Tek 2213a high voltage problem

[Commander Data]

I just bought a non-working Tek 2213A from eBay (it says powers up but
no trace), so I knew I was taking a chance. Symptoms: the unit does
power up, and stays up. Power LED stays on, single sweep LED stays on
when the button is pushed or flashes as I rotate the manual trigger
knob. No buzz, hi-freq noise, no tell tale smell of flyback xformer or
burning stuff. Based on this I think the LV is ok, and powers the
logic board normally. SO chances are the problem is in the HV
circuitry.

Jim Y asked if there is a glow in the CRT, but none at all (in a
darkened room after 1 hours of being left on. Anyone have a clue? I
have no schematic at all, so if anyone in this group can scan that
section of the schematic, it would be appreciated. I have replaced
flybacks in older TVs in the past, so I know how to be careful around
these areas. TIA for your support.

JuliusLR ( at aol dot com )

 

[Jim Yanik]

[email protected] (Commander Data) wrote in

I just bought a non-working Tek 2213A from eBay (it says powers up but
no trace), so I knew I was taking a chance. Symptoms: the unit does
power up, and stays up. Power LED stays on, single sweep LED stays on
when the button is pushed or flashes as I rotate the manual trigger
knob. No buzz, hi-freq noise, no tell tale smell of flyback xformer or
burning stuff. Based on this I think the LV is ok, and powers the
logic board normally. SO chances are the problem is in the HV
circuitry.

Jim Y asked if there is a glow in the CRT, but none at all (in a
darkened room after 1 hours of being left on. Anyone have a clue? I
have no schematic at all, so if anyone in this group can scan that
section of the schematic, it would be appreciated. I have replaced
flybacks in older TVs in the past, so I know how to be careful around
these areas. TIA for your support.

JuliusLR ( at aol dot com )

HV is developed by the same transformer as the low volts supplies.

This instrument's PS functions by rectifying input line AC to DC,then using
a TL594 PWM IC to pre-regulate down to ~43VDC which is used to run a power
oscillator that develops the secondary voltages ,the -2KV cathode supply,
and the +KV anode supply via a HV multiplier.The CRT filament supply also
comes from the power oscillator,it has a separate winding for this.If you
have low voltages,you have the CRT filament supply.You might be able to see
the filament glow from the back of the CRT.It's very possible that the CRT
is dead.I think that if the HV multiplier was bad,the PS would be squealing
or chirping,and there would be no or out-of-spec low voltages.

You could unplug the CRT anode connector and discharge it against the
chassis and find out if you have HV. Be careful,don't let the plug contact
any circuit boards.

Normal troubleshooting is to first check the LV and HV supplies for correct
V,then scope the Horizontal CRT plates for a sweep ramp or large DC
offset(sweep problem),short the CRT vertical plates to see if the trace is
off-screen vertically (vertical problem).Then check the Z-axis for proper
unblanking.The internal CRT grid bias adjustment should be able to turn the
trace on if the CRT is good and LV/HV is working.

 

[Commander Data]

Jim, I've turned to eBay again for the service manual, and it is on
its way. In the mean time thanks for the explanation on how it is
supposed to work. I'll be "poking around" measuring low voltage areas
and try to guess where the problem is, as you suggested. Stay tuned.

Julius

 

[cmdrdata]

Ok, I got my eBay schematic and trace out the low voltages: all LV are
in spec. I can hear a faint but constant high frequency pitch sound,
but don't have a HV probe to check the cathode and anode voltages.
DS870 ( a neon bulb?) that bridges a connection to the one of the
filament connection does not glow.
This is reminiscent of the same problem BobD described in his scope.
Does anyone have a suggestion on how I can measure HV with a DVM (maybe
via hi value resistor divider? if so, what values shoudl I use?) If my
D6 is bad, where can I get a replacement? Thanks in advance for your
help.

 

[Jim Yanik]

Ok, I got my eBay schematic and trace out the low voltages: all LV are
in spec. I can hear a faint but constant high frequency pitch sound,
but don't have a HV probe to check the cathode and anode voltages.
DS870 ( a neon bulb?) that bridges a connection to the one of the
filament connection does not glow.

The neons are for limiting G-K voltages to no more than 120V if the DC
restorer diodes or a HV cap fails. IOW,they should not glow if things are
OK,if there is HV.Maybe just a flash on turn on,but not always on.

You can turn the scope OFF,pull the white CRT anode plug and discharge the
CRT anode lead to chassis and if you get a big fat spark,the HV is probably
good.No spark or weak spark probably means a bad HV multiplier. If so,you
need a parts scope or build your own.Its just a multi-stage ladder-style
diode-cap multiplier.

This is reminiscent of the same problem BobD described in his scope.
Does anyone have a suggestion on how I can measure HV with a DVM (maybe
via hi value resistor divider? if so, what values shoudl I use?) If my
D6 is bad, where can I get a replacement? Thanks in advance for your
help.

You can make a 10:1 HV probe for your DMM by using 4 22.5Mohm(total 90 M)
0.5W 1% metal film precision resistors in series *if your DMM has a 10 M
input Z*(most do);solder them in series,mount in a plastic tube,like an old
tuning tool. I used a 6/32 screw and threaded hex spacer at one end of the
string,so I could use a TEK hook-tip from the *old* P6000 series scope
probes,and a DMM lead and bannana plug on the other end for the DMM pos
input.It all fit in a red tubular hex tuning tool(~3/8" OD/1/4" ID) that we
used for the old 500 series tube scopes.

**BE sure to connect the GROUND lead -BEFORE- the hot lead,to the circuit
under test.** (otherwise,you may zap your meter)

Of course,we had all this stuff on bench stock....


Also,the reason I suggested a service MANUAL is that TEK used to write
these really excellent CIRCUIT DESCRIPTIONS that tell just how the circuits
work,IMO,essential to good troubleshooting.

One very common failure is the focus string of 1/2w resistors increase in
value until they eventually open,and that throws off your focus.You may
need th check them after you verify if your CRT is good or not.(I suspect
not)