Offset problem with TFM-55?

[RichP714]

Hold on. Hold your horses.

Think things are back to normal guys.

I changed caps C301/302 and this boosted the rail.

The old ones were 270pF and I put in 470 pF as it states in the schematics.

maybe you can't always rely on the schematics!!

Let's see. I do some more testing but things seem all ok again (such a small component)

I can't find those componenets (if this goes on much longer I'm going to have to print out the schematics instead of flipping through the pdf) but all's well that ends well.

Don't change too much without checking things periodically

I mailed your other parts out today

[RichP714]

Ah, I found them, bypass caps for those diodes in the over-current protection circuit.

They shouldn't have sagged the rail down at the 470pf called for in the schematic; maybe something close to them was shorting.......

[brit01]

They shouldn't have sagged the rail down at the 470pf called for in the schematic; maybe something close to them was shorting.......

Yep could have been. Think I'll keep the old ones in for now until I know everything else is in place and working.

was listening for about 2 hours last night. Everything sounded sweet. (apart from that background noise from the CT-3)

But I'm sure the bass/lower end is weaker but great clarity and detail especially with the new blue Jeans IC's.
Maybe a burn in time required for all the caps etc.

I'm going to try the Russian paper in oil caps this weekend (if I can get in some time, been neglecting my other half a lot lately)

[brit01]

I tried the paper in oil caps on the RCA board.

woowwww. they sounded beautiful.

BUTTT there was a big grounding problem. I had to attach them by a shortish cable out from the rca board as the caps are large.
It didn't like that

Tried another couple of good quality RTI caps but it's not liking them at all. A grounding problem. It must be because I am wiring them outside of the rca input board.

Have to get hold of some small WIMA's and put these into the circuit.

[brit01]

All new power caps in. All sounding great now.

I've got some cheap polyester 0.47uF coupling caps in right now.

John Broskie (Aikido) sent me some free 0.01 uF polypropolene caps which he recommended highly.
I actually put them in parallel with the 0.47uF polyester and there was an audible improvement. He mentioned experimenting with smaller bypass coupling caps with larger ones.

Hey and guess what? The hissing sound from the CT-3 has been greatly improved. I can turn my tfm-55 gain control up to max and hear no background noise from 12-18 inches away. (and this is only when holographic feature is on)

I'm also experimenting with 30 Hz high pass filters I purchased as with some of my recordings the cones were wobbling a lot with low frequencies.

It has eliminated this problem
At very low volumes the bass is a little affected but nothing to complain about. Actually the speakers sound more detailed and crisp. Maybe the sub sonics coming through were having a side effect on other frequencies.

All that is left are the transistors (for the 30mV dc offset) coming from Rich and the trimming pots for better control.

[snarffydoggy]

All right, I'm glad things are finally coming together

[TNRabbit]

Yes, it's been an awesome journey; now fix the damn thing and listen to it! This thread has grown to epic proportions!

[brit01]

Yes, it's been an awesome journey; now fix the damn thing and listen to it! This thread has grown to epic proportions!

Yep it's pumping out tunes now. Going to run it in this weekend.

But those PIO caps were great. I'm going to fiddle with those next week

[RichP714]

Brit, I'm moving this back onto the thread so my PM box doesn't get full (for some reason I'm pretty anal about keeping it cleaned out).

Anyway:

R226 (on the right channel) is blowing, so the right channel is shot.

First thing to do is make sure the power supply voltages are right.

Next, check all the output transistors on the right channel for a short to chassis. Any pin to chassis, but most especially the center pin (collector)

Next check all pins for a short to each other.

It could be that Q212 you mentioned (it's a driver for the positive polarity) but it could also be something downstream.

Capture.JPG (92.06 KiB) Viewed 1605 times

[brit01]

First thing to do is make sure the power supply voltages are right.

Next, check all the output transistors on the right channel for a short to chassis. Any pin to chassis, but most especially the center pin (collector)

Next check all pins for a short to each other.

Lots of entertainment for the crowds again.
The transistors are matching the left channel except the C/E of Q214.

I should pull the legs out and test it out of circuit??

Also how am I supposed to measure the power supply voltages? Switch on without the R226 in place??

All voltages were perfect before I messed with that coupling cap and something blew. I am kicking myself so hard now. Why didn't I just leave it alone as everything was great.


Ok update.
I lifted the legs of Q214

C -E : no reading either way (there should be a reading one way here yes? This indicates a short?)

E-B : one way (570)

C-B : one way (570)

[RichP714]

First thing to do is make sure the power supply voltages are right.

Next, check all the output transistors on the right channel for a short to chassis. Any pin to chassis, but most especially the center pin (collector)

Next check all pins for a short to each other.

Lots of entertainment for the crowds again.
The transistors are matching the left channel except the B/E of Q214.

I should pull the legs out and test it out of circuit??

Also how am I supposed to measure the power supply voltages? Switch on without the R226 in place??

All voltages were perfect before I messed with that coupling cap and something blew. I am kicking myself so hard now. Why didn't I just leave it alone as everything was great.


Ok update.
I lifted the legs of Q214

C -E : no reading either way (there should be a reading one way here yes? This indicates a short?)

E-B : one way (570)

C-B : one way (570)

Sorry for the no instructions thing; I confused you with the other guy (from Austrailia I think) who'd done this before)

Transistors have 3 pins, emitter, base, collector. Most often collector is in the middle. The emitter/base junction behaves like a diode (conducts in one direction) the base/collector junction behaves like a diode, and the emitter to collector should always be an open (no reading)

Q214 looks good

[brit01]

and the emitter to collector should always be an open (no reading)

Ok so Q214 seems to be ok. No reading either way between E/C .

[brit01]

Am I going to have to lift all the legs of the right output transistors and test each one?

[brit01]

now if the negative 98V cable connecting to D504 had become lose would this cause a big problem?

I was poking around and this cable came off the diode. It was very lose, don't know if it was shorting or I knocked it off now.

Also Q236 readings are much lower than the left channel (same polarities in circuit), but reading only 12/13 compared with 38 on the left channel transistor.

I soldered Q214 back in and the cable connecting D504.

Now still strange is this

Q214 (right)

E/B: 1992 (this should be zero reading like the left channal) other way : 556

[RichP714]

Am I going to have to lift all the legs of the right output transistors and test each one?

NOt to test them for shorts, no