So one thing that occurs to me having read a few other threads in here while I'm waiting for the parts..
The capacitors will be easy enough if I want to replace them (and I know about the incorrect markings for one of them..) but which way do I install the transistors and coil? There don't appear to be any (obvious) guidelines / markings on the board that indicate a specific alignment or whatever.
You should see a D shape on the silkscreen that indicates which way to mount the original ZTX650 and ZTX213 transistors, which were installed with their flat face facing the back of the D.
ZTX651/653 are pin compatible with the 650 so should be installed as above.
Depending on what you've bought to replace the ZTX213, if it's a BC213 then it should be reversed compared to the silkscreen. Always consult the data sheets and compare pinouts to be sure.
The coil can only be installed one way (unless you really force it) so nothing to worry about there.
Thanks again Balford.. that's actually pretty obvious now you've pointed it out.. must do better!
So after checking this site I ordered a ZTX651 to put in the TR4 position and ZTX750 for TR5.
Installed them both, along with the new coil, power socket, capacitor for C47 and the regulator (which needed some extra wire so I could lay it on it's side.. the pins are pretty short).
Plugged in the AC adapter.... buzzzzzzzzzzzzzzzzzzzzzzzzzzzzz... plugged in the RF cable and messed with the TV a bit... IT'S ALIVE!
The screen is extremely yellow (which you can't really tell from the pic), but it's alive!
So.. need to have a mess with the colour dials and check the memory (POKE something or other, or just load a few games ;)) and I will replace the remaining capacitors at some point but for a first attempt I'm pretty pleased with this! Many many thanks to all who have advised me on this thread. :D
! Standby alert !
“There are four lights!”
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb!
Looking forward to summer in Somerset later in the year :)
Colour twiddled, capapacitors replaced, replacement membrane, plugged in the iPod...
Woop!
Considering that's just using the RF cable, I'm really pleased with the picture quality!
In RE: to the keyboard socket, I would like to remount it to the board, but there isn't really much left of the original pins so not sure if it would be possible. The cable mount works for the moment.
So does anyone know where I can get replacement screws (or is there a handy list of the sizes somewhere so I can go buy some replacements?) Plenty of 48k+ screw sets around but nothing for the rubber key case :(
Rich (rwap) sells the keyboard molex connectors here.
I've never found an exact replacement for rubber key Spectrum cases, but what you're looking for are 3x10mm countersunk self tapping screws in black.
Some eBay RC shops sell an (almost) match as part number 81220-1. I got some a while back, they're not an exact match but close enough to fool the untrained eye :) None in the UK at the moment but keep searching.
Oh well, that didn't last long.... it's dead again!
I found that it was very hard to close the case properly with the flying keyboard lead in place, so I took it apart and soldered back to the board. No major issues with this (broke a pin but fixed it..) and this worked fine. Put the case back together properly and used the screws from my other spectrum to see if if the machine behaved itself when sealed up.
Found that the keyboard was acting up which I think was due to the membrane touching the RF module, so i put a bit of electrical tape over the module which solved that problem.
Sealed it back up again and loaded a game (3D Deathchase) for a bit. Then went to find a copy of 'el stompo' as I wanted to see a bicolour game on a real machine and at some point while I was doing this, a burning smell appeared, the coil buzzing stopped and the speccy is dead :(
Now it doesn't do anything visible when plugged in and two of the ram IC's get extremely hot. One is in the bottom left section, the other in the bottom right.
Not sure if this is the original fault manifesting itself or something else.. I don't 'think' I've caused this as it 'was' working after remounting the keyboard molex.
So I guess I need to test the voltages again, but what is this likely to be? :(
It's likely to have been the two RAM IC's that now get hot, that failed, short circuited their supply rails and took out TR4.
Voltages are likely to be out of whack, maybe a volt or two on the -5v and 12v lines but the 5v line should still be good.
Remove both IC's that have gone bad, you can order replacements from forum member bverstee from his webshop (grab 8 to be sure you have enough, just in case).
Replace TR4 (again), test voltages to ensure you've got all rails back, then replace the 4116's.
At least you've got a socketed board so this process is much less painful that it could have been :)
I don't think it's anything you've done, just a hazard with these particular models, especially when woken from a long, long slumber.
It is likely that one of your 4116 DRAM chips was degrading. The heat of operating in a closed case pushed it further towards going faulty. Then when it failed, it overloaded the internal on-board inverter (TR4) which then caused the -5V rail to fail, which may have caused further 4116 DRAM chips to fail.
Start by cutting out the hot DRAM chips...
