I've been working on G08's for a few days and thought I'd share some of my findings. I plan to add as I go. Hope this helps.
I do have sets of MPSU10/60's available for sale.
Always looking for 2N6259's, IC600's, IC900"s, tinted lens and other G08 parts including chassis and complete monitors.
G08 Repair log:
IMPORTANT NOTE: Most cap kits (including Bob Roberts) include incorrect 50v rated cap for C401. Should be 80v or 100v. I've also seen kits with incorrect output transistors. They should be 2N6259 or equal.
HV unit #1
Symptom - No HV
HV unit has previous work done and new caps. I always check caps for incorrect values. Caps OK. Check for 100v at R306 - OK. Using scope, check for oscillation at base (center leg) of Q901 - OK. Check for oscillation at base (center leg) of Q902 - OK. Check for oscillation at base of Q900 "HOT" transistor - NO oscillation. Working back from Q900 I lose the signal at T900. Cold solder joint. Reflow T900 and we're fixed.
HV unit #2
Symptom - No HV
HV unit has previous work done and new caps. I always check caps for incorrect values. Caps OK. Check for 100v at R306 - only 15v. Unsolder and check Q320, Q321, Q323 - all OK. Decide to remove the red 100v out wire from 100v board and recheck. 100v is OK. Something is pulling too much current in the 100v rail. Only one cap and the flyback connected to the 100v rail. I find C916 is backwards. Replace C916 and we're fixed.
HV unit #3
Symptom - No HV
Check for 100v at R306 and notice all 2 of 3 transistors on 100v board are loose. Remove 100v board and resolder all 3 transistors and repair some loose tracks on board. Can only get 85v at R306. Remove red 100v out wire and recheck. 100v is OK. When HV unit is tested in monitor I get 12kv. I suspect a cold solder joint and reflow the flyback, T900 and P900 plus replace the caps. No change. I probe the circuit with a scope and follow oscillation from IC900 all the way to the HV transformer. All looks good. Check the frequency adjustment pot at R917 - OK. At this point all systems are good but I'm getting low HV and the HV transformer is drawing too much current and browning out the 100v circuit. I assume at this point that I have a short internally in the HV transformer. Set #3 aside for parts.
HV unit #4
Symptom - No HV
100v board is mangled. Replace with a spare 100v board and unit is working. Do preventative maintenance - replace caps and reflow the flyback, T900 and P900. Fixed.
HV unit #5
Symptom - No HV
Check for 100v at R306 - OK. Using scope, check for oscillation at base (center leg) of Q901 - NO oscillation . Check pin 8 if IC 900 - NO oscillation. Usually indicates bad IC900. Remove IC900 and replace with socket and known good IC900. HV unit now working. Do preventative maintenance - replace caps and reflow the flyback, T900 and P900. Fixed.
Monitor #1
Symptom: a)Missing bottom half of deflection, b) all vectors drawn bright white and retrace lines visible.
a)Repair: Since I have left, right and top deflection, problem is narrowed down area of Q603-Q605 and related components. Test and find Q252 (2N3904) on paddle board is shorted. Replace and deflection is restored.
b)Repair; Seen this before. Check voltages supplied to neck board. Missing +55. Replace ZD400 (55v 1/2w) restores +55 and vectors are restored.
Monitor #2
Symptom: Weird, faint, out of place vectors being drawn.
Repair: This one made me think. It appeard most everything was working properly. I had HV, full deflection, vectors being drawn. On a hunch I swapped input protection board and the monitor worked perfectly. Problem was the ground wire from the IP board to J100 was broken inside the insulation. Quick fix.
Monitor #3
Symptom:Burned parts, total mess.
Repair: Start with a cap kit and visual inspection. Notice several burned parts on tied to the positive rail on the 600 side. Tested every transistor plus every discreet component on the +600 side. Replaced Q603, Q601, R636, R253, R251. Replace a couple of heat sinks that were missing. Neck board had so many cold solder joints that components were hanging loose. Reflowed every point on neck board. Time for test... All good but missing bottom half of deflection. Eventually found an almost invisible broken trace on paddle board. Jumped with wire. Retest and all good
Monitor #4
Symptom: Dead
Repair: Replace 2 shorted 2N6259 output transistors and a cap kit restores deflection. No high voltage. Catastrophic failure of HV regulator pcb. Testing and replacement of Q322, Q321, Q323, and R306 restores 100v. No oscillation at pin 8 of IC900. Swap IC900 from parts board restores oscillation, still no HV. Follow signal to Q901 (2N3906) which is installed backwards (!) Flip it and HV is restored. Burned in for an hour, no problems.
