6100 Low B+ voltage

Glitch

Well-known member

Donor 3 years: 2013-2015
Joined
Oct 17, 2011
Messages
3,621
Reaction score
1,496
Location
Anaheim, California
Troubleshooting a 6100 monitor in Black Widow, can use some help. Read 6100 FAQ, numerous threads but can't seem to find a solution.

Symptoms
- Low B+, stuck at ~25VDC. Adjusting pot does not change voltage. Black screen

Checked
Typical Monitor chatter
Neck glow present
Spot Killer not lit
No static felt on screen
Tested deflection board on different 6100 monitor, works fine
All chassis transistors check good
HV transistors good
PCB works (using extension cable in another cabinet)

Replaced:
- Caps
- ZD901/902/903
- Q900/901/902/903/904

Any advice on what to check next? Have (2) HV cages doing the same thing, been swapping parts trying to get a working unit with no luck.
 
Make sure your low voltage section on the deflection board is working, and that you're getting +25V and -25V at the input connector to the cage. If one is missing, you'll get low B+.

Measure the voltages on the deflection board, at the input connector with the cage unplugged, and then also on the cage pins with the cage plugged in. You may have a broken wire or bad connection in the connector. The solder joints also love to crack under the solder joints on the cage connector, but if you have two cages that are doing the same thing, it's more likely the wiring, or the deflection board itself. (Also, if you don't have an LV2000 or LV6100, install one.)
 
Make sure your low voltage section on the deflection board is working, and that you're getting +25V and -25V at the input connector to the cage. If one is missing, you'll get low B+.

Measure the voltages on the deflection board, at the input connector with the cage unplugged, and then also on the cage pins with the cage plugged in. You may have a broken wire or bad connection in the connector. The solder joints also love to crack under the solder joints on the cage, but if you have two cages that are doing the same thing, it's more likely the wiring, or the deflection board itself. (Also, if you don't have an LV2000 or LV6100, install one.)

LV section was replaced for a new LV2000. Installing the deflection on another 6100 monitor works fine.
 
LV section was replaced for a new LV2000. Installing the deflection on another 6100 monitor works fine.

Forgot to mention above, inspected/reflowed headers on HV board to be sure.

Last step would be to install the HV cage into a different monitor to rule out a possible tube issue? Seems unlikely.
 
LV section was replaced for a new LV2000. Installing the deflection on another 6100 monitor works fine.


Ok. Still check the wiring and connector. Make sure you are getting +25V and -25V on the cage traces itself (i.e., after the connector and solder joints on the cage connector, to make sure you're getting power all the way into the cage). If the power to the cage is good, we can go from there, but that's the first thing to confirm.

Also tone out all of traces on the cage, as the traces like to crack around many of the components, in ways you often can't see.

If you're only getting 25V B+, the cage basically isn't working, so it could be almost anything, so start with the power. Test all transistors and diodes (you can do most of them in-circuit). Also, the pots on these go bad very frequently, so it's good to just replace them.

You replaced the Zeners, so that's good, but just make sure you didn't mix up ZD902 and D902, as that's a common error folks make. (You're probably fine, but it doesn't hurt to ask.)

Also, is it the P329 version, with the HV cutoff pot/LED? How is the pot set?
 
Last edited:
gen-mon-flow-low-b-plus99eb042f0f275402.jpg
 
Ok. Still check the wiring and connector. Make sure you are getting +25V and -25V on the cage traces itself (i.e., after the connector and solder joints on the cage connector, to make sure you're getting power all the way into the cage). If the power to the cage is good, we can go from there, but that's the first thing to confirm.

Also tone out all of traces on the cage, as the traces like to crack around many of the components, in ways you often can't see.

If you're only getting 25V B+, the cage basically isn't working, so it could be almost anything, so start with the power. Test all transistors and diodes (you can do most of them in-circuit). Also, the pots on these go bad very frequently, so it's good to just replace them.

You replaced the Zeners, so that's good, but just make sure you didn't mix up ZD902 and not D902, as that's a common error folks make. (You're probably fine, but it doesn't hurt to ask.)

Also, is it the P329 version, with the HV cutoff pot/LED? How is the pot set?

Appreciate the help.

Inspected/did continuity test on traces last night, will try again tonight with a fresh mind. Sometimes that works. Read others possibly mixing up Z vs ZD on the 9xx diodes, so made a point to not make that mistake.

Pot is at the middle position, but voltage does not change when adjusting (I can remove the pot and test with a DMM just to be sure, but other HV cage was doing the same thing). Working on a P329 board at the moment, and cannibalizing a P316 board for a few parts I didn't have on hand, which tested fine. Will do a full rebuild on the P316 once this is solved.
 
Appreciate the help.

Inspected/did continuity test on traces last night, will try again tonight with a fresh mind. Sometimes that works. Read others possibly mixing up Z vs ZD on the 9xx diodes, so made a point to not make that mistake.