Test for low resistance on the +12V and -5V rails. Investigate any low resistance readings. Replace all defective or suspect DRAM chips. Replace TR4, and try again....
! Standby alert !
“There are four lights!”
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb!
Looking forward to summer in Somerset later in the year :)
Ok so testing as described in the YouTube video (initial tests..) with my Multimeter set to 200k gives the following on the lower ram ics..
Upper left (-5v) 01.0
Upper right (0v) 0
Lower left (12v) 0
Lower right (5v) 0
Which kinda suggests that all three rails are dead? or will this be because the duff ram is still sat in the board at the moment.
I also checked TR4 and TR5 as per the instructions in that video and these readings seem to be in line with expecations:
TR4 - .633 & .695
TR5 - .655 & .646
RE: buying replacement chips.. I'm happy to do this, but want to be slightly more careful since it aint cheap! Is it still the correct thing to do given the above readings? I don't want my board to wreck more ram later on! :(
BTW, since one of the 'upper ram' chips is getting hot too, if I just remove this while getting it working will the machine think that it's 16k or is there more to it?
Ok, slightly answering my own question(!) removing the duff chips and checking brings me up to 48.1 on the top left pin of any remaining lower ram chip... so -5v seems to be there after all... the other pins remain as per the previous post.
Also.. what are your thoughts on buying one of these.. other than it's not as much fun? ;)
Those modules are excellent (I run both it and its sister product the Upper Ram Replacement module in one of my Speccys).
Simply a drop in replacement seeing as you're already fully socketed, and all that's then needed is to replace TR4 to restore colour (the LM1889N PAL encoder chip runs off the 12v line).
Pull all lower and upper RAM IC's for the moment (chuck the ones that get hot), get your supply rails back, then go from there...
Looking at your earlier post, looks like you took measurements with your multimeter set to resistance testing, 200k range.
Can you pull all lower RAM IC's, set your meter to read volts DC, and verify that the 5v, -5v and 12v voltages are present.
Either way, I'd lean towards junking the lower RAM you have and either buying 8 4116 replacements, or an LRR module (depending on personal preference).
Will do, sorry I was just following the 'initial tests' video which recommended testing for resistance.
If the IC's are removed, where do I test the voltages... would this be on the socket pins on the other side of the board or is there a more convenient point?
Do pull the lower RAM IC's though before testing, as the resistance measurements shown indicated that the 5v and 12v rails were shorted to ground with the IC's in place....
All voltage testing should be done with the machine powered up. No need to have a keyboard attached.
With the 4116 "lower" RAM chips removed, you reduce the load on the internal inverter / switch mode power supply circuit (TR4, TR5 and the coil etc.).
Also with the 4116 chips removed, there is no longer the chance of a missing -5V supply causing further damage, as the chips that need it are not fitted :D
So you can take your time doing the voltage readings.
The +5V is produced by the 7805 voltage regulator, which should work regardless of the state of TR4, TR5 and the coil. If TR4, TR5 or the coil is faulty, the -5V supply will be missing (around 0V) or well outside the required voltage range. The +12V supply will also be wrong, but depending on the PSU used, the mains voltage and the actual wiring on your board, may still be around 10V to 11V. Note that for these supplies to work correctly, the +5V supply must be working.
I was going to say something else, but have forgot what :o
So I will say this instead: only carry resistance tests with the power unplugged, otherwise you will get very misleading results.
! Standby alert !
“There are four lights!”
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb!
Looking forward to summer in Somerset later in the year :)
Compared to the XP Power regulators I've fitted to Spectrums, I think the one in yours is the wrong way around! The text should be facing up (unless it has worn off) when fitted to an issue 2. However, check it against the datasheet to verify the pin-out.
It's possible quite a lot of the ICs have been damaged if they've had 11V applied to them where they should have 5V.
Compared to the XP Power regulators I've fitted to Spectrums, I think the one in yours is the wrong way around! The text should be facing up (unless it has worn off) when fitted to an issue 2. However, check it against the datasheet to verify the pin-out.
It's possible quite a lot of the ICs have been damaged if they've had 11V applied to them where they should have 5V.
The text is facing up, it's just hard to see on the photo.
When viewing from above, there's a dot on the left side of the regulator. From there, Pin 1 (left) is VIn, Pin 2 is GND and pin 3 (right) is VOut.
Comments
B
zx-diagnostics - Fixing ZX Spectrums in the 21st Century (wiki)
Sinclair FAQ Wiki
Me too ;)
Where did you order the SR10S05 regulator from?
The capacitors will be easy enough if I want to replace them (and I know about the incorrect markings for one of them..) but which way do I install the transistors and coil? There don't appear to be any (obvious) guidelines / markings on the board that indicate a specific alignment or whatever.
