(Topic ID: 141666)

Rebuilt GTB System 1 power supply - voltage only 17v in HV 42v/60v section


By ForceFlow

4 years ago



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  • 45 posts
  • 11 Pinsiders participating
  • Latest reply 11 days ago by newmantjn
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    #1 4 years ago

    I just rebuilt a Gottlieb System 1 power supply. All the voltages are good with the exception of the 60v and 42v lines. Both the 60 and 42v pins on the power supply give off 17.7vdc. The POT adjustment has no effect.

    The transformer lugs read 74-75 VAC.

    On the power supply, using the negative lead on C6 as ground for the DMM, I tested the voltage on the diodes at the bottom of the board (CR6, CR7), and they read 41.5vac. From the schematic, they appear to be on a 90.4v line.

    So, did I loose that much voltage from the get-go? Or am I testing the voltage incorrectly, and the problem actually exists further down in the circuit?

    20151015204623080.jpg

    All the diodes on the lower third of the board are fresh replacements (cr3, cr4, cr6-cr9, cr21, cr1, and cr2), as well as all the electrolytic pots, the large TO-3 regulator on the back, the POTs, and the header pins. Everything else is original. The regulators do not short to the backplate. The ground mod wire has been done on (on the back, so it's hidden).

    a test fit for the ground wire mod

    #2 4 years ago

    change C7 and also find out why the diode with the 18v drop isnt doing its job. shorted?

    http://www.pinrepair.com/sys1/#power

    Low 60 Volts on the Power Supply.
    An often seen problem with the 60 volt supply (which also gets turned into 42 volts) is low voltage. As in the voltage measures around 20 volts, and transistor Q2 gets *really* hot. After checking the values of the resistors, testing Q2 (TIP31c), and testing the zenor diodes in the H.V. (high voltage) section, no problems are found. The likely cause of this low voltage are bad capacitors C7 (disc .1mfd 200v) and/or capacitor C9/C10 (10mfd 160 volts.)

    #3 4 years ago

    Ok, I replaced C7. The 60vdc pin is unchanged. The 42vdc pin is showing zero vdc.

    The diodes and zener diodes test good.

    The voltages on the banded side of the diodes are now:
    CR7: 97.1vac / 0vdc
    CR6: 32.9vac / 41.7vdc
    CR8 32.9vac / 41.7vdc
    CR9: 97.1vac / 0vdc

    Those seem to be in the ballpark. I'll have to test the transistors and resistors a bit later.

    I couldn't seem to find where C9 and C10 were on the schematic. The only caps I can see in the HV section are C6, C7, and C8. I'm not sure how C9 & C10 fit into the circuit.

    #4 4 years ago

    There are two versions of the system one power supply that I know of.

    The values of C7, C9, and C10 are different between the two is what I've found.

    #5 4 years ago

    On this board:
    C7 was .1uf 50v
    C9 and c10 are 1uf 50v.

    #6 4 years ago

    I've had Q2, Q3, and Q4 all go bad at once before.

    #7 4 years ago

    It looks like the transistors are giving wacky readings with a diode test on each leg.

    Q2 gives 734 & 1915
    Q3 gives 1936 & 773
    Q4 gives 76 & 704.

    It seems odd that all of them would be bad

    On the other hand, just as a sanity check, LIC1 reads 625 & 738, which seems ok.

    A number of resistors seem to don't match the values on the two parts lists I'm looking at. I'll have to go though and read the bands on those next.

    The parts values I'm looking at are from the Sinbad manual and from the 1982 parts catalog--the resistor values are different between the two.

    Originally, this power supply had a "G" in the serial number, so I would guess that I should be looking at the newer parts values found in the parts catalog.

    [edit]: Ok, what I think I'm going to do this weekend is replace Q2, Q3, Q4, and all the HV 1/2W resistors R10-R18. Since it looks like I'll have to replace a few of the resistors anyway, I might as well go ahead and put fresh new ones in for the rest while I'm at it.

    #8 4 years ago

    Ok, I replaced Q2, Q3, and Q4.

    Also R21, R10, R11, R12, R14, R15, R17, and R18.

