Technical question on K7000

[menace]

Here's my situation: I have 3 chassis

chassis #1 WG K7000 series 538 main board with a P448B neckboard--flyback and IC4 missing--this is the one I'm repairing

Chassis #2 Wg K7000 series 447 main board with P456--new cap kit and flyback condition unknown

chassis #3 Zenith version of the K7000 came with working monitor--board had a hole in it underneath C36 but otherwise complete.  It was shorting across this hole.

What I have done so far:  transferred the new caps from board 2 and put them onto board 1, along with the flyback and IC4 (STR 3123)

Edit:  when I power on, I get no glow in the tube but the large 220 ohm resistor on the side of the chassis heats up like crazy.  What should be my next step to find out where the power is getting diverted?

[Ken Layton]

You made a big mistake as the main boards are different! There are some wiring changes/jumpers on the P538 depending on the voltage regulator installed at IC4. Some of the component values are different on the board.

The P538 board is for either a 25K7191 or 25K7193.

The P447 board is for the 19" and/or 13" tubes with the small neck diameter (22.5mm). Probably for 19K7600 or 19K7900.

Double check for a shorted diode D18 and/or shorted horiz output transistor Q11 (2SD1398 which has an internal diode across collector-emitter).

[menace]

Thanks for the help!  So rather than the STR 3123 as the k7000 spec sheets have, Should I install the STR 30130 that was on the zenith board?

[Ken Layton]

According to the schematic for the 25K7191 (for the P538 board), when you have an STR 30123 installed for IC4, you should have jumpers "JB" (which connects pin 1 to ground) and "JBB" which connects pin 3 to the junction of R103 & R301 (B+). When you have an STR 3123 installed, you should have jumpers "JA" (which connects pin 1 to B+ at R103 & R301) and "JAR" (which connects pin 3 to ground). Both of these IC voltage regulator have the B+ and ground terminals reversed from each other so if you did not change the jumpers for the correct regulator----ka boom! The regulator will be destroyed immediately on power up!

[menace]

I wondered what that smell was --just kidding these old chassis don't smell like anything other than 20 yrs of dust.  Thanks for that info!--Would it be possible to get a copy of those schematics from you--all my information is on the P447 board and the wells gardner service manual .pdf which just lists the different parts required but not specific connections.  Wells gardner was no help either--I'm thinking they don't take us lowly hobbyists very seriously

Ken ,you kick --I'm attempting to get by the auto-censor and should be beaten after I re-read the rules--

oh yeah and another thing that puzzled me was that its a zenith 25" tube with a zenith board and neckboard, yet the tube has 8 pins while the socket is set up for 10 pins?  Can this possibly work or has there been some musical chassis at some point in the distant past?  just curious.  

And believe it or not I'm actually enjoying this!

[Ken Layton]

Yup, it's possible if you don't know the history of the particular chassis you have that *someone* may have 'mixed n matched' boards! Shoot me your email and I can send you the 25K7191 schematics. They are in Visioneer (Scansoft) PAPERPORT . max file format.

[menace]

A big thanks to ken Layton for the schematics--If anyone else wants them I have converted them into a jpg files--this is for the 25" k7191 model--I won't time this message out since I know how hard these are to come by.  I have attached here as well but I'm afraid it might not be big enough to be useful.  we'll see.

[Ken Layton]

Actually it covers two models: the 25K7191 and 25K7193. I did send my Paperport scans of this to Mike's Arcade, but I noticed they haven't been posted yet. You did a great job of combining the two pages. The third page covers the unique parts on this model and has the Wells-Gardner part numbers for them, too. This schematic has been as rare as hen's teeth for quite a while.

[menace]

After a bit of a delay, I'm back at it--got my 500K pot installed as well as 25K for the adjustment board.  I have checked the 30130 chip and it checks good ( I have jumper's JB and JBB installed so that checked)  

I checked Q11 and got 50 ohms across base and emitter (label side up) and infinite ohms between pins 1(base) and 2(collector) and 2 and 3(emitter) so I'm not sure if thats good or not.  power is checked, grounds are solid but nothing--no humming, no neck board light.

so i guess i need to know how to track down a break in the circuit--I'm not thrilled with testing while hot so can you find a problem on a non-energized board?

Also ken, you mentioned d18 as a potential problem--how to check diodes anyways?  I have never had a reason to learn that one.

[Ken Layton]

Did you reverse the polarity of the meter leads when you did the testing of the base to collector? One direction should have infinite resistance and reverse the lead polarity and you should have around 300 ohms (base to collector). If you get infinite resistance both directions then the transistor is bad (open circuit).

[menace]

Yeah B to C = 466 ohms
C to B = infinite
B to E = 50ohms

D18 also checked okay with 440 ohms across the diode (pulled from board) and infinite in the other direction.

I'm really stumped now??

[jerryjanis]

Here's a higher res jpg of the schematic that someone emailed me a while back:

http://jstookey.com/arcade/WG_25k7191/wg_k7191.jpg

[JoeB]

For monitor specs and proper settings:

http://www.wellsgardner.com/wellsgardner31/supportdata/K7000.pdf

[menace]

Good links but if you have a P538 board those specs sheet will lead you solidly astray since you know there are different parts, but you won't know that they go in different than the P447 board--the schematic is a must have for this unit.

