Motorola ts907 low hv

[Yamamaya42]

Possible short/ bad part, there are 8 connections to the 190v line, all must be checked, starting with both sides of R215, if 275V is OK, then R215 is suspect, or C2c, or anything that connects to 190v.

But, that is the reason for loss of horizontal oscillator, it needs 190v to work, find why you lost 190v, and it should work again.

[Yamamaya42]

Most likely suspects are, soldering errors, opens or shorts.
or
C61 , R215 ,C2 section c

All other links to that line are via 2k or higher resistors, and would be getting quite hot if shorted.

[timmy]

I had subbed another cap c2 c and the 15k resistor checks 18k so on to the next.

[jr_tech]

Any chance that the 190 and 145 volt supplies are swapped on the schematic? The 15k resistor appears to be too high a value for the current that it must supply. The 190 supply as shown appears to be very weak!

jr

[timmy]

Originally Posted by jr_tech

Any chance that the 190 and 145 volt supplies are swapped on the schematic? The 15k resistor appears to be too high a value for the current that it must supply. The 190 supply as shown appears to be very weak!

jr

And yes that would have made more sense for it to be the other way around since there is only 2 connections and 190 having 8.

[Yamamaya42]

18k is just on the outside edge of tolerance (20%) and very out of 10%.

You may wanna change it with a new 1w 15k one.

Cap cap c2 c subbed with 10uf 350v?

[timmy]

The 190v I never had a problem with that rail until now and the 15k resistor is getting warm like there is a draw and I pulled half the tubes and the cap I subbed was not 350 10 it was bigger voltage and uf

[Yamamaya42]

You will have to track down what the draw is, I would still suggest replacing that 15k with a new 1w one, then follow the 190v line to every place it goes, it has to be something, if it's feeding a resistor that's shorted on the other end, then that will be getting warm. As mentioned, 18k is a tad bit high, you have nothing to lose by replacing it with a same value 15k 1w resistor, it will just be more durable.

[timmy]

I have a 15k 1 watt wire wound I could put in but I know that won’t fix it I will have to trace down all 8 locations that feed 190v.

[Yamamaya42]

Chances are the problematic end also has a resistor on it's side and is getting warm as well, an IR camera would be handy for this such thing.

[Tom9589]

For a number of years as a teenager, I worked on TVs without an oscilloscope. When I finally got one, I couldn't imagine working on TVs without one. Even a cheap one with low bandwidth would make it a lot easier for you to troubleshoot this set. An oscilloscope will tell you whether an oscillator is running and if the waveform is correct. You just can't do that with a DVM. You should be able to find something on eBay. I got my last one from eBay and it was a high end Tektronix for a very good price.

If my house were to catch fire, the Tektronix oscilloscope is the first piece of gear I would remove. 'Nuff said.

[timmy]

Well there are several 2 and 3 watt resistors that normally get hot and up until now I had all tubes out and still a draw and the 275v is around 250v so if one goes down all are going to be low as well. So at this point I’m still thinking it may be a ceramic cap that may have been a problem and now is possibly shorted. How to find I don’t know it means turning this chassis into spaghetti with all clipping and checking and resoldering. Omg what a headache.

[Yamamaya42]

Running raw w/o tubes is not recommended, UNLESS you limit input voltage with a variac.

Reason is, the power supply is non regulated, and dependent on load, the tubes in the set ARE that load, w/o the tubes in the set, the voltage generated can exceed the ratings of the filter electrolytic capacitors and damage them (internal shorts), when you run w/o tubes one must be very careful not to let the bias voltage spike above the rate the capacitors can tolerate, or it can be really bad.

[timmy]

I only tried it for a moment and was watching voltage either way it’s still a disaster.I don’t want it to run to long and stress the fuse wire and or the power transformer or anything else for that matter.just prior to the voltage drop off I think the flyback was buzzing I know they don’t do that but the buzz was from the flyback area.

[Yamamaya42]

Here is how I see this set working ( my take on it ), you have the thermistor R211, cold at 26.5 ohms, as it heats up. It gets lower, they put this in as a protect timer to keep the bias low as the tubes warmed up as not to shock the caps with overvoltage until the heaters were warm enough to load the circuit down enough.
Without tubes in the set, this feature is defeated, and the bias out of X2 at C1 can easily reach over 400v or more and may have damaged the new electrolytic capacitors you have put on there, of course there is no way to know for sure if this is what has happened, but it is possible.