Re: Sharp MZ-80K help needed on repair
I don't quite follow the numbers, only 8 passed, but 9 passed the high speed test?
Regardless, that sounds like quite a high failure rate. Is there any chance you can return the 'bad' ones? As I said, I have had some occasional bad ones but I have never had any problem getting the bad devices exchanged. One thing which may be worth trying is just cleaning up the edges, not the flat sides, of the pins of one or two of the 'bad' devices to see if they then pass. If your chip tester has a ZIF socket as I imagine it does then it makes contact with the thin edges of the chip pins rather than the flat sides of the pins, so the pin edges need to be clean and bright. Am I right in thinking that your chip tester passes all of the original fitted SHARP branded RAM chips? |
Re: Sharp MZ-80K help needed on repair
Also, can you try the check suggested in #13, #14 by Mark and Tim to determine whether the video display circuit is independently working? If you need more detail, don't hesitate to ask.
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Re: Sharp MZ-80K help needed on repair
Hi
I purchased 20 4116 chips and only 8 passed I have contacted him and I believe he is going to send some more out and all the sharp ram passed with the video test If you could explain it in simple terms I would appreciate it as I do not want to cause any damage to something. I did remove the CG-rom and did get a white screen but with shorting the pins I take it you mean the ground pin 16 to the data pins is that 5,6,7 10,11,12 and 13 of the CG-rom socket. Is this correct. |
Re: Sharp MZ-80K help needed on repair
Ground pin of CGROM is pin 12, you can also use pin 18 or pin 20 as they are also grounded.
With CGROM removed. As Tim said earlier use a small diameter wire to avoid widening the socket pins. Wire wrap wire is probably good for this, but if you don’t have any then use a single strand from a 7x0.2 flex cable. While the white display is shown, connect pin 12 to each of the data output pins, 9, 10, 11, 13, 14, 15, 16, 17. You should see a dark vertical band in different positions depending on which pin you ground. This should verify the output stage of the video circuit. Next try connecting pin 13 (thirteen) to each of pins 6, 7 ,8. Instead of a solid dark vertical band it should be a dashed line. With long, medium and short dashes. This will confirm the vertical row generated to the character generator. |
Re: Sharp MZ-80K help needed on repair
Many thanks sorry was looking at the wrong pinout I Will try this
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Re: Sharp MZ-80K help needed on repair
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Took CG-Rom out and as picture get white screen if I then short pins 9, 10, 11, 13, 14, 15, 16, 17 I get a white screen with lines down as second picture and if I short pins 13 to 6,7,8 I get a couple of diferent pictures last two pics.
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Re: Sharp MZ-80K help needed on repair
I think this means the shift register on the output of CGROM is working and so is the character row generator.
Either the video ram is being written with the pattern that displays vertical white lines or there is a problem with the video ram. I’ll take another look at the schematic and see if there is anything we can do to safely stop the z80 running so we know we see an uninitialised display. |
Re: Sharp MZ-80K help needed on repair
Try with the Z80 removed and the CGROM fitted. Then the video ram should have random content and the screen should show random characters.
If it still shows the same vertical lines then I think this points to faulty video ram ic41/ic42, the ls245 buffer ic43, or possibly the control logic. We can try and narrow it down further after you try the above test. |
Re: Sharp MZ-80K help needed on repair
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With the Z80 removed and CG-rom installed we get this.
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Re: Sharp MZ-80K help needed on repair
I think thats good news, probably the video ram is ok as the z80 was clearing that random data to show the vertical bars, though it should be clearing it to blank.
I’m going to make a guess that ic43 might have one bad channel, instead of writing a space character to every screen position its writing the code for a vertical line. If you have a character set listing for the mz80k we might verify that is possible. It would probably need a scope to try and verify the outputs of the buffer on the video ram side. Unless anyone else can offer a better suggestion, I think it would be worth removing ic43, test it on a chip tester if you have one, and fit a socket and a new 74ls245. |
Re: Sharp MZ-80K help needed on repair
I have today ordered a second hand oscilloscope so if you could tell me what I need to do with it when it arrives it would give me some practice on learning how to use it.
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Re: Sharp MZ-80K help needed on repair
Of course it is quite easy once you get the hang of it - and a real fascinating tool to examine things with.
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Re: Sharp MZ-80K help needed on repair
What kind is it? Does it include scope probes?
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Re: Sharp MZ-80K help needed on repair
I have nothing to contribute (sorry) but I'm loving reading this thread. It'll get fixed with the help of people on here. It's not possible to get more helpful and knowledgeable people.