    I couldn't replace R13 since I didn't have any 33 ohm 1/2w restore on hand, but that one was giving the correct reading.

    The end results weren't much different. The 60v pin is giving 13.3vdc. The 42v pin is giving zero vdc.

    I guess C9 and C10 are up for replacement next.

    #9 4 years ago

    Do you have the insulation spacers in place? I can't tell from your picture, but you need insulators on the screws as well as the transistor tab or you short the transistor to the mount place.

    That board sucks sucks sucks. What a crap design... i think it needs more zener diodes. arghhh. One of the few times i would recommend a repro board.

    #10 4 years ago
    Quoted from barakandl:

    Do you have the insulation spacers in place? I can't tell from your picture, but you need insulators on the screws as well as the transistor tab or you short the transistor to the mount place.
    That board sucks sucks sucks. What a crap design... i think it needs more zener diodes. arghhh. One of the few times i would recommend a repro board.

    I second this. I repair almost anything and I throw these in the trash.

    #11 4 years ago

    I have repaired a few of these, got the parts for not too bad. Crappy design but if they lasted 30 years, rebuilt they should be just fine in Home Use for many years. Of course I think even with my limited design knowledge I could make a better design on perfboard

    #12 4 years ago
    Quoted from barakandl:

    Do you have the insulation spacers in place? I can't tell from your picture, but you need insulators on the screws as well as the transistor tab or you short the transistor to the mount place.

    Yes, the screws on the two transistors have insulators. There are also mica insulators between the backplate and transistors.

    #13 4 years ago

    I've had traces fall off at the spot where Q2 solders to the board. Sometimes that insulating tape falls off leaving a trace unprotected from a short of Q2 when the board gets assembled to the metal plate.

    #14 4 years ago

    The tape is still in place under both transistors.

    #15 4 years ago

    I found a schematic for a newer revision of the power supply, and it has C9 & C10 noted. They were absent on the schematic in the manual for Sinbad. So, now that I have a matching schematic, I can see how C9 and C10 tie into the circuit and could potentially be a problem area.

    I'll probably do the replacement tomorrow.

    #16 4 years ago

    I believe the C9 and C10 on yours will be 1 uf @ 25 volt tantalum capacitors. You might find one of them is shorted or very leaky. Make note of the polarity when removing them.

    #17 4 years ago
    Quoted from KenLayton:

    I believe the C9 and C10 on yours will be 1 uf @ 25 volt tantalum capacitors. You might find one of them is shorted or very leaky. Make note of the polarity when removing them.

    The ones installed are 1uF 50v. The board is marked with a + sign for one of the leads on each one, which matches the + sign on the cap.

    [Edit]: Boy, I sure am glad I did the mod for adding the wires through the board to the regulator on the back. I've already taken the board off the backplate 3 or 4 tines now.

    #18 4 years ago
    Quoted from ForceFlow:

    The ones installed are 1uF 50v. The board is marked with a + sign for one of the leads on each one, which matches the + sign on the cap.
    [Edit]: Boy, I sure am glad I did the mod for adding the wires through the board to the regulator on the back. I've already taken the board off the backplate 3 or 4 tines now.

    There is a cap really poorly marked of polarity. I installed this cap backwards twice and exploded it. It took me really looking close to notice i put the cap in backwards. It was in the high voltage section. You might even be able to find the post i made about it. I think it caused low HV output. i think it was 10uF 63v+

    #19 4 years ago

    I replaced the C9 and C10 caps, but no luck.

    The 60v pin starts put around 17vdc and slowly drops down to 13vdc.

    The 42 pin still reads zero vdc.

