping. CH1 does not appear and its position control does not seem to do anything. Only CH2 works. On the other hand this does at least demonstrate that the failure of the digital mode is preventing a trace from running in normal operation and that in principle at least the analogue side does work. It is not entirely unexpected that there may be problems to resolve once the digital side is fixed. I have restored it back to normal operation for now. Thank you for getting the ROMs in the post. I should be able to sort out some adapters. Really appreciate the comments from everyone as well. |
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Re: Is my Tek 468 beyond repair? Trap and Kernel test procedure
The 8085 has certain address locations it goes to under certain hardware conditions.? (without me looking them up, it's in the data sheet), there's one for power on reset, the hardware traps (rst 7.5, etc), interrupts and so on.
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If you monitor the address lines on the processor (fortunately, 16 of them), then (for example) when the reset line goes active, the processor should show that the address lines go to zero (IIRC) and start to execute there.? In the 8085, you don't have vectors (the processor doesn't fetch and address from location 0, then use that to show where to execute (as in the 6800 or the 6500 series), but starts executing at that location.? Thus, the location typically contains a jump instruction which goes to actual code. once you see that the location is being jumped to, you may be able to use the higher bit of the address to monitor the triggering event if you wish. For an 8 bit microprocessor, a 32 bit is more of a minimum requirement, with 16 address, 8 data, and 8 other signals (ALE, R/W, etc). Still, you could take the highest 4 bits of the address, run them through a 74LS20, then again to invert the answer, and that would give you some indication of the address if you start to trace further. Harvey On 9/17/2020 11:34 PM, Heitor Lima via groups.io wrote:
Hi group |
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Re: Is my Tek 468 beyond repair?
I don't understand Tony's measurement of 38,39 HIGH, on my schematic pin 39 is connected directly to ground.
Tracing back the input for the RST5.5 pin, in the absence of the GPIB board there is precisely nothing connected to pin 14 of U472. Leaving a TTL input unconnected is normally not good practice, I am surprised if Tek would have done that, but unconnected TTL inputs float high and the conclusion must be that in normal operation the CPU would check for the presence of the GPIB board and if not found it would leave the RST5.5 interrupt masked off. John, when you said you had looked for a burst of activity on the cpu pins immediately after reset were you using a normal analogue scope or a scope with single shot storage? The processor activitiy could only be for 10s of microseconds and easy to miss on a normal scope. I noticed the RAM on the 8085 board is made up of 2114s, I seem to remember a thread on one of the UK forums where these were regarded as failure prone but I have no personal experience with these. The two programmed 28C64s are in the first class post (don't hold your breath). I hope making the adapter boards is not too much hassle, a lot depends on the room available. Roger |
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Re: Is my Tek 468 beyond repair?
Comparison with Tony¡¯s ¡°quick once around the processor¡±.
1 5Mhz SquarewaveConfirmed. 2 5Mhz Squarewave, half size from 5V down to ~2.5VConfirmed. 3 Low, short high pulse on power upConfirmed. 4, 5, 6 LowConfirmed. 7 500Hz digital signal with 2ms positive pulseConfirmed. 500Hz signal with 400¦ÌS pulse. Cycle width is 2ms. 8, 9 High8 = LOW, 9 = HIGH 10 100Hz digital signal with 10ms positive pulsePin is high. No pulse. 11 High, occasional negative pulsePin at approximately 0.8V. No negative pulse observed. 12 to 19,k and 21 to 33 Address/data/control constant traffic12 - 19 = HIGH 21 - 31 = LOW 32 = 1.5V approx. 33 = LOW 20 GndGround connection confirmed. 34, 35, 36 High34 = LOW 35 = HIGH 36 = HIGH 37 132Hz squarewave2.5MHz quare wave 38, 39 HighBoth LOW 40 +5V VCCConfirmed. |
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Re: Is my Tek 468 beyond repair?
Reed, thank you for the note about the switch on top of the board. I will check it out. Power supplies are OK and all voltages present. I read in the service manual about the "service ROM" and wondered whether that would still be available. I will bear you in mind should I need it.
Tom, thank you for the description of the error in the troubleshooting of the analog section. Will be carrying out that procedure soon so will bear that in mind. Daveolla, thank you for the description of the files. I contacted Bruce and he has granted me access to the server. The files are now hosted on ftps and you have to e-mail Bruce for the access details. I did find the 468.zip file but not the bigger Tek468.zip. I did find a PDF of the adapter pinout in the files section on the TekScopes group. A couple of tests for next time you are looking at the scope:Sorry, my mistake. Its at 500Hz which is as per point 5 in the test procedure, not kHz. Check that pin 14 of U472 is also high so that we are not looking at a failed U472Yes, pin 14 (gate output) is high, hence RST7.5 is high. Pin 13 (gate input) is at about 1.5V. Grounding either makes no difference. G1 (P1) and G2 (P19) are low. Measure S0 and S1 (pins 29 and 33), that might show that the CPU had executed a HALT instruction and had at least done something after Reset.S0 and S1 are both LOW which would seem to indicate a halted state. I tried monitoring both during reset/power up thinking that there should be some activity, particularly on S1 as the CPU boots and attempts to read the ROM but nothing happened - it just stayed low. |
Michael W. Lynch
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