Colin. |
Re: Sharp MZ-80K help needed on repair
Quote:
Pud sounds confident and capable of changing IC43 which is a common, relatively low cost IC, so I agree, remove IC43 in one piece and test it and if the tester shows it to be faulty, fit a socket and a new replacement IC43. Note to pudwink: We are assuming you have plenty of experience at removing ICs in one piece from double sided PCBs. If not, it is better to cut all the legs off the IC high up next to the IC body and desolder and remove the pins from the board individually. If you do this you deny yourself the opportunity to check / test the original IC but you are much less likely to damage the PCB while removing the IC. Don't be too despondent if replacing this IC does not in itself fix all of your problems - for one thing you need a full working set of RAMs as well, but there may be more problems waiting to be found. If so, we'll try to chase them down one by one. |
Re: Sharp MZ-80K help needed on repair
I have brought a Hitachi V525 50Mhz Twin channel oscilloscope with probes.
With the IC I do have two adjustable soldering irons one with hot air and a decent solder sucker but I will play it by ear I do not want to cause any damage to the board. |
Re: Sharp MZ-80K help needed on repair
That looks like quite a capable analog scope, it should be fine for repetitive signals, but can be a bit more tricky to set up.
Are the probes x1, x10 or switchable? |
Re: Sharp MZ-80K help needed on repair
Your 50MHz Hitachi scope would have been considered quite high end in its day, most general purpose scopes at the time would have been 20MHz. If it is coming by post or courier I hope the seller has made every possible effort to protect it from impact or drop damage.
I have a V212 which was my only scope for many years. As far as removing an IC intact from double sided PCB goes, the one really important thing to remember is, when you've removed 98% of the solder from the IC pins, never, never try to lever the IC up out of the PCB by inserting something under one end and trying to crowbar it up out of the board. If you do that the IC will come out, yes, but there is a good chance that one or more of the top side PCB pads or tracks will be torn off the board. Once you have removed as much of the solder as you possibly can the IC will still be attached by thin solder bonds where the wider upper part of the IC pins rest on the top side solder pads. What you have to do then is use a blunt wooden 'pusher' like the square end of the wooden handle of a wire brush to push the whole IC from side to side, left, right, left, right until the remaining solder bonds crack and you can just lift the IC out without any force at all. For ICs which are cheap and easily available, we normally recommend just cutting the pins off the IC, removing the IC body and then desoldering and removing the individual pins as that is much less difficult to do and less likely to harm the PCB. |
Re: Sharp MZ-80K help needed on repair
All I know about the probes is they are Hitachi AT-10AK and yes I hope the seller does pack it up well but I have had some very poor packing off sellers recently.
Well today I have cut the chip out rather than cause any damage to the board and put a socket in I could not get a SN74LS245N but got a DM74LS245N I am hopeing they are the same thing I turned on the machine but still the same lines on the screen. |
Re: Sharp MZ-80K help needed on repair
Yes the DM74LS245N is the same thing, just a different manufacturer. Bad news that didn’t work. We’ll give some directions for further debug with the scope.
When the scope arrives check for any physical damage first and power it up. With nothing connected you should be able to get two flat lines, one for each channel. Try initial settings as 1ms/div on the horizontal timebase, 0.5v/ div on each channel. Trigger select switch at the top right set to auto. Turn the brightness to about mid setting. You probably need to adjust the vertical position of each channel and possibly even the horizontal position. After you have the two lines visible, turn the brightness down and adjust the focus to get a nice clear line. If the probes have a switch, set them to x10. If they are fixed x10 they should have a small trimmer in a hole on the body of the probe, or possibly on the connector that goes to the scope to compensate for frequency response. Connect the scope probes to the scope, and check the calibration output of the scope at the bottom left of the controls, you should see a square wave at this point. Adjust the vertical and horizontal settings of the scope so the square wave is about five divisions height and width. If the probes are x10, adjust the trimmer on the probe, this should change the shape of the rising edge of the square wave. You want to adjust this for as square a shape as possible, flat at the top with no overshoot. Each probe should be calibrated like this for the channel its going to be used on, then avoid swapping them, or calibrate again after swapping. |
Re: Sharp MZ-80K help needed on repair
Did you read the contents of MROM to verify it contains the correct code?
If its blank and reads FF, this would be a RST 38 instruction, pushes program counter to the stack then starts executing from 0038, if thats also FF this writes every memory location with 0039 and might look like its clearing the screen to a fixed pattern. |
Re: Sharp MZ-80K help needed on repair
I do not have a setting for a 2332 chip so used 2732 settings to read and it is showing blank with these settings but can you tell me if a different chip setting is required to read it please let me know.
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Re: Sharp MZ-80K help needed on repair
I think reading a 2332 as if it were 2732 should show FF from 000 to 7FF, but the contents from 000 to 7FF of the 2332 should be seen at 800 to FFF.