    The caps I used were 1uF 40v ceramic, but had no polarity markings.

    https://www.greatplainselectronics.com/proddetail.asp?prod=CCM-1.0uF-50V

    #20 4 years ago

    20151018241412610.jpg

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    #21 4 years ago
    Quoted from ForceFlow:

    I just rebuilt a Gottlieb System 1 power supply. All the voltages are good with the exception of the 60v and 42v lines. Both the 60 and 42v pins on the power supply give off 17.7vdc. The POT adjustment has no effect.
    The transformer lugs read 74-75 VAC.
    On the power supply, using the negative lead on C6 as ground for the DMM, I tested the voltage on the diodes at the bottom of the board (CR6, CR7), and they read 41.5vac. From the schematic, they appear to be on a 90.4v line.
    So, did I loose that much voltage from the get-go? Or am I testing the voltage incorrectly, and the problem actually exists further down in the circuit?
    20151015204623080.jpg
    All the diodes on the lower third of the board are fresh replacements (cr3, cr4, cr6-cr9, cr21, cr1, and cr2), as well as all the electrolytic pots, the large TO-3 regulator on the back, the POTs, and the header pins. Everything else is original. The regulators do not short to the backplate. The ground mod wire has been done on (on the back, so it's hidden).
    a test fit for the ground wire mod

    You are trying to measure AC using a DC ground
    Measuring across the banded end of cr6 to the banded end of cr8 you should get 70vac or non banded cr7 to non banded cr9
    Banded end of cr7 and cr 9 should read 90 VDC with the negative lead now going to C6
    Banded end of cr6 and cr 8 and non banded ends of cr7 and cr9 are your transformer input voltage of 70 vac

    Quoted from wiredoug:

    change C7 and also find out why the diode with the 18v drop isnt doing its job. shorted?
    http://www.pinrepair.com/sys1/#power
    Low 60 Volts on the Power Supply.
    An often seen problem with the 60 volt supply (which also gets turned into 42 volts) is low voltage. As in the voltage measures around 20 volts, and transistor Q2 gets *really* hot. After checking the values of the resistors, testing Q2 (TIP31c), and testing the zenor diodes in the H.V. (high voltage) section, no problems are found. The likely cause of this low voltage are bad capacitors C7 (disc .1mfd 200v) and/or capacitor C9/C10 (10mfd 160 volts.)

    CR12 drops the voltage 18 volts, 17.7v minus 18 is about 0, A shorted 18 volt zenor diode would result in the 42 volt line to be the same as the 60 volt line, in this case be 17.7
    C7 is a high frequency bypass capacitor. If open no problem, if shorted the base voltage for Q4 will be driven to 0, causing a very extremely hot Q4
    Just for fun try removing c7 c9 and c10 completely from the circuit, As these are only HF bypass filter you can safely test the circuit without them being installed

    If you could provide the voltages for each leg of the transistors, this could easily be fixed. First you have to make sure your input voltages are correct and you bridge rectifier setup is working correctly putting out 90VDC
    Measure the voltage across your Zenor Diodes, a 12 volt zenor will measure 12 volts measure across it

    As far as design, I think it is good, but a little more difficult to work on , on the five volt section this power supply has a over protection circuit that is excellent. if the power transistor shorts or the output voltage goes above 5.6 volts a zenor diode conducts feeding the gate of an SCR shutting down the power supply saving all your chips on the MPU.

    #22 4 years ago
    Quoted from gregfilek:

    A shorted 18 volt zenor diode would result in the 42 volt line to be the same as the 60 volt line, in this case be 17.7

    yes .. and as he said ( probably wrongly) in the post at the top ...

    Quoted from ForceFlow:

    Both the 60 and 42v pins on the power supply give off 17.7vdc.

    #23 4 years ago

    I am too lazy to read everything.....

    In Case someone did not already mentioned this..

    To test voltage properly on a Gottlieb System 1, Everything must be plugged into power supply or you won't get correct readings.

    #24 4 years ago
    Quoted from gregfilek:

    You are trying to measure AC using a DC ground
    Measuring across the banded end of cr6 to the banded end of cr8 you should get 70vac or non banded cr7 to non banded cr9
    Banded end of cr7 and cr 9 should read 90 VDC with the negative lead now going to C6
    Banded end of cr6 and cr 8 and non banded ends of cr7 and cr9 are your transformer input voltage of 70 vac

    banded CR6 to banded CR8 = 73.5vac
    banded CR7 to banded CR9 (neg lead on CR7) = it read about 40vac the first time I tested. However, when tried a second time to verify the exact voltage, it then read zero.

