Ikegami HTM-1990R video monitor horizontal down/ no high voltage

• Ikegami HTM-1990R video monitor horizontal down/ no high voltage
  Posted by belzrebuth on 06 Dec, 2023 22:00
• Hi all,
  I came across a too good to pass deal on this non functioning monitor.
  It's in very good conditions and had a very easy life but unfortunately it has the "horizontal down" and "high voltage down" protect LEDs lit.
  The panel responds to commands etc but the screen is dead with no static.
  I would suspect the HOT (TR609, 2SC5144 in this case) is shorted as that's what typically happens with the above symptoms but I think that one is okay, haven't yet desoldered it but a quick diode test shows no direct short.
  There are three more diagnostic LEDs (15KHz [D112] not lit, 30KHz [D113] lit, 45KHz [D114] not lit ).
  5V, 12V, and -12V are okay.
  Any ideas on how to proceed would be greatly appreciated.
  service manual is here:
  https://ia802300.us.archive.org/6/items/htm-1990-r-sm/HTM-1990R_SM.pdf
  and the deflection board is page 47
  
  
• #1 Reply
  Posted by m k on 09 Dec, 2023 18:20
• Lower right has CN205, a bit left from there is PROT and either deflection can pull it down.
  
  Maybe it's actually just a horizontal problem.
• #2 Reply
  Posted by belzrebuth on 09 Dec, 2023 21:26
• That's what I'm thinking.
  It's the most probable but the big
   transistors I checked are not shorted so I'm bit puzzled on what I should check next.
  Maybe check for a horizontal drive signal maybe that's what I'm missing..
  
• #3 Reply
  Posted by m k on 10 Dec, 2023 20:11
• It can also be a fault in protection circuitry.
  A protection is a protection, no matter how it is happening.
  
  This time the signal must also go through a transformer.
  Many possibilities to go wrong.
• #4 Reply
  Posted by belzrebuth on 11 Dec, 2023 20:45
• Could you help a bit on what I should check maybe?!?
  I've never had to troubleshoot such a complex circuit, most of the horizontal faults I've encountered were blown HOTs or shorted components like caps etc or even oscillators missing but nothing like this one.
  It's a pity that the service manual does not have any DC operating points or waveforms.
  A theory of operation would also help because I'm a bit clueless here..
• #5 Reply
  Posted by m k on 12 Dec, 2023 15:31
• IC301 pin 2 must be pulsed or there will be a fault.
  
  Actual function side of the circuit has too high voltages, so transformer T603 is attenuating.
  Pulsing must be high enough to be able to trig pin B, so close to 4V.
  
  If no pulses are present the situation is clear, that is the cause, maybe not the first.
  Above relay and FET circuits are static LC time changers and not necessary, pulsing must always be.
  Capacitors C639 and C640 are the center, both ends must have a galvanic connection to the end, supply voltage and ground.
  At least one capacitor must also be present, more or less, here those FET circuit capacitors can act as alternatives, if activated.
  
  H. DEF DOWN LED driver 74HC123 (IC301) is a retriggable monostable.
  When its pin 4 goes down pin 13 must go up, that is a no protection situation and LED is off, since TR301 is also off.
  This can happen only after monostable is activated and RC timed (pins 14 and 15) time has not passed.
  Start of this is a rising edge of B AND NOT A if NOT NOT CLEAR, since the connection is as it is only B (pin 2) is changing.
  So when B goes up Q goes also up and stays there until time out or retriggering by new rising edge of B, and so TR303 base is not pulled down and PROT is not pulled up.
  Here those boxed transistors are inverters and double diodes are switches.
  R301 before B is a pull down, so if nothing happens Q stays down and it's always a fault.
  D301 is overvoltage protection and C301 a DC filter.
  
  A bit left of IC301 is IC604.
  There FBP OUT TP606 is similar to H.DEF DOWN but not inverted and activated by pin 1 NOT A.
  So main feedback FlyBackPulse TP606 pulsing means that indicating monostable and at least partial T602 are operational.
  
  All down from TR609 is MUTE, it can also stop the party.
• #6 Reply
  Posted by belzrebuth on 14 Dec, 2023 18:11
• Thanks so much for your help.
  IC301 is indeed not pulsing (0V) and pin 4 is high.pin 15 is high and pin14 is low.
  FBP OUT (TP606) is also high and not pulsing..
  So should I start checking all the FETs next to the relays?
• #7 Reply
  Posted by m k on 14 Dec, 2023 21:14
• First you must find something that pulses.
  Since FBP is also off the whole thing seems to be off.
  
  Can't say why TR609 is hot if it is not driving anything, maybe it tries but can't.
  Check AutomaticFrequencyControl from the other side of T602,
  there should be a DC voltage over C626, same with C628 and 629.
• #8 Reply
  Posted by belzrebuth on 15 Dec, 2023 07:30
• The most weird thing happened, just left the monitor on for a while and I saw the horizontal down led going off and then the high voltage went off as well, and I got the monitor to start up..
  Then I got some pincushion distortion and HV collapsed.
  After a few power cycles I got an image and regular power ups like nothing's on.
  