Still haven't got mine working--I ordered a new Q11 and IC4 for it since I don't know what a "known good" value for either of these chips are--and they were cheap.

[menace]

Received and installed new IC4 (STR 30123) and Q11 (2SD1398) and sent power and no power  So I followed the troubleshooting guide...AC is good, fuse is closed but no power.  I checked IC4 pin 4 and it was almost 0 (.2V or something) as well as P202 pin 3 on the neckboard (same .2V) .  What part would stop all voltage after the fuse?  

Would a bad flyback give these results?  Oddly enough the board that I got it from has a service note of "no power maybe 200V 560uF--new rectifier diodes/caps 8/23/03"  

Is there a way to test if the flyback is getting any voltage (without a high voltage meter that is  )

[Ken Layton]

Check for voltage on the big white resistor attached to the side of the aluminum chassis (R301 on the schematic). With the monitor powered by an isolation transformer (as usual) put your negative (black) meter lead to chassis ground and the positive meter lead to either one of the resistor terminals. One side of the resistor should show the regulated 123 volts DC. The other terminal should show the raw unregulated DC from diodes which sould be at least 140 volts or more. If there's no voltage on either terminal than R103 is probably open. If there's voltage on R301 but it's way lower than it should be check resistors around C55 & C56 for an open or off value condition.

[menace]

Thanks ken, I checked R301 and there are no volts DC at either pole--Incidently I tested r301 and it reads 180.9 ohms or thereabouts so It's good.  I'm now going to start pulling parts and testing them starting at the power plug and working toward IC4.  .  Please tell me I haven't fried my new IC4 chip  

[Ken Layton]

I don't think you damaged the chip since you have 0 volts at both ends of R301. Work back towards the power plug from R301. I'm thinking you have an open resistor or break in the foil.

[menace]

EUREKA!!  R103 was open so I swapped it with an extra one I stole from the part board it works!  Weird though, because I had checked 103 previously and it read as good--so I must have baked it at some pont during my testing.  Now I can get back to building the cab.

Ken, I just wanted to say thanks very much for offering directions and assistance--that schematic saved my --I'm attempting to get by the auto-censor and should be beaten after I re-read the rules--!!  I can honestly say that without your input, it would still be a dead monitor!

Now, if I could just get that old pizza parlour smell out of it whenever its on, it would be perfect

[Ken Layton]

Yeh, resistors can do that on you sometimes.

Glad your monitor is running and that the schematics helped you out.  

I'm fixing several "basket case" Electrohome monitor boards right now for a local guy here in Olympia, Washington. So far I've got 3 of them up and running good.

[menace]

In the words of Charlie brown AAAARRRRRGGGGHHHH  I'm blowing fuses now and all I did was mount the bloody thing in the case.  I checked C38, C36 and C69.  I get positive results from C38 but inconclusive results from C36 and C69 i.e. they read ok one minute and then nothing the next.  Any ideas are appreciated at this point.  If I have to replace any more parts its an 8-liner chassis for me and this one gets e-bayed for parts

Edit: also checked HOT-->OK

[Ken Layton]

Those 3 caps are the usual blowing fuses suspects, but so is diode D18.

Here's where a good analog multimeter comes in handy. Unsolder and completely remove those caps for out-of-circuit testing with an analog meter. Set the meter to it's highest resistance scale (preferably RX10K). Use alligator clips on the end of the test prods as you don't want your skin resistance to screw up the test results. These caps should make a slight momentary kick of the meter needle. Anything that shows a steady reading on the meter means the cap is leaky and should be replaced.

Does this chassis still blow fuses when it's not mounted? If it only blows fuses when mounted in the game then you may have a cabinet wiring problem or bad isolation transformer.

[menace]

So I replaced C69 (6200pF @1600V) and C336 (3600pF @1600V) and I'm still blowing fuses--D18-d22 check ok as does Q11.  I'm really at my wits end on this thing--any other suggestions would be greatly appreciated.  If no one knows then I'm going to buy another 25" tube and chassis and junk this one.

[Ken Layton]

Try unplugging the degaussing coil. Replace diodes D18 and D15 anyway even if they check good out of the circuit (D18 especially). Try unplugging first the horizontal yoke connector (red and blue) and power up. Then try unplugging the vertical yoke connector and power up.

Sometimes the vertical output ic short circuits on this chassis.

C62 across the 4 power input diodes likes to short circuit so check it, too. Some schematics mistakenly show it as C64.

[menace]

Thanks again Ken--I'll try these and see how it works out.

Edit:

Disconnected de-gauss coil--no change
connected horiz. only then vertical - no change
checked D18 and D15 both check ok--but have no access to new parts  
checked C62 - it reads as open (infinite resistance) I guess thats good??

[menace]

Well I've decide not to junk this thing and have another go at it--(this time, its personal...)  Anyways, when i check resistance from the white power lead to the fuse holder I get a reading of 25 ohms.  So this basically amounts to the thermister (10 ohms) and R104 (15 ohms)--this seems very low or at least a very short circuit path.  Any thoughts?