Monitor #5
Symptom: Top collapsed, extremely bright vectors
Repair: Replace shorted Q605 2N6259 output transistor, Q603 driver transistor and install cap kit restores full deflection. All vectors drawn at full intensity. No +55 feeding the neck board. Zener diode ZD400 was dead short. Replaced with 1N4757A (51 volt zener) fixed her. Weird failure. Burned in for an hour, no problems.
Monitor #6
Symptom: No deflection, HV shut down
Repair - Monitor is filthy. Cleaning and examination for obvious damage finds horrible cold solder conditions: Reflow all connectors, HV transformer, T900. Install cap kit while I have monitor apart. Quick in circuit check of transistors turns up Q603 and Q703 are bad. Replaced them both with MPSU10's. (Both bad parts are NSDU10! but all other transistors on deflection board are MPSU). Removed and check 2n6259's out of circuit. Replace Q705 that tested as shorted. Fired her up and had partial deflection, missing bottom half.
**While double checking all the connectors I heard a pop and saw smoke. Newly replaced cap C401 blew it's lid. Looks like its part of a voltage doubler circuit. Examination of the cap showed incorrect voltage. Should be 1000uf 80v but was actually a 1000uf 50v. Double checked all my Bob Roberts cap kits and they all had the wrong cap. CHECK YOU KITS. Scrounged a 63v cap for now.
Back to the missing deflection problem. This narrows down the problem to 600 series components tied to the positive +63v rail on the deflection board and Q605 I remove and retest Q601, Q603, Q605 plus the related components in the circuit. All good. Visual examination of the paddle board at P600 reveals missing trace which was repaired:
I also find D251 (1N914 diode) and Q252 (2N3904) to be shorted. Fire it up - all good.
Monitor #7
Symptom - Missing top (X axis) deflection
Repair - Monitor was missing HV unit. Install known good HV, check fuses and for signs of obvious damage. Hook up and it's missing the top half of the screen. This narrows down the problem to 600 series components tied to the positive +63v rail on the deflection board and Q605. Always suspect the 2N6259 driver transistors first. Removed, cleaned and tested driver transistors. All good. Using scope I probe pin 6 of the paddle board output of P600. Signal is present. OK, maybe something was loose or not making contact. I put it all back together and still no top half. Weird. I check connectors and the wiring to the deflection transistors and find that one of the large 1ohm resistors is open (Note: not all G08 monitors have this pair of 1 ohm resistors attached to the heat sink.) I bypass them both and we're fixed.
Deflection board #1
Symptom - Partial deflection and weird sine wave looking vectors. I wiggle the connectors and paddle boards and get glimpses of good vectors. Board is filthy. Had to douse it with simple green and nice it a scrub. Under the grime I find a pristine, unmolested by previous repair board. A quick visual shows obvious cold solder joints on the P600 pins. Reflow all the connectors, install fresh caps and fire it up. Fixed.
Deflection board #2
Symptom - Dead
Visual inspection showed a huge burn mark on the P600 paddle board and signs of previous repair. Checked each component one by one with a DMM and found one of the .16 ohm resistors was open. Replaced it and cleaned up some sloppy solder work. Two of the MPSU60's were replaced with some unidentified transistor so I replaced them. Also did a cap kit while I had it on the bench. Had to clean up several horrible solder jobs from previous repairs. (Did this guy use a blow torch and plumbers solder?) A test of the chassis and I can now hear some deflection but not enough to overcome the HV killer. I probe the top connectors of the paddle boards with the scope and I see deflection on the repaired P600 side but not the P700 side. A closer inspection of the paddle board reveals a minute break in one of the traces. I jump it with a wire and fire it back up. Now I have HV. On the screen I get full vertical (Y) deflection but the horizontal (X) is all bunched to the right 3" of the screen. It's not collapse but rather pushed over. Never seen this before. On a hunch I tried a known good IC600 but no change. I know it's in the 700 series of parts. First I remove all the transistors and test out of circuit. They check out good. I begin to walk through the resistors and diodes in the deflection amp. (Quick tip: compare the components with their counterparts on the other axis. For example measure R720 and compare it with R620.) I finally find that one of the bias resistors to Q702, 180ohm R731, reads low. I pull it and it reads 60ohms and is burned. A quick swap and I fire it up. We're fixed! Burn for 2 hours, next please.