  I suspected that I have bad capacitors somewhere so I thought I will leave it to completely discharge and come back.
  Left it for 5 hours and it starts again with no delay so I'm puzzled on what the problem was.
  
  So my actual problem now is that I still have pincushion distortion on one end (from the left) but the right border is fine.
  It seems that my problems are getting fewer..I'm still thinking I may have some bad capacitors due to the pincushion distortion and that would partially explain the previous error..
• #9 Reply
  Posted by m k on 15 Dec, 2023 11:32
• Pincushion or one sided barrel distortion?
  
  Horizontal center sides have their own capacitors.
• #10 Reply
  Posted by belzrebuth on 15 Dec, 2023 11:38
• Hmm it didn't last long..
  I left it a while unplugged turned it on worked for a bit (less than a minute) and now the horizontal down LED is not lit but HV collapsed and HV led lit again..
  I think there is still something going on with this as it's expected.
  Maybe the pincushion was just a side issue and the main issue is still there.
  
  edit: I uploaded pictures of TP210 and TP209 when HV led is lit and horizontal LED is not lit.

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• #11 Reply
  Posted by belzrebuth on 15 Dec, 2023 12:12
• Quote from: m k on 15 Dec, 2023 11:32

  Pincushion or one sided barrel distortion?
  
  Horizontal center sides have their own capacitors.
  

  
  Ιt was pincushion but it's not in hourglass shape as usual looks distorted only on the left side
  (see picture, nevermind the greenish tint the monitor was set for RGB and I was inputting a component signal)
  

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• #12 Reply
  Posted by belzrebuth on 15 Dec, 2023 12:30
• I've left it on for a bit and I returned to find that T602 was burning hot and smelling.
  I hope it's not permanently damaged.
  Apparently something before or after it has a fault.
  I haven't yet checked the board with the flyback transformer.
  
  edit: This time the HOT is shorted so it must have been the "primary" side of T602 that got shorted..I wonder if it's anything else that's at fault here or it was the horizontal transistor all along that was misbehaving..I will order a replacement FJL6920TU which seems like a proper substitute for the 2sc5144.
  Could have been only this one that was partially at fault here? How would it fail short otherwise?
• #13 Reply
  Posted by m k on 15 Dec, 2023 18:04
• Only thing that can turn H.V DOWN LED off is IC1 MSPAD402 from HV OUT board.
  HV_OFF comes from deflection type selector chip and disables HV_DRV TP210.
  So some sort of a protection thing is happening.
  
  Since HV_OFF and H.DEF DOWN activated PROT are equal we can't say how the original situation really was.
  I'd say that missing horizontal deflection was the cause.
  
  I'd also say that the source of the fault is from the primary side of T602.
  Secondary side has very little of what could do things in the picture.
  T602 itself is also less probable as a source, it would more likely change the deflection differently.
  
  Burning hot is not necessary show stopper for a transformer, but smell is a bit overboard.
  
  Even if transformer is gone it's not necessary the end, it's a pretty simple thing.
  Some elbow grease for sure, and nerves, but pretty simple still, those new windings.
• #14 Reply
  Posted by belzrebuth on 15 Dec, 2023 21:45
• Let's just wait for the new transistor if it burns right away then it's something else if not maybe that's what it was needed right from the start.
  I only hope for the transformer to be okay.
  Shouldn't have let it toast for that long.
  I will post when the new transistor gets here!!
• #15 Reply
  Posted by belzrebuth on 23 Dec, 2023 15:26
• I replaced the HOT and we are back to both LEDs lighting up..
  I'm puzzled on why did it work even for a short time maybe the pincushion thing is a clue because there was always a left issue so I may need to check that or the reason the transformer got so hot.
• #16 Reply
  Posted by m k on 26 Dec, 2023 18:21
• TR609 can be already weakened earlier and just gave up now.
  Is its temp up now or is it pulsing between TP603 and 604?
  
  T602 became hot because TR609 was shorted.
  
  First you need a better test picture.
  Now it seems that east/west correction is only partially off.
  
  Background on top has different shades.
  Are they real and should they be "straight" down?
  
  Most right seems to be above the vertical center.
  Maybe it's just a setup for TDA4856 IC201.
  Maybe +B is too high, that can also weaken TR609.
  
  After voltage checks you can check EW_OUT TP_208, its shape must be symmetrical.
  If it's similarly off balance as is the picture then the chip is the source.
  
  TR609 is driving H.DEF, HV_+B and T602, but it's just pulling down what DEF+B TP602 through TR606 and T602 is, so DEF_+B must be there, later +/-12V for TL082 IC601 also.
  T601 must drive TR609, so 120V must be present, 5V and -12V also for IC605.
  
  Then if MUTE is off TP602 can be on, and more on if TR604 and IC601 are pulling up.
  