ZTX651/653 are pin compatible with the 650 so should be installed as above.
Depending on what you've bought to replace the ZTX213, if it's a BC213 then it should be reversed compared to the silkscreen. Always consult the data sheets and compare pinouts to be sure.
The coil can only be installed one way (unless you really force it) so nothing to worry about there.
B
zx-diagnostics - Fixing ZX Spectrums in the 21st Century (wiki)
Sinclair FAQ Wiki
So after checking this site I ordered a ZTX651 to put in the TR4 position and ZTX750 for TR5.
Installed them both, along with the new coil, power socket, capacitor for C47 and the regulator (which needed some extra wire so I could lay it on it's side.. the pins are pretty short).
Plugged in the AC adapter.... buzzzzzzzzzzzzzzzzzzzzzzzzzzzzz... plugged in the RF cable and messed with the TV a bit... IT'S ALIVE!
The screen is extremely yellow (which you can't really tell from the pic), but it's alive!
So.. need to have a mess with the colour dials and check the memory (POKE something or other, or just load a few games ;)) and I will replace the remaining capacitors at some point but for a first attempt I'm pretty pleased with this! Many many thanks to all who have advised me on this thread. :D
B
zx-diagnostics - Fixing ZX Spectrums in the 21st Century (wiki)
Sinclair FAQ Wiki
Yes, if you follow the twidding instructions (service manual), you can correctly set up the colours on issue 1 and issue 2 Spectrums :p
Mark
Repair Guides. Spanish Hardware site.
WoS - can't download? Info here...
former Meulie Spectrum Archive but no longer available :-(
Spectranet: the TNFS directory thread
! Standby alert !
“There are four lights!”
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb!
Looking forward to summer in Somerset later in the year :)
Are you leaving the keyboard socket as is or replacing that at some point?
Other than that its looking good. Glad it all worked out for you :D
Woop!
Considering that's just using the RF cable, I'm really pleased with the picture quality!
In RE: to the keyboard socket, I would like to remount it to the board, but there isn't really much left of the original pins so not sure if it would be possible. The cable mount works for the moment.
So does anyone know where I can get replacement screws (or is there a handy list of the sizes somewhere so I can go buy some replacements?) Plenty of 48k+ screw sets around but nothing for the rubber key case :(
I've never found an exact replacement for rubber key Spectrum cases, but what you're looking for are 3x10mm countersunk self tapping screws in black.
Some eBay RC shops sell an (almost) match as part number 81220-1. I got some a while back, they're not an exact match but close enough to fool the untrained eye :) None in the UK at the moment but keep searching.
B
zx-diagnostics - Fixing ZX Spectrums in the 21st Century (wiki)
Sinclair FAQ Wiki
Aside from having a hex head, do you reckon these would do the job?
Might crack or split the posts inside the case :( but I don't suppose you'd know without trying them.
I found that it was very hard to close the case properly with the flying keyboard lead in place, so I took it apart and soldered back to the board. No major issues with this (broke a pin but fixed it..) and this worked fine. Put the case back together properly and used the screws from my other spectrum to see if if the machine behaved itself when sealed up.
Found that the keyboard was acting up which I think was due to the membrane touching the RF module, so i put a bit of electrical tape over the module which solved that problem.
Sealed it back up again and loaded a game (3D Deathchase) for a bit. Then went to find a copy of 'el stompo' as I wanted to see a bicolour game on a real machine and at some point while I was doing this, a burning smell appeared, the coil buzzing stopped and the speccy is dead :(
Now it doesn't do anything visible when plugged in and two of the ram IC's get extremely hot. One is in the bottom left section, the other in the bottom right.
Not sure if this is the original fault manifesting itself or something else.. I don't 'think' I've caused this as it 'was' working after remounting the keyboard molex.
So I guess I need to test the voltages again, but what is this likely to be? :(
It's likely to have been the two RAM IC's that now get hot, that failed, short circuited their supply rails and took out TR4.
Voltages are likely to be out of whack, maybe a volt or two on the -5v and 12v lines but the 5v line should still be good.
Remove both IC's that have gone bad, you can order replacements from forum member bverstee from his webshop (grab 8 to be sure you have enough, just in case).
Replace TR4 (again), test voltages to ensure you've got all rails back, then replace the 4116's.
At least you've got a socketed board so this process is much less painful that it could have been :)
I don't think it's anything you've done, just a hazard with these particular models, especially when woken from a long, long slumber.
Do keep us posted.