Reading a 2332 as a TMS2532 should work, if you have that option. |
Re: Sharp MZ-80K help needed on repair
XGPRO does not have TMS2532 either reading it as a 2732 shows FF all the way
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Re: Sharp MZ-80K help needed on repair
If you want to be sure about the MROM and you don't mind parting with it for a few days I can read it for you and say for sure whether it is faulty. PM me if you want to go that way. (I wouldn't ask or expect anything for doing that).
Alternatively, it is possible to make an adaptor which will allow you to read the 2332 as though it is a 2732 by rearranging the wiring of several of the pins. If you already feel that the original MROM device is dud there is a forum member here (1980s_john) who was recently able to supply programmed TMS2532 EPROMs programmed with any code of your choice, hopefully he still can provide that service. Try PMing him for details of availability and cost. You would need to be able to email the correct code to him or point to the relevant file on the internet somewhere. https://www.vintage-radio.net/forum/member.php?u=1784 |
Re: Sharp MZ-80K help needed on repair
Many thanks for your kind offer but as the rom itself is not in the best shape corroded legs and one broke off so had to replace it.
I think if I could get a replacement somehow even if it's not the fault it might be better so I have sent a message to 1980s_john and see what he says. It is a shame I can't burn one myself as I enjoy creating things myself if I can. |
Re: Sharp MZ-80K help needed on repair
There is another way, look in the usual places and you will find adaptor PCBs which are designed to allow a 2732 to be plugged into a socket originally meant for a 2332/2532. You program the code into a 2732, plug it into the adaptor and then plug the 2732+adaptor into the socket meant for the original ROM. I don't recall the adaptors being especially cheap, but maybe you could look at the commercially made ones and knock one up yourself. Either way, that would be a way for you to progress without having to rely on third-party help. I completely understand when you say you would prefer to do as much of the actual hands-on work as you can yourself.
If you wanted to make it look neater later you could always get a 2532 programmed at that point. |
Re: Sharp MZ-80K help needed on repair
right I have gone for plan b I have another programmer coming tommorow that will do 2532 eproms.
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Re: Sharp MZ-80K help needed on repair
Got the new programmer and monitor rom still shows as blank so I am hopeful this could be the cause.
Have some 2532 EPROMs on the way and will see if I can program one up. |
Re: Sharp MZ-80K help needed on repair
Probably not a good time to ask you this, but do you have an EPROM eraser? Any second hand devices you buy may not necessarily be blank (so do a 'blank check' before you try to programme them).
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Re: Sharp MZ-80K help needed on repair
Hi all
Oscilloscope has turned up today I have turned it on and set it to get two lines on the screen connected the probes set them at 10x but get nothing when I connect the tip to the .5v cal I assume the ground wire of the probe needs to be connected to the ground point on the front of the oscilloscope but tried it with and without but just two straight lines Am I doing something wrong. |
Re: Sharp MZ-80K help needed on repair
Is there an AC/DC/GND switch on each channel? Try setting both to AC or both to DC.
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Re: Sharp MZ-80K help needed on repair
Yes it has and that worked getting a reading now.and answer to earlier question got a eprom eraser all the way from China turned up Saturday.
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Re: Sharp MZ-80K help needed on repair
Sounds like you will be better equipped than we are for this sort of work by the end of the week. Have you managed to find the MROM code? I haven't looked but I assume the same site which had the CGROM code also has that code as well.
Edit: Yes, I see it under the same area as the CGROM code. |
Re: Sharp MZ-80K help needed on repair
When you calibrate the scope probes use the dc setting for both channels.
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Re: Sharp MZ-80K help needed on repair
Problem is If I get this working I will have all the equipment and nothing to use it on just waiting on the EPROMs coming and see what happens next.
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Re: Sharp MZ-80K help needed on repair
Bear in mind that even if you replace the apparently dud MROM the system still may not do anything sensible until it has a full set of known good RAM.
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Re: Sharp MZ-80K help needed on repair
I am hoping With the two lots of ram the seller sent me the replacement lot only 6 out of the 14 passed fully and he said I am the first buyer out of selling 300 of these drams to say there was an issue so I don't know,and I have found a batch of 7 I brought six years ago I did not know I had so should be just enough.
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Re: Sharp MZ-80K help needed on repair
I have to ask do you have an antistatic strap and mat as the RAM's are very sensitive to handling?
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Re: Sharp MZ-80K help needed on repair
I believe (but maybe pud can confirm again) that the original SHARP branded RAMs always test OK and that's in spite of being handled just as the other non-Sharp parts are.