I do have sets of MPSU10/60's available for sale.
Always looking for 2N6259's, IC600's, IC900"s, tinted lens and other G08 parts including chassis and complete monitors.
G08 Repair log:
IMPORTANT NOTE: Most cap kits (including Bob Roberts) include incorrect 50v rated cap for C401. Should be 80v or 100v. I've also seen kits with incorrect output transistors. They should be 2N6259 or equal.
HV unit #1
Symptom - No HV
HV unit has previous work done and new caps. I always check caps for incorrect values. Caps OK. Check for 100v at R306 - OK. Using scope, check for oscillation at base (center leg) of Q901 - OK. Check for oscillation at base (center leg) of Q902 - OK. Check for oscillation at base of Q900 "HOT" transistor - NO oscillation. Working back from Q900 I lose the signal at T900. Cold solder joint. Reflow T900 and we're fixed.
HV unit #2
Symptom - No HV
HV unit has previous work done and new caps. I always check caps for incorrect values. Caps OK. Check for 100v at R306 - only 15v. Unsolder and check Q320, Q321, Q323 - all OK. Decide to remove the red 100v out wire from 100v board and recheck. 100v is OK. Something is pulling too much current in the 100v rail. Only one cap and the flyback connected to the 100v rail. I find C916 is backwards. Replace C916 and we're fixed.
HV unit #3
Symptom - No HV
Check for 100v at R306 and notice all 2 of 3 transistors on 100v board are loose. Remove 100v board and resolder all 3 transistors and repair some loose tracks on board. Can only get 85v at R306. Remove red 100v out wire and recheck. 100v is OK. When HV unit is tested in monitor I get 12kv. I suspect a cold solder joint and reflow the flyback, T900 and P900 plus replace the caps. No change. I probe the circuit with a scope and follow oscillation from IC900 all the way to the HV transformer. All looks good. Check the frequency adjustment pot at R917 - OK. At this point all systems are good but I'm getting low HV and the HV transformer is drawing too much current and browning out the 100v circuit. I assume at this point that I have a short internally in the HV transformer. Set #3 aside for parts.
HV unit #4
Symptom - No HV
100v board is mangled. Replace with a spare 100v board and unit is working. Do preventative maintenance - replace caps and reflow the flyback, T900 and P900. Fixed.
HV unit #5
Symptom - No HV
Check for 100v at R306 - OK. Using scope, check for oscillation at base (center leg) of Q901 - NO oscillation . Check pin 8 if IC 900 - NO oscillation. Usually indicates bad IC900. Remove IC900 and replace with socket and known good IC900. HV unit now working. Do preventative maintenance - replace caps and reflow the flyback, T900 and P900. Fixed.
Monitor #1
Symptom: a)Missing bottom half of deflection, b) all vectors drawn bright white and retrace lines visible.
a)Repair: Since I have left, right and top deflection, problem is narrowed down area of Q603-Q605 and related components. Test and find Q252 (2N3904) on paddle board is shorted. Replace and deflection is restored.
b)Repair; Seen this before. Check voltages supplied to neck board. Missing +55. Replace ZD400 (55v 1/2w) restores +55 and vectors are restored.
Monitor #2
Symptom: Weird, faint, out of place vectors being drawn.
Repair: This one made me think. It appeard most everything was working properly. I had HV, full deflection, vectors being drawn. On a hunch I swapped input protection board and the monitor worked perfectly. Problem was the ground wire from the IP board to J100 was broken inside the insulation. Quick fix.
Monitor #3
Symptom:Burned parts, total mess.
Repair: Start with a cap kit and visual inspection. Notice several burned parts on tied to the positive rail on the 600 side. Tested every transistor plus every discreet component on the +600 side. Replaced Q603, Q601, R636, R253, R251. Replace a couple of heat sinks that were missing. Neck board had so many cold solder joints that components were hanging loose. Reflowed every point on neck board. Time for test... All good but missing bottom half of deflection. Eventually found an almost invisible broken trace on paddle board. Jumped with wire. Retest and all good
Monitor #4
Symptom: Dead
Repair: Replace 2 shorted 2N6259 output transistors and a cap kit restores deflection. No high voltage. Catastrophic failure of HV regulator pcb. Testing and replacement of Q322, Q321, Q323, and R306 restores 100v. No oscillation at pin 8 of IC900. Swap IC900 from parts board restores oscillation, still no HV. Follow signal to Q901 (2N3906) which is installed backwards (!) Flip it and HV is restored. Burned in for an hour, no problems.