B
zx-diagnostics - Fixing ZX Spectrums in the 21st Century (wiki)
Sinclair FAQ Wiki
Start by cutting out the hot DRAM chips...
Test for low resistance on the +12V and -5V rails. Investigate any low resistance readings. Replace all defective or suspect DRAM chips. Replace TR4, and try again....
Mark
Repair Guides. Spanish Hardware site.
WoS - can't download? Info here...
former Meulie Spectrum Archive but no longer available :-(
Spectranet: the TNFS directory thread
! Standby alert !
“There are four lights!”
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb!
Looking forward to summer in Somerset later in the year :)
Upper left (-5v) 01.0
Upper right (0v) 0
Lower left (12v) 0
Lower right (5v) 0
Which kinda suggests that all three rails are dead? or will this be because the duff ram is still sat in the board at the moment.
I also checked TR4 and TR5 as per the instructions in that video and these readings seem to be in line with expecations:
TR4 - .633 & .695
TR5 - .655 & .646
RE: buying replacement chips.. I'm happy to do this, but want to be slightly more careful since it aint cheap! Is it still the correct thing to do given the above readings? I don't want my board to wreck more ram later on! :(
BTW, since one of the 'upper ram' chips is getting hot too, if I just remove this while getting it working will the machine think that it's 16k or is there more to it?
Also.. what are your thoughts on buying one of these.. other than it's not as much fun? ;)
http://zx.zigg.net/LRR/
Simply a drop in replacement seeing as you're already fully socketed, and all that's then needed is to replace TR4 to restore colour (the LM1889N PAL encoder chip runs off the 12v line).
Pull all lower and upper RAM IC's for the moment (chuck the ones that get hot), get your supply rails back, then go from there...
B
zx-diagnostics - Fixing ZX Spectrums in the 21st Century (wiki)
Sinclair FAQ Wiki
Sorry for all the questions, just trying to get things straight in my head.
Can you pull all lower RAM IC's, set your meter to read volts DC, and verify that the 5v, -5v and 12v voltages are present.
Either way, I'd lean towards junking the lower RAM you have and either buying 8 4116 replacements, or an LRR module (depending on personal preference).
B
zx-diagnostics - Fixing ZX Spectrums in the 21st Century (wiki)
Sinclair FAQ Wiki
If the IC's are removed, where do I test the voltages... would this be on the socket pins on the other side of the board or is there a more convenient point?
Thanks again for your help, you're a patient man!
1024MAK provided a useful guide to where the voltages are measured lately, to be found here. Have a look and let us know what you find.
B
zx-diagnostics - Fixing ZX Spectrums in the 21st Century (wiki)
Sinclair FAQ Wiki
Do pull the lower RAM IC's though before testing, as the resistance measurements shown indicated that the 5v and 12v rails were shorted to ground with the IC's in place....
B
zx-diagnostics - Fixing ZX Spectrums in the 21st Century (wiki)
Sinclair FAQ Wiki
With the 4116 "lower" RAM chips removed, you reduce the load on the internal inverter / switch mode power supply circuit (TR4, TR5 and the coil etc.).
Also with the 4116 chips removed, there is no longer the chance of a missing -5V supply causing further damage, as the chips that need it are not fitted :D
So you can take your time doing the voltage readings.
The +5V is produced by the 7805 voltage regulator, which should work regardless of the state of TR4, TR5 and the coil. If TR4, TR5 or the coil is faulty, the -5V supply will be missing (around 0V) or well outside the required voltage range. The +12V supply will also be wrong, but depending on the PSU used, the mains voltage and the actual wiring on your board, may still be around 10V to 11V. Note that for these supplies to work correctly, the +5V supply must be working.
I was going to say something else, but have forgot what :o
So I will say this instead: only carry resistance tests with the power unplugged, otherwise you will get very misleading results.
Mark
Repair Guides. Spanish Hardware site.
WoS - can't download? Info here...
former Meulie Spectrum Archive but no longer available :-(
Spectranet: the TNFS directory thread
! Standby alert !
“There are four lights!”
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb!
Looking forward to summer in Somerset later in the year :)
+5v line - Around 11
+12v line - Around 10
-5v = 0
So that would suggest that the regulator has killed itself too? :(
I'm using an XP SR10S05, rather than a standard 7805 as I don't have a heatsink that fits this board...
It's possible quite a lot of the ICs have been damaged if they've had 11V applied to them where they should have 5V.
The text is facing up, it's just hard to see on the photo.
When viewing from above, there's a dot on the left side of the regulator. From there, Pin 1 (left) is VIn, Pin 2 is GND and pin 3 (right) is VOut.