Motorola ts907 low hv

[timmy]

I already changed the doubler caps to 250 v 180 uf both the same. I checked ac line in at the thermistor with a loss of only 2 volts. I was thinking of replacing the diodes with 1n4007 if I have to. I also had checked for any resistance with the breaker and I also disconnected the diodes and the secondary has 143 vac just what the sams shows. And I don’t want to burn my dvm but I remember I have a ma meter I used to used for cathode current on the rca clones.

[zeno]

One thing bothers me. Go back to @1975 with this set. It comes in
no snd / no raster. Something finally killed it No mater how many
other problems it has, probably many, one thing should bring it back
to just running.
After a quick check to see if the PS is up & running go to the H sweep, maybe
the H out tube is dead. We did not pull a Sams to be sure the voltages were
within 3%. At that point the jug was evaluated ( by eye) & it went from
there. SO IMHO only get the raster back & not worry so much about the
crazy PS voltages. You only need a few voltages to make the H osc & H out run even with lowish B+. You may have bad width but it will give you a raster.

BTW Never blindly trust Sams or the OEM manual !
BTW #2 A good meter is a lifetime investment. Since the 70's I have
had a Hickock ( bench meter) a Beckman & a few flukes. They all still run
& are very hard to accadently get fried. I also got both my sons Flukes
for xmas.
BTW#3 Never blindly trust a tube or CRT checker we NEVER used a tube
checker but had a TOTL B&K for customers & it was a big profit center !

enuf fer now
Zeno
LFOD !

[Username1]

Yes I Agree with Zeno, you need to invest in a good meter. I got me a brand spankin
new Beckman 330 back in the day, Love it, works like a charm. Loved it so much
I got a second a few years ago off ebay for $30. It had calibration stickers on it
from a lab of some kind. Checked it on all scales against my original, & it's Spot On!

The 2V drop across the Thermister is great! At this point you need to partly suspect
your meter on some readings. Also be aware some cheaper meters are not so immune
to AC noise on your DC readings. And DC Amps you have to use probes in series
with what your testing. Clamp is only for AC.

Also be aware that the Horiz Output tubes get a feed from your 385V source, and as
stated above, this could be dragging down your power supply voltages. There are
both Voltage & Current numbers printed on the schematic that can be helpful
in the H Output circuit.

If you have all the stuff in the PS working and have low voltages then you need to look
at excessive current draw somewhere in the set, and that can be dragging down your
voltages.....

This schematic is very smart, Most power supplies will produce it's designed voltage
At some rated Current. Once that current is exceeded the voltage begins to drop.
This is one possibility, and it's for you to find.... That's why there are current readings
at key points on the schematic for this tv......




.

[timmy]

I know there are key points to test but none are listed specifically for ma or amp or what the parameters should be.

[Yamamaya42]

I am also in agreement with what the others are saying, better test equipment is needed.
Especially as many have stated, an oscilloscope, or else you are in risk of just going in circles.

For example, my list of stuff includes.
Fluke 77 Series II Multimeter
Fluke 117 multimeter
Tektronix 7934 oscilloscope
The above is the authority and bedrock of most all my testing.
Extra stuff is.
LCD 1999 3 1/2 BM4070 LCR Meter
LCR-T4 Mega328 Digital Multi Tester
Etekcity Digital Multimeter MSR-A600
Proster Digital Multimeter Mini Multi Tester
Crenova MS8233D Auto-Ranging Digital Multimeter.

This stuff is rather cheap and therefore I'm not afraid to damage it in any kind of risky tests, and they have held up well so far, and even though they are what I deem cheap throw away equipment, they still tend to agree with the calibrated Fluke meters over 97% of the time.

[timmy]

What would cause resistance in the circuit breaker it’s just an on off switch , arcing ?

[Yamamaya42]

Originally Posted by timmy

What would cause resistance in the circuit breaker it’s just an on off switch , arcing ?

The circuit breaker is a common failure point, it's not just an on off switch, it has a thermal element that reacts to current, and causes the breaker to trip when it goes over set point.

carbon on the contacts is the reason for most fails.
If you are seeing large voltage drop across it, then it's clearly bad, you can temp jumper it to see if the voltage problem goes away.

[timmy]

Ok placed the ma meter plugged in started low around 80 ma but as the tubes heated the needle went up steady and quickly and it pinned my meter at 500ma the meter only goes to 500ma so I have a massive load pulling it down.

[Yamamaya42]

Originally Posted by timmy

Ok placed the ma meter plugged in started low around 80 ma but as the tubes heated the needle went up steady and quickly and it pinned my meter at 500ma the meter only goes to 500ma so I have a massive load pulling it down.

SAMS says "580ma" at L54,

So it stands to reason, that once the HV kicks on and the sweeps start up, it will jump over the range of your meter of 500ma, if that's its limit.

[timmy]

My schematic the ma is kind of messed up can’t make out why it says ok so it says 580ma I thought it should be around 380ma. I would think 580 is absolute max

[Yamamaya42]

Originally Posted by timmy

My schematic the ma is kind of messed up can’t make out why it says ok so it says 580ma I thought it should be around 380ma. I would think 580 is absolute max

not exactly, it will be different from set to set, tube to tube, don't be surprised by a difference of 10-15%

[timmy]

Well this ma went up very fast and I would have thought as it approached the 500ma it would have slowed down but it didn’t it was fast. My dvm only goes to 400ua so this meter can’t use

[Yamamaya42]

Originally Posted by timmy

Well this ma went up very fast and I would have thought as it approached the 500ma it would have slowed down but it didn’t it was fast. My dvm only goes to 400ua so this meter can’t use

Avalanche event, horizontal oscillation starts, HV comes up and so does horizontal sweep, there is now boost for the vertical to start, voltage is now optimal at CRT for raster.
All these events in succession cause a rapid uptake in current, this is normal.

[timmy]

Ok makes sense but now it’s anyones guess what’s going on here. I already put in 2 sets of b+ caps the doubler caps.

[timmy]

Well I pulled one tube at a time voltage went up very little or went down alittle at this point this could be either not enough ac for some reason or a cap ceramic or one of the red caps but as of now at least 70% of the red caps are changed already and every one I took out checked perfect unless there’s one I didn’t change may be the bad one.