Monitor #5
Symptom: Top collapsed, extremely bright vectors
Repair: Replace shorted Q605 2N6259 output transistor, Q603 driver transistor and install cap kit restores full deflection. All vectors drawn at full intensity. No +55 feeding the neck board. Zener diode ZD400 was dead short. Replaced with 1N4757A (51 volt zener) fixed her. Weird failure. Burned in for an hour, no problems.
Monitor #6
Symptom: No deflection, HV shut down
Repair - Monitor is filthy. Cleaning and examination for obvious damage finds horrible cold solder conditions: Reflow all connectors, HV transformer, T900. Install cap kit while I have monitor apart. Quick in circuit check of transistors turns up Q603 and Q703 are bad. Replaced them both with MPSU10's. (Both bad parts are NSDU10! but all other transistors on deflection board are MPSU). Removed and check 2n6259's out of circuit. Replace Q705 that tested as shorted. Fired her up and had partial deflection, missing bottom half.
**While double checking all the connectors I heard a pop and saw smoke. Newly replaced cap C401 blew it's lid. Looks like its part of a voltage doubler circuit. Examination of the cap showed incorrect voltage. Should be 1000uf 80v but was actually a 1000uf 50v. Double checked all my Bob Roberts cap kits and they all had the wrong cap. CHECK YOU KITS. Scrounged a 63v cap for now.
Back to the missing deflection problem. This narrows down the problem to 600 series components tied to the positive +63v rail on the deflection board and Q605 I remove and retest Q601, Q603, Q605 plus the related components in the circuit. All good. Visual examination of the paddle board at P600 reveals missing trace which was repaired:
I also find D251 (1N914 diode) and Q252 (2N3904) to be shorted. Fire it up - all good.
Monitor #7
Symptom - Missing top (X axis) deflection
Repair - Monitor was missing HV unit. Install known good HV, check fuses and for signs of obvious damage. Hook up and it's missing the top half of the screen. This narrows down the problem to 600 series components tied to the positive +63v rail on the deflection board and Q605. Always suspect the 2N6259 driver transistors first. Removed, cleaned and tested driver transistors. All good. Using scope I probe pin 6 of the paddle board output of P600. Signal is present. OK, maybe something was loose or not making contact. I put it all back together and still no top half. Weird. I check connectors and the wiring to the deflection transistors and find that one of the large 1ohm resistors is open (Note: not all G08 monitors have this pair of 1 ohm resistors attached to the heat sink.) I bypass them both and we're fixed.
Deflection board #1
Symptom - Partial deflection and weird sine wave looking vectors. I wiggle the connectors and paddle boards and get glimpses of good vectors. Board is filthy. Had to douse it with simple green and nice it a scrub. Under the grime I find a pristine, unmolested by previous repair board. A quick visual shows obvious cold solder joints on the P600 pins. Reflow all the connectors, install fresh caps and fire it up. Fixed.
Deflection board #2
Symptom - Dead
Visual inspection showed a huge burn mark on the P600 paddle board and signs of previous repair. Checked each component one by one with a DMM and found one of the .16 ohm resistors was open. Replaced it and cleaned up some sloppy solder work. Two of the MPSU60's were replaced with some unidentified transistor so I replaced them. Also did a cap kit while I had it on the bench. Had to clean up several horrible solder jobs from previous repairs. (Did this guy use a blow torch and plumbers solder?) A test of the chassis and I can now hear some deflection but not enough to overcome the HV killer. I probe the top connectors of the paddle boards with the scope and I see deflection on the repaired P600 side but not the P700 side. A closer inspection of the paddle board reveals a minute break in one of the traces. I jump it with a wire and fire it back up. Now I have HV. On the screen I get full vertical (Y) deflection but the horizontal (X) is all bunched to the right 3" of the screen. It's not collapse but rather pushed over. Never seen this before. On a hunch I tried a known good IC600 but no change. I know it's in the 700 series of parts. First I remove all the transistors and test out of circuit. They check out good. I begin to walk through the resistors and diodes in the deflection amp. (Quick tip: compare the components with their counterparts on the other axis. For example measure R720 and compare it with R620.) I finally find that one of the bias resistors to Q702, 180ohm R731, reads low. I pull it and it reads 60ohms and is burned. A quick swap and I fire it up. We're fixed! Burn for 2 hours, next please.
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