G08 repair logs

p1001

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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.
 
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Wow, that's quite an impressive repair log on G08's!! Thank you for all of the notes on probably one of the toughest monitors of all time to repair!

The G08 is definitely a fustrating monitor!

Here's a question that maybe you could help me on...

I have a bad flyback control on my G08 (it's arcing thru the casing!) What can I use for a repacement flyback or control? I don't know of any replacement flybacks, are there any that could be subbed?
 
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Thanks for your repair notes. I have a stack of these to go thru as well. I have several HV units and fewer deflection boards. I have one HV unit that has a corona discharge all over the outside of it. Looks like something you would see in a display at Spencers Gifts. Not sure what causes that other than a crack in the flyback.
 
Hans;
Thank you for the most excellent repair log. I am going to print this and keep a copy on my bench next to my 6400 wishing stick..... (every time I work on a 6100, I tap it with the stick, hoping that it magically changes into a 6400)...... so far no luck but I know there is one in there, I just have to keep trying.
Jeff
 
Wow, that's quite an impressive repair log on G08's!!

Here's a question that maybe you could help me on...

I have a bad flyback control on my G08 (it's arcing thru the casing!) What can I use for a repacement flyback or control? I don't know of any replacement flybacks, are there any that could be subbed?

I have a HV cage for a g08 with the same issue, all is in very good condition with the exception of the fried pot assembly. I am looking into subbing an old 6100 flyback controller or maybe an old WG assembly. I just have to get the resistance numbers to compare....
Jeff
 
Here's a question that maybe you could help me on...

I have a bad flyback control on my G08 (it's arcing thru the casing!) What can I use for a repacement flyback or control? I don't know of any replacement flybacks, are there any that could be subbed?

You have a bad focus pot? I have one that works fine but the mounting tab is broken. I swapped it for a pot from a scrap HV unit. I hung on to this one in case I ever ran into another bad pot (never did). Figured I'd glue the tab back on or something. Let you have it for $25 shipped.

P1000023.jpg
 
Don't suppose you have a donor IC600 I could buy for my Star Trek Captain's Chair?

While converging my G08; I stupidly resocketted the video connector on the monitor with power applied and lost X deflection. :forehead to palm:
After some debug; I think the X pin shorted to the chassis temporarily.

Some quick debug seems to indicate the X signal is present if I disconnect the clamping board from the main board... IE X shows up at pin1 of the output of the clamping board.
As soon as I connect the clamping board to the main board; the signal disappears indicating there is a shorting path to ground.

I'm looking at the crappy schematics (hard to read due to small nature); and it appears that the X deflection enters IC600 13,14,15 and there are no diodes / transistors in the X path prior to IC600.

I woulda thunk that the 2k2 resistors (R700) would have protected IC600... <sigh>
 
Don't suppose you have a donor IC600 I could buy for my Star Trek Captain's Chair?

While converging my G08; I stupidly resocketted the video connector on the monitor with power applied and lost X deflection. :forehead to palm:
After some debug; I think the X pin shorted to the chassis temporarily.

Some quick debug seems to indicate the X signal is present if I disconnect the clamping board from the main board... IE X shows up at pin1 of the output of the clamping board.
As soon as I connect the clamping board to the main board; the signal disappears indicating there is a shorting path to ground.

I'm looking at the crappy schematics (hard to read due to small nature); and it appears that the X deflection enters IC600 13,14,15 and there are no diodes / transistors in the X path prior to IC600.

I woulda thunk that the 2k2 resistors (R700) would have protected IC600... <sigh>

Let's see if I grasp the problem. With the monitor powered up you plugged in the signal input cable, right? You may have touched pin one (X input) to the frame, grounding it.

Output impedance of the board set is pretty high. I don't see how that could have effected IC600. More than likely there is a semiconductor issue in the X circuit. Did the monitor work before you unplugged and replugged the signal cable?
 
I am having issues with my Space Fury, not getting any blue on the monitor. Any tips on where to start?
 
I am having issues with my Space Fury, not getting any blue on the monitor. Any tips on where to start?

Oscope on the monitor inputs to see if the signal is getting there. Then you can really make a determination if it's a board/wiring or monitor issue.
 
Fixed it, re-seated the chips and she is up and working. Strange guess both boards have issues, i'll re-seat the chips on the 2nd board set and see if that makes a difference as well.

Thanks for the help,

Here is before and after

spf6.jpg



sfblue.jpg

such a cool game.
 
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Let's see if I grasp the problem. With the monitor powered up you plugged in the signal input cable, right? You may have touched pin one (X input) to the frame, grounding it.

Output impedance of the board set is pretty high. I don't see how that could have effected IC600. More than likely there is a semiconductor issue in the X circuit. Did the monitor work before you unplugged and replugged the signal cable?

Correct. Yes; the monitor was working before I converged the monitor.
The problem was simpler than that.
1) the Xpin was longer than the rest; mostly making contact with the frame. Hence the no X ouput.
2) The Pad broke at Pin1 on the deflection board... meaning no xsignal was getting to IC600.

Whew. The monitor is alive again.
Either I'm elephant fingers... or these boards traces are getting worse with age.
Proably both.
 
Got my G08 up and running with a new Bu208a in it. However, after about 5 min, the monitor shuts down. Its related to the spot killer, I can get it to come back on for a little bit when I crank the sensitivity up.. but not for long. I can see the deflection signal on both the x and y pins on the HV board, and when I unplug it and re plug it in it works for a bit. It seems as if the HV is modulated with the vector chatter. Is my IC 900 hosed? (and if it is, does anyone have one?)

Andrew
 
Hi;
Since this is a G08 repair thread, I thought i'd give this a shot here......

Regarding the color tracking on the G08, is it the same initial set-up, R-G-B Drive and Bias fully clockwise, then adjust accordingly?

I just rebuilt a G08 monitor and before I fire it up, I would like to know so I do not fry anything.

Any help would be appreciated.

I searched the FAQ's and did not see anything in the Star Trek manual as well.

Jeff
 
I hit the 5000 max character limit in my original post so I'll start a new log...

Monitor #7
Symptom - Dead
Repair - Visual inspection reveals scorch marks on 600 (vertical) series paddle board and signs of previous repair. I always check the caps for proper values and orientation. Burned deflection parts usually mean blown deflection transistors. I remove, dissasemble, and test deflection block. It has a pair of unmarked transistors in the vertical sink that I can't ID. I swap in two fresh 2N6259's then clean and assemble. Here's a tip...Always pinch the T03 transistor sockets before inserting the 2N6259's for best contact. Visual inspection of deflection board check out fine. I test the 10 deflection transistors in circuit real quick and they're also OK. Reinstall and fire it up. I hear strong deflection and HV crackle. I also hear screaming from the HV unit. A quick check of the 100v board at R306 shows about 100v. A quick wiggle of P900 alters the scream. I know the problem immediately...Cold solder joint. Remove HV unit, give it a cap kit, resolder P900, T900 and the flyback. Reistall HV unit, fire it up and she's working. Somebody had fiddled with R917 and R918 so after a little adjustment I had a beautiful picture. Burn for 3 hours. Done.
 
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