  Finally AFC and H.CENT +/-Vcc must be present.
• #17 Reply
  Posted by belzrebuth on 28 Dec, 2023 12:10
• Thanks for the tips m k, I will check those when I have my high voltage back!
  But unfortunately I'm back to square one with this one.
  I have both the horizontal deflection and high voltage error LEDs on.
  
  So I could just wait again for those LEDs to be off and high voltage to come up as it did before or now my problem is solified since last time I waited too long and eventually the LOPT got burned without HV ever coming back up.
  Now I replaced the LOPT and it seems to run cool while in protect mode but I don't think I should wait for more than a minute since when it briefly worked it certainly didn't take that long.
  I need to find the first fault which is why it starts in protect mode.
  
  I ordered 2x 74hc123 and I'm waiting for those to get here anytime so I could replace those just in case one of them is bad.
  I don't know why the monitor came back up in the first place since it was starting with both LEDs on right from the start so I'm suspecting that maybe an oscillator tries to start but fail most of the time.
  It could also be a timing capacitor somewhere that is bad but those look very clean from a visual inspection.
  I will try to replace any caps close to 74hc123s and get back with my results.
  
  From a quick look when the monitor started up it seemed like it would be a really good monitor for retro stuff, looked absolutely fantastic even with all those faults so I really need to fix it somehow..
• #18 Reply
  Posted by belzrebuth on 30 Dec, 2023 22:05
• I took the measurements as advised and here they are ( I've only measured DC voltages with a multimeter ):
  Between TP603(gnd) and TP604 I have 124V. The bargraph was stable so I guess there is no pulsing.
  EW_OUT has +1.6V DC (in case of a symmetric signal this is off)
  DEF_+B TP602 is at 124V DC.
  H_CENT +-VCC are both 124.8V (diodes D614 and D615 seem to have no voltage drop as they both measure 124.8 on both their anode and cathode terminals)
  F/V_+B sits at 78V DC.
  FBP_OUT is high 5VDC.
  IC601 gets its 12 and -12V.
  12, -12 and 5V rails are there.
  I can take some scope shots as well, just took some measurements in case anything seems off..
  The monitor doesn't seem to wake on its own anymore; it just stays there with the LEDs on.
  Is there any obvious way to ensure the problem is on the deflection board?Maybe unplugging another board and test again, I'm thinking that the board the flyback sits on has a few things as well.
  Could it be that that board is the culprit?
  
• #19 Reply
  Posted by m k on 31 Dec, 2023 14:02
• Sorry about the E/W, it's East/West symmetrical.
  But it is for later.
  
  H.CENT Vcc you measure over C628 and C629.
  That 124V is their "center" value, their zero deflection energy position, what ever that really means, not important yet.
  
  But anyway, some activity is present.
  
  Since there is a protection there must also be a thing that makes it go away, it also means that there is a procedure that tries to start sort of constantly but fails.
  So what prevents the disappearance of that protection, find that and you're much closer to solution, or at least closer to initial cause.
  It can be much earlier than anything around that T602 transformer.
  
  IC201 TDA4856 is the initiator.
  Scoping there should be simple, if it's mechanically available, at least there are some test points.
  HD_IN and VD_IN must be there and then other signals start appearing.
  
  A bit below is IC204 TL7700 and its output PS1, it's a blocker.
  That must go up so TR202 can pull TR203 base down and release H.DRIVE.
  Same time it removes power from TR206 base and after C228 is dropped enough it releases HD_OUT, if other protections agree.
  So deflection is starting before HV, like you noted earlier.
• #20 Reply
  Posted by belzrebuth on 01 Jan, 2024 02:21
• HD_IN( TP204) has a 15.6kHz signal that is a bit weird as it looks like small ramps dancing around (see picture).
  I don't think this is possible to be an output of an inverter and indeed the output of the inverter is fast triggers at a rate of 15.6kHz that look healthy.
  So R205 and C207 are forming a LPF or delay circuit on the fast triggers of the original HD_IN signal?
  Their values indeed put a pole at 15.9kHz..
  I don't know why is that ;I thought HSYNC should have been like the output of the inverter.
  If HD_IN testpoint should have a square signal then we have our suspect.
  H.DEF DRV (TP209) has a proper square at 15.6kHz.
  

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• #21 Reply
  Posted by m k on 01 Jan, 2024 17:54
• Are D112-114 also 15kHz?
  
  Same RC for H and V.
  Resistor is a current limiter and capacitor a spike eater.
  
  TDA4856 pins 14 and 15 are TTL level inputs.
  Maybe TP has a bad connection.
  How is pin 11 EWDRV?
  
  Since H.DRIVE is active the thing should be ready to rock.
  TP_210 is down since protection is on, but it should have a possibility to start when protection goes off.
  How is TDA4856 pin 1 HFLB?
  
  T601, TR609 and T602 should also be active, because of H.DRIVE, so AFC should also be something.
  How are H.CENT -/+Vcc?
• #22 Reply
  Posted by belzrebuth on 22 Feb, 2024 15:19
• Today I replaced the main IC (TDA4856)..I've been waiting for it to arrive for a longtime now.
  Still nothing though..
  So more troubleshooting is needed as it seems..