26k7181 Fuse /HOT Issues

gg3390

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Hello all,

I'm a new member of this forum, and relatively new to monitor repairs, and I'm hoping somebody can help me with an issue I have with my WG monitor above.

I also suspect the monitor is a Zenith version, as there is 2 eht leads to the anode, the VR is an STR30130 and the HOT is marked as TZ1167. Numerous other differences on the board versus the K7000 schematic are evident also.

This monitor (part of an NBA Jam cabinet) worked fine until approx 1 week ago, when the fuse blew.

Unfortunately for me, while trying to repair this machine I made some mistakes along the way - hopefully these have not done any major damage.

Firstly replaced the Fuse - blew immediately again. Then checked the HOT - it was shorted. I ordered a 2sd1398 replacement for this, but the TZ1167 original was plastic, while the 2sd had a metal tab - I did not realise that there would be an issue with ground. Thus, after powering up the 2sd1398 sent out a nice spark and is now dead again.

Also there appears to be shorting between the VR pins, and R103 (2.7R 5W) was open. I tested all other components in the power train and they seem good. While awaiting replacement parts I have tested the rectifier parts, and at this point at the output of the rectifier stage im getting 170V DC (obviously no connection to the VR or HOT and no load on the circuit).

Through the forums here I have checked a number of other parts, D18 , the safety caps across the HOT, and all other parts and they seem to be good. One thing is bothering me though, and this is in reference to both the HOT circuit and the STR VR.

With a new HOT installed I can get a continuity signal from output to ground - This I think is happening through T2, which is showing about 0.8R resistance so would be explained. But with HOTS in Ireland approx €7 a pop its an expensive business being wrong.

Similarly, with STR30130 costing approx €20, I cant afford just to drop them in and see what happens.I have now ordered a replacement STR30130, and a like replacement of the TX1167 (which is as far as ?I can recall a 2sdxxxx but not a 1398). Mica washers behind both VR and HOT will be checked from now on I can assure you.



So (after the essay), I'm wondering if 1) it is possible to run the chassis WITHOUT the VR installed (maybe with the HV shutdown D10 diisconnected to test HOT operation?

2) Can I install the VREG but leave the output pin disconnected while I try to measure the voltage output, which should be about 130V? Will this work and will it cause any damage?

3) Is the resistance in the secondary winding of T2 an issue?

4) is there a specific zenith K7181 schematic?

I've checked D18 etc and caps in the HOT/yoke section of the PCB and these look well. Ive alwo been running the monitor with the degauss disconnected.

The dag wire on the CRT board was broken - butthis happened due to the constant pulling in and out of the chassis.
I havent capped the monitor yet - but actually have most caps replaced. The line output transformer looks good - no goo etc, and was working fine until this unknown incident occurred.

Also wondering how you work safely on this chassis live - to me just discharging the anode is not enough (even though my anode is not working at the minute), but access to the board while connected to both the anode and CRT is akward to say the least.


Thanks in advance for any help you might have - I'm anxious to get this repaired.

Please forgive the essay, and I'd appreciate any advice. Especially anything I can do to save myself blowing VR's and hots. Also, hope I made sense.

Regards
Ger
 
Whew! Okay, let's see what we can do here. It does sound like this is a Zenith K7000A, and hopefully it is being used with an isolation transformer.

Firstly replaced the Fuse - blew immediately again. Then checked the HOT - it was shorted. I ordered a 2sd1398 replacement for this, but the TZ1167 original was plastic, while the 2sd had a metal tab - I did not realise that there would be an issue with ground. Thus, after powering up the 2sd1398 sent out a nice spark and is now dead again.

Yes, you need to put a mica insulator between the HOT and the bracket it is mounted to. Even with the parts replaced properly, if the fuse still blows, you may want to get a 2.5A circuit breaker to attach to the fuse clips during testing, to keep from having to replace fuses all the time. Once it's fixed, you can put the proper fuse in it. I know you're overseas, but Bob Roberts has them ready to go.

Also there appears to be shorting between the VR pins, and R103 (2.7R 5W) was open. I tested all other components in the power train and they seem good. While awaiting replacement parts I have tested the rectifier parts, and at this point at the output of the rectifier stage im getting 170V DC (obviously no connection to the VR or HOT and no load on the circuit).

The VR also needs an insulator between it and the side wall, just in case you are missing one. If you're continuing to blow the VR, check the diodes D19-D22 (near the filter cap) and C38 (big mylar cap near the yoke connector) for shorts.