    CR6-CR9 appear to all test good with the diode DMM test.

    Quoted from gregfilek:

    CR12 drops the voltage 18 volts, 17.7v minus 18 is about 0, A shorted 18 volt zenor diode would result in the 42 volt line to be the same as the 60 volt line, in this case be 17.7

    Thanks, that makes sense. However, at the moment, it doesn't appear to be shorted. I may have been mistaken in the OP about the 60v and 42v lines reading the same the first time around. Too many numbers floating around in my head, maybe.

    Quoted from maddog14:

    I am too lazy to read everything.....
    In Case someone did not already mentioned this..
    To test voltage properly on a Gottlieb System 1, Everything must be plugged into power supply or you won't get correct readings.

    Without a load attached, you can still test for a ballpark voltage within a couple volts of the expected voltage. I've done it on other games and have seen videos of other people do it. It's not going to be off by 50v like I'm seeing here.

    #25 4 years ago

    I replaced CR6, CR7, CR8, and CR9 again. No change.

    banded CR6 & CR8 = 73vac
    banded CR7 & CR9 = 0vac

    With a continuity test:
    The banded sides of CR7 and CR9 are connected.
    Pin 7 connects to unbanded side of CR9.
    Pin 6 connects to unbanded side of CR7.

    #26 4 years ago

    I replaced CR10, but there was no change.

    CR7/CR9 still reads zero.

    The 60v and 42v pins both read zero.

    I'm not understanding what the issue is here.

    #27 4 years ago

    cr7-cr9_voltage_test.jpg

    cr6-cr8_voltage_test.jpg

    #28 4 years ago

    Those four diodes are forming a full wave bridge rectifier. It is easier to comprehend what is going on when they are show drawn in the diamond shape on a schematic. Two junctions of the bridge will be the AC inputs. One will be negative (ground) the other will be the positive voltage.

    Also the high voltage has an isolated return from the rest of it of the board. Keep that in mind when you are probing things.

    #29 4 years ago

    I've always had trouble with understanding how to properly probe AC power.

    Because the HV area has a separate ground, I was using the negative side of C6 to probe for VDC on the 60vdc/42dvc pins, since I saw that indicated somewhere. Should I also use the negative lead of C6 as ground if I want to probe the banded sides of CR7 and CR9?

    As a sanity check, I tested a different power supply that had not been rebuilt, and it was giving all the proper voltages (only the A2J1 connector with input power was connected to the power supply).

    #30 4 years ago

    seriouslee.jpg
    Plug everything in to test the voltage output of the power supply.

    I know this first hand. I own and have owned and restored a bunch of System 1's. I have more spare system 1 parts laying around than Forrest Gump has chocolates in his box. ( Which really doesn't mean much, but I just wanted to say it)

    #31 4 years ago
    Quoted from maddog14:

    seriouslee.jpg
    Plug everything in to test the voltage output of the power supply.
    I know this first hand. I own and have owned and restored a bunch of System 1's. I have more spare system 1 parts laying around than Forrest Gump has chocolates in his box. ( Which really doesn't mean much, but I just wanted to say it)

    It's not necessary in this case. You can still test for output voltages on a System 1 power supply. Besides, this is the method I prefer to use so as to avoid causing damage on other boards if voltages are shorting or incorrect. That way, I can fix smaller problems before they become bigger ones.

    In any case, I pulled another system 1 power supply out of my parts stash, tested it, and got reasonably good voltages out of it. Then I tore it down and rebuilt it. And success--all the output voltages were as expected.

    I'm still not sure why the earlier board I rebuilt is still having problems, though.

    20151019222704804.jpg
    20151021193912602.jpg

    1 month later
    #32 4 years ago

    wow nice work, how do you get those old cap's off, they seem to be glued to the board with some industrial nasa kind of shit.. ?

    #33 4 years ago
    Quoted from chrisnack:

    wow nice work, how do you get those old cap's off, they seem to be glued to the board with some industrial nasa kind of shit.. ?

    Make sure you get all the solder with a vacuum pump, clip the leads (for the axial caps), then wiggle the caps loose.