Pudwink, do either of your programmers also have a chip test \ RAM test mode? Alternatively, do you have another computer, like a Spectrum, which you could test the non-Sharp RAMs in? Also did you try what I suggested, cleaning up the edges of the pins on one RAM device which always fails and then trying it again? |
Re: Sharp MZ-80K help needed on repair
With the new memory they are not showing failed completely they are passing the high speed test but failing the retention test which the instructions state that they could still work.i did try cleaning the legs on a couple but still the same result programmer does not do memory test and yes I do have an anti static strap I have no other computers that use these drams.
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Re: Sharp MZ-80K help needed on repair
I would like to hope they are actually OK. Fingers crossed, let's hope a replacement MROM moves you forwards.
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Re: Sharp MZ-80K help needed on repair
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Hi All
The eproms finaly turned up today I have programmed one up and the good news is no more lines bad news is what is shown in the picture |
Re: Sharp MZ-80K help needed on repair
This is an interesting contrast between what you had before with the apparently blank MROM in and what you have now - essentially what you had when you didn't have the Z80 fitted (your post #59) so it looks like:-
-The video circuit is working as it is independently displaying the content of the video RAMs -The Z80 is not executing code, or it is, but not getting as far as the code which clears the screen, or it is, but the screen clear is failing due to some hardware problem. Before we dive in too deep, let's look at a few basics which will also act as a kind of 'trainer' for your scope. From the sort of things you've already done I think we can assume you know how IC pins are numbered. I'm also assuming you have had a bit of a tinker with your scope by now and know roughly how to use it, but if you need any specific help please don't hesitate to ask. As you may or may not know the ground of the scope needs to be connected to the 0V / ground of the system under investigation. You can do this either by connecting the flying earth lead attached to the scope probe to a ground / 0V point near to where you will be taking the measurement from, or the scope may have a front-panel earth socket intended to accept a 4mm 'banana' plug - if so you can take a lead from there to your system ground / 0V and that will provide the scope's ground connection to the MZ-80. Set the AC/DC/GND switch for channel 1 to 'GND', then adjust the vertical position of the channel 1 trace so that it is sitting on the lowest line on the scope 'graticule', the 'grid' overlaid on the screen. If the scope probe has a 'x1 / x10' switch on it set it to x1 for now, and turn the Volts / Div knob for channel 1 to the '1' position, not to be confused with '0.1 or .1' further around the dial. Rotate the small grey knob in the centre of the larger Volts/Div knob fully clockwise until it goes 'click' at the position marked 'Cal' - and leave it in that position. Now, set the channel 1 AC/DC/GND switch to 'DC'. Touch the channel 1 scope probe tip to a point which is known to have +5V on it and you should see the line jump five squares upwards, each square representing one Volt. If that's all working, then carry on. Let's look first at the reset input to the Z80, on IC46 (The Z80) pin 26. You can do this check with a meter, with your logic probe or with your scope, but however you do it check that pin 26 normally has a high / logic 1 voltage on it, but goes low / logic 0 when you press and hold the reset button. When you let go of the reset button it will stay low for a little bit longer, then return high. If this is not happening, report back. Using only channel 1 on the scope for now, look at the signal on pin 8 of IC7 and also at the signal on pin 8 of IC9. You should see square-waves on those two pins. If necessary, wind the Time / Division knob setting upwards or downwards in order to display several cycles of the waveform across the screen. The service manual has pictures of what the waveforms on these two pins should look like, they are the first two waveforms shown on PDF page 13 / Manual page 11. Let us know if those two waveforms are present. I think they probably are, but they will be good waveforms for you to look at while you are getting to know your scope. You may find that the waveforms don't display as a steady 'picture' but instead wander from right to left or left to right across the screen. We'll explain how to sort that out in a bit. |
Re: Sharp MZ-80K help needed on repair
I think you said the original MROM had some corroded pins, so maybe try checking the connection of each MROM pin through the socket to the pcb pads. Probably also worth doing the same with the z80.
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Re: Sharp MZ-80K help needed on repair
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For anyone following / assisting, here is a found image of the Hitachi V525 scope front panel.
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Re: Sharp MZ-80K help needed on repair
I have replaced the main ic sockets earlier so they should be fine with doing a reset there is no reset button so I take it turning it off and back on will do.
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Re: Sharp MZ-80K help needed on repair
There is a reset switch shown on the circuit diagram, left of IC31 on the circuit diagram on PDF page 28 / Manual page 26 - if it is there it may be a small switch on the mainboard rather than an external / keyboard switch. Unfortunately I don't know the machine well enough to be able to tell you.
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Re: Sharp MZ-80K help needed on repair
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Your machine doesn't have a reset switch in the position marked, (see attached?)
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Re: Sharp MZ-80K help needed on repair
No there is an option to install one but mine has not got one fitted
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