With a new HOT installed I can get a continuity signal from output to ground - This I think is happening through T2, which is showing about 0.8R resistance so would be explained. But with HOTS in Ireland approx €7 a pop its an expensive business being wrong.

The HOT should be measured with the black lead on the middle leg and the red leads on each of the outer legs. You should get between .400 and .700 if it's good. Measuring between the outer legs will give you about .057 both ways. This is normal, and the HOT is good.

Similarly, with STR30130 costing approx €20, I cant afford just to drop them in and see what happens.I have now ordered a replacement STR30130, and a like replacement of the TX1167 (which is as far as ?I can recall a 2sdxxxx but not a 1398). Mica washers behind both VR and HOT will be checked from now on I can assure you.

The TX1167 is compatible to the 2SD1398, which is commonly shortened to D1398. Both cross reference to an NTE 2302, but the NTE version is usually more expensive over here. I believe the STR30130 crosses to an NTE 1777. You could check the availability over there to see what the price difference are. Over here, I can usually buy each from Bob Roberts for $5 each.

I'm wondering if 1) it is possible to run the chassis WITHOUT the VR installed (maybe with the HV shutdown D10 diisconnected to test HOT operation?

There is a post somewhere around here where a guy found a chassis running that had no VR in it, but I don't think it will work for you - especially since we couldn't figure out how it was doing it.

2) Can I install the VREG but leave the output pin disconnected while I try to measure the voltage output, which should be about 130V? Will this work and will it cause any damage?

Um - maybe? If you really want to try this, I'd think it would be easier to cut the trace off of that pin, test it, then jumper the cut if you get what you like. If you follow the WG K7000 schematic (which is similar enough), you can find the diode at the end of the PS section. Pull the leg out that is opposite the PS section and connect a jumper. Run that to the power tab on a light bulb and connect the bulb's ground tab to ground. You can then power up the chassis and test the PS section without the rest of the monitor connected. If the bulb lights, then your PS section is good. If not - or you blow your fuse or VR, then you know the problem is in the PS section. Dunno if being on 220vac will have any affect on using a bulb for this or not, but I wouldn't think so.

3) Is the resistance in the secondary winding of T2 an issue?

If you are referring to the HOT reading, check my answer above. Usually that reading on the HOT is due to a low-value resistor connecting the two outer legs. If you think T2 is an issue, you'd need a ring tester to properly check the winding.

4) is there a specific zenith K7181 schematic?

I've never seen a schematic specific to the K7000A. The WG K7000 schematic is close enough for troubleshooting. The main differences are in some values (although they are usually compatible to the WG parts) and some of the layouts around the flyback. And of course, they have different flybacks.

The dag wire on the CRT board was broken - but this happened due to the constant pulling in and out of the chassis.

Now, this could be the source of all your problems - if you don't have it connected in some way. The dag wire MUST be connected on this chassis for it to work properly. Not having it connected causes voltage build up and sparking between the chassis and the frame. A lot of times this blows the VR, and sometimes the HOT.

Also wondering how you work safely on this chassis live - to me just discharging the anode is not enough (even though my anode is not working at the minute), but access to the board while connected to both the anode and CRT is akward to say the least.

Well, the way I do it is have a test bench with an isolation transformer and I power it up on the bench with no tube or yoke attached. I put the anode cup inside a glass or plastic jar to keep it away from anything it could spark to (like me). Now I have plenty of room to check voltage or anything else while powering it up. The HV section shouldn't work this way, but if I have a fuse blowing issue, I can do this (with the circuit breaker on the fuse) while I try to inspect and test areas over and over during the repair. Once I have that part fixed, then I can either connect a loose yoke (for load), or put a tube on the bench to connect it to. If you don't have an extra iso transformer to use outside the cab for power, you could build an extension cable from the cab's power connector, then set up a small table near the cab and use the cabs power to test the chassis while you work on it.

Hope some of this helps. I just fixed one of these 25" K7000A's a week or so ago, although it had less problems than you seem to be having...
 
modessitt; The TX1167 is compatible to the 2SD1398 said:
i am fixing a 25k7000 that i cannot find a cross reference to the STR30130 VR that i can buy from mouser(since i live 5 min away, instead of waiting for Bob Roberts in a few more days). any got another cross ref for it besides NTE 1777 cause i can't find on mouser.com?

thanks!
 
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