    [Edit]: also, I wrote up a guide on pinwiki for rebuilding the power supply, which might help a bit:

    http://pinwiki.com/wiki/index.php?title=Gottlieb_System_1#Recommended_Power_Supply_Updates_.26_Repairs

    2 months later
    #34 4 years ago

    I think I may have found where the problem was on the power supply where the HV section wasn't working.

    I was clearing my worktable of projects, and I happened to notice that the C8 cap was bulging. I compared it to a working power supply that I rebuilt and noticed that C8 was backwards--the polarity was reversed.

    In my defense, C8 , C9, and C10 are all packed in so closely together that it's hard to tell which component the + marking is actually for.

    I haven't actually replaced C8 yet, but it sure seems like this may be the source of the original problem.

    4 years later
    #35 13 days ago

    I'm having this exact problem. Was c8 the fix??

    #36 13 days ago
    Quoted from newmantjn:

    I'm having this exact problem. Was c8 the fix??

    No, it's still on my workbench after all this time. I put it aside since the other rebuilt one was working, and never circled back around to this one.

    #37 13 days ago

    OK, I have the exact same thing. I had a power supply that was more or less OK - needed new caps etc., So I put in the new parts per pinwiki and now I have this mess. A hot Q2 and low 60/42. The thing is, this is my second one like this. I finally punted on the last one and stripped off the capacitors and put them into another power supply (that oh, by the way) is working fine. I double checked the cap orientation to the working PS all that. I just can't figure this out for the life of me.

    Yes, I know, buy a rottendawg or whatever. I just really want to fix these and maybe learn something in the process. You don't learn anything firing new parts into a machine.

    #38 13 days ago

    I get it--most of the time I prefer to repair rather than replace as well.

    I've done a few other power supply rebuilds that worked fine, but for some reason, this particular one didn't seem to want to work.

    #39 13 days ago

    make sure you put the caps in the right polarity. The PCB markings with + is kind of confusing for one of them and easily goes in backwards. Results in low HV and if you leave it powered on long enough the cap heats up and explodes. I know for XP. =O

    Comparing to a working board was how I noticed a cap was in backwards. Looking at the pcb printing it was easy to see how that happened.

    #40 13 days ago

    Mica insulators under high voltage transistor?
    Metal screw going through the transistor and heatsink - electrically tying them together?

    #41 12 days ago
    Quoted from barakandl:

    Comparing to a working board was how I noticed a cap was in backwards. Looking at the pcb printing it was easy to see how that happened.

    I did exactly that below. I have a bottom board out of another game, so I'm using that as a poor mans test bench.

    The first two pictures are of a properly working power supply that I rebuilt. The last one is the one that is not working correctly. I double checked all the caps and they seem to all be orientated correctly. If you notice something please let me know. Also, I added a new insulator under Q2. Also, in case it isn't clear, I'm on the 42v output in the first picture and the 60v output in the last one. I should have done 60v for both.

    I'm stumped. Q2 got so hot I damn near burned my fingers on it.

    IMG_3138 (resized).JPGIMG_3139 (resized).JPGIMG_3140 (resized).JPG

    #42 12 days ago
    Quoted from G-P-E:

    Mica insulators under high voltage transistor?
    Metal screw going through the transistor and heatsink - electrically tying them together?

    Hi Ed;
    Thanks for writing. Please look at the pictures above, I'm actually on a bench, so there is no short to the plate possible.

    Note, however, that I did order a few mica insulators from you a few days ago. Also, I thing I'm going with nylon screws on some of these, as I don't have all the old pass through insulators.

    #43 12 days ago
    Quoted from newmantjn:

    as I don't have all the old pass through insulators.

    They're called shoulder washers--that should help you find them.

    #44 11 days ago

    AAvid part number 7721-7PPS or 7721-7PPSG.
    Use with #4 hardware.

    #45 11 days ago

    OK, I had a dumbass attack.

    I was thinking - what changed? Go back and double check everything.

    Took another look at c8. It was installed correctly, but slightly bulging. Further examination showed it was 470uf, not 47. I put in a 47uf cap and it seems to be happy now.

    Just need a few shoulder washers.

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