General Monitor Repair Questions

[cack01]

Hi everyone,

I will try to keep the reading short:

1. I am desoldering some parts and pulled part of the PCB up (traces and copper pad).  See attached picture.  What is the general approach to fixing this?  The scratches on the board are from me trying to get to an inner copper trace (does not seem to be one).

2.  Is there a way to test if a resistor is open without taking them out of the circuit?  Is it okay if I just leave the resistor in and look for an “OL” or “99999K” on the multimeter? Or is it common practice to always take out the resistor to test (this is what I have read).

3. What is the rule of thumb on diodes?  Rectifier diodes I can replace with the same or higher Amperage and Voltage, but what about Zener Diodes?  I think on these I have to match the breakdown voltage correctly, but I want to confirm before I go shopping.  Right now my board has 25% bad diodes is this normal?

Thank you very much for your help.

[lilshawn]

1: do you know how it was connected originally? if so a blob of solder or a small length of wire is often enough. i suspect the 2 resistors attached onto the remains of the pad to the left. scratch off the green on whats left of that pad and use some bare wire to connect everything. bending the resistors legs in that direction will also help.

2: resistors often fail visibly. (burned/cracked) if it looks okay good chance it is. resistors that get hot go out of spec. resistance increases. if they look discolored pull up one side and test it.

3: zeners usually need to be replaced with same components. it really depends on the circuit and how it's being used.

Right now my board has 25% bad diodes is this normal?

no. i suspect you aren't testing them properly. you must remove 1 leg of a diode to test it properly. surrounding circuitry can throw the test off.


how about posting the make/model and telling us the issue. You may have a simple fix.

[cack01]

hi lilshawn!

1. You are correct both resistors were on the same trace. Can I also use flux to paint a trace on the board and then use solder to remake the trace?  More of a curiosity question. I have wire already at home I can use per your suggestion.

2. will do.  No more blindly testing resistors.

3. Thanks.  I have not been taking a lead out when testing the diodes.  I figured that if the diode allowed current to flow through both directions is was bad (doesn't matter if it is in or out of circuit).  The bad diodes all allowed current to flow through in both directions. One gave me a short with zero resistance.

Now for my problem     (thank you for reading through this)

I have a Sharp/Kortek KTM-F 33 not much info can be found on these.  I have been trying for a month.

Anyway, the monitor works great when hooked up to a Jamma PCB and the picture is good.  I am now converting to a mame cabinet using ArcadeVGA 3000 -> Ultimarc video amp -> KTM-F (Composite Sync).  The issue is that whenever I change resolution or major screen changes happen I lose vertical sync.  Sometimes it is a rolling picture and sometimes the picture will need to be realigned. But I always lose sync in some way.  The Vhold pot is very sensitive to the point where just touching it will cause me to lose sync. I also have a slight bowing on both sides of the picture's bottom which I have been unable to fix with the pincushion pot.   

I contacted Andy at Ultimarc about these issues and he says it sounds like my monitor has no Vsync signal.  I believe I do have “some” signal as I can make adjustments to lock in the sync at any resolution but the signal is weak or bad.  Changing the resolution just causes all hell to break lose.  Normally I know you have to find a happy medium with your Vhold and 50/60hz pots but nothing works.  I took the Vhold pot out and it tests fine. 5.5K ohms max and multiple readings to confirm it still is adjusting correctly (linearly).

So basically I am going through each inch of the Vertical Deflection circuit to see if I can find anything. The monitor had a cap kit 4 years ago and when the locked in, the picture is appears good (except the bowing which is minimal).  I would say 80% of the solder points on the board look old. Due to this I am just going inch by inch unsoldering, testing, and resoldering. 

Any Ideas??

[MonMotha]

1. You are correct both resistors were on the same trace. Can I also use flux to paint a trace on the board and then use solder to remake the trace?  More of a curiosity question. I have wire already at home I can use per your suggestion.

Anyway, the monitor works great when hooked up to a Jamma PCB and the picture is good.  I am now converting to a mame cabinet using ArcadeVGA 3000 -> Ultimarc video amp -> KTM-F (Composite Sync).  The issue is that whenever I change resolution or major screen changes happen I lose vertical sync.  Sometimes it is a rolling picture and sometimes the picture will need to be realigned. But I always lose sync in some way.  The Vhold pot is very sensitive to the point where just touching it will cause me to lose sync. I also have a slight bowing on both sides of the picture's bottom which I have been unable to fix with the pincushion pot.

I contacted Andy at Ultimarc about these issues and he says it sounds like my monitor has no Vsync signal.  I believe I do have “some” signal as I can make adjustments to lock in the sync at any resolution but the signal is weak or bad.  Changing the resolution just causes all hell to break lose.  Normally I know you have to find a happy medium with your Vhold and 50/60hz pots but nothing works.  I took the Vhold pot out and it tests fine. 5.5K ohms max and multiple readings to confirm it still is adjusting correctly (linearly).

So basically I am going through each inch of the Vertical Deflection circuit to see if I can find anything. The monitor had a cap kit 4 years ago and when the locked in, the picture is appears good (except the bowing which is minimal).  I would say 80% of the solder points on the board look old. Due to this I am just going inch by inch unsoldering, testing, and resoldering. 

Even with no sync at all, you can usually adjust the hold control to make it stay, but you're right it'll be very touchy.  What you're basically doing is adjusting the free-run speed so that it just happens to exactly match that of the source.  This will vary some whenever you chance video modes.

If indeed it works fine on "real" boards, this is almost certainly a problem with your signals, not the monitor itself.  I don't know a ton about the Ultimarc products, but Andy should be able to help in that department.  Make sure that you've actually got everything set up to feed the monitor composite sync.  I don't know that the video amp has any method of doing composite sync generation - it may leave it up to the video source.  While most PCs default to separate sync, the ArcadeVGA may be configured to default to composite, however once the OS loads it just does whatever the drivers tell it to.  Do things sync up during the bootup screens?

[cack01]

On boot and windows it depends. If I shut down with the monitor being in sync with windows then it will boot in sync.  If I sync to a game then shut down it will boot out of sync.  Basically every time I change a resolution I have to play with the "Vhold" pot, and the adjustments need to be to the millimeter to make it stick. Bumping the pot will cause a slow roll.  Andy at Ultimarc said this amount of precision should not be needed and it sounds like I have no Vsync.  There does not seem to be a sweet spot.

Maybe I misspoke on the JAMMA boards.  They worked fine b/c they only use one resolution. I mainly made that statement b/c I didn't want the one word answer of "cap-kit". 

ArcadeVGA sends H-/V-, the amp combines to composite which then goes straight to the monitor.