Pot is at the middle position, but voltage does not change when adjusting (I can remove the pot and test with a DMM just to be sure, but other HV cage was doing the same thing). Working on a P329 board at the moment, and cannibalizing a P316 board for a few parts I didn't have on hand, which tested fine. Will do a full rebuild on the P316 once this is solved.


If it's a P329 you're trying to fix, you also have the HV cutoff circuit to consider, as there could be issues with that, so it just adds a little more to deal with.

There are two pots on the P329, the HV adjust (in the middle, which will be doing nothing if it's not working, though a bad pot could also be the cause), and the HV cutoff (which is the one on the front edge of the board).

Where is the HV cutoff pot set to, and is the LED lit or not?

Also, another common failure on these is the 555 chip. However if you swap it, be aware that they are oriented differently on the P316 and P329 (pin 1 is in the opposite corner, as the chip is flipped around).
 
If it's a P329 you're trying to fix, you also have the HV cutoff circuit to consider, as there could be issues with that, so it just adds a little more to deal with.

There are two pots on the P329, the HV adjust (in the middle, which will be doing nothing if it's not working, though a bad pot could also be the cause), and the HV cutoff (which is the one on the front edge of the board).

Where is the HV cutoff pot set to, and is the LED lit or not?

Also, another common failure on these is the 555 chip. However if you swap it, be aware that they are oriented differently on the P316 and P329 (pin 1 is in the opposite corner, as the chip is flipped around).

LED on the board isn't lit, have not touched the HV Trip pot since I wasn't 100% sure what it was.

Was going to ask about the 555. I'll try swapping if I can't find anything else that stands out.
 
Have you checked the output of the 555? Start there, trace it up through the base of the HOT. There should be a schematic with DC voltages of all the resistors/diodes/transistors. Once you know you have a good signal going to the HOT, look at these voltages, and see whats out of spec.
 
Update:

Moved to the 316 HV cage and was able to get the monitor up and running with a full rebuild. Picture is shaking, due to low voltage. I'm stuck at +155VDC and cannot get any more voltage out of the adjustment pot.

Replaced
- Q900-904
- Q906
- C901/902/914/922
- ZD900-ZD903
- All Resistors in HV area (R910, 902, 903, 905, 907, 910-912, 926)
- Diode D901-902
- Zener ZD900-902
- 555 Timer

ZD902 still tests fine with the DMM, any other areas that would give me the additional voltage I need? Double-checked D901/D902 as well.
 
Last edited:
Did you replace ZD902? (Sorry, wasn't clear from last post.) If not, replace it anyway. It often gets baked from the nearby power resistors. Also, you can't test a Zener with a DMM. (It will look like a regular diode even if it is bad, as you can't test the reverse-breakdown Zener function with a DMM.)

Also, you don't want to run the cage for long with it in that state. Normally, the pot should be right around the 1-2 o'clock position (where 12:00 is the point closest to the focus block), in order to get 19.5kV, when the cage is operating properly. Anything else indicates something isn't right.

Also, make sure the connector on the cage-mounted transistor on the front (i.e. to the left of the focus block) isn't burned, or showing other signs of heat damage. Many times they are (in which case I remove the connector and solder the wires directly), else I clean the transistor legs with my Dremel wire wheel, as they can get some oxidation built up on them.

Also, it's worth doublechecking all resistor values, to make sure none got mixed up. The silkscreen can be confusing in some areas, and it's easy to misread the resistor numbers in some areas. (Stupid stuff I know, but it's worth sanity checking.)

BTW, if you want to trade your dead cage in for a rebuilt one, PM me.
 
Did you replace ZD902? (Sorry, wasn't clear from last post.) If not, replace it anyway. It often gets baked from the nearby power resistors. Also, you can't test a Zener with a DMM. (It will look like a regular diode even if it is bad, as you can't test the reverse-breakdown Zener function with a DMM.)

Also, you don't want to run the cage for long with it in that state. Normally, the pot should be right around the 1-2 o'clock position (where 12:00 is the point closest to the focus block), in order to get 19.5kV, when the cage is operating properly. Anything else indicates something isn't right.

Also, make sure the connector on the cage-mounted transistor on the front (i.e. to the left of the focus block) isn't burned, or showing other signs of heat damage. Many times they are (in which case I remove the connector and solder the wires directly), else I clean the transistor legs with my Dremel wire wheel, as they can get some oxidation built up on them.

Also, it's worth doublechecking all resistor values, to make sure none got mixed up. The silkscreen can be confusing in some areas, and it's easy to misread the resistor numbers in some areas. (Stupid stuff I know, but it's worth sanity checking.)

BTW, if you want to trade your dead cage in for a rebuilt one, PM me.

ZD900-902 was replaced, good to know on zener testing. I might just replace the zeners again to be 100% sure. I've already changed out the BU406 and checked the socket.

I have the P326 board I can send in, might need a spare neckboard also (going into different build).
 
UPDATE

Issue ended up being another bad ZD902, not sure if I had a bad part or the new one was zapped. Holding steady at 180VDC.

Looks like it'll be handy to keep a few spares on board.
 
Back
Top Bottom