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Messages - ryanckelso

#1
Hi All,

Just to let you know, it was the earth connection back to the board.

Some of the cables became disconnected. I sorted this and now it plays!

Heck it gets LOUD!

Thanks for all your help.
#2
To add to the previous post:

I went through the board with the audio probe connected to a separate amp that I know works well.

There is audio at points 5, +CO and even on the white cables connected to the speakers.

So I think the MA board is now working fine - it is amplifying between TR13/14 - TR17/18 and TR19.

I guess the issue is that the speakers are not being driven for some reason to create the sound.

I looked back at an old post to test the AC voltage on the speakers.

Unfortunately there is a 0V reading which I presume is the problem now to create the movement in the cones / generate audio.

All help appreciated!
#3
Hi G1,

I put the 3 electrolytic caps back into the circuit that link to TR24 back into the circuit and the voltages are now:

TR13 Source = 82.4V
TR13 Drain = 106V
TR14 Source = 82.4V
TR14 Drain = 106V

TR17 / TR18 emitter = 106.4V
TR17 / TR18 base = 105.7V
TR17 collector = 63V
TR18 collector = 53V

TR19 base = 62V

+B = 123V
+CO = 62V

TR24 emitter = 107.9V
TR24 base = 107.6V
TR24 collector = 122V

From what I can tell now the circuitry seems to be working better. The voltage from the emitter and collector of TR24 has now dropped, which could be to do with the capacitors being discharged / could be past their life.

TR18 & TR17 collectors are now closer to spec but I feel there should be a larger difference between them.

I tried running through the MA section only and still nothing.

Thanks!

#4
Hi G1,

I removed TR17 & TR19 from the board and tested with diode function. They both give good readings. However as mentioned before TR19:

TR 19 - Collector (Neg) to Emitter (Pos) read 0.59v when in circuit.
OL when out of circuit.

I think that these transistors are fine.

After getting better results changing TR13 I thought I would try the same with TR14.

Again this has helped:

TR13 Source = 90V
TR13 Drain = 116V
TR14 Source = 90V
TR14 Drain = 116V

TR17 / TR18 emitter = 117.7V
TR17 / TR18 base = 117V
TR17 collector = 61V (should be around 80V)
TR18 collector = 75V (should be around 40V)

TR19 base = 74.7V

+B = 124V
+CO = 74V

TR24 emitter = 119V (should be 123V?)
TR24 base = 119V
TR24 collector = 124V

TR16 / 100k = 119V

33 / 160V Cap = 119V


Finally the +CO voltage is closer to centre. But I am still not getting any signal / sound.

The collector voltages on TR17 & 18 are still off and the emitter of TR24 should only be 1V below the +B / collector voltage.

I took TR24 out of the circuit and tested with diode function - all good readings.

Looking at the schematic - I don't have the right voltage hitting the 2 x 33uF /160 Caps - currently 119V whereas should be 123V.

I took all the caps out that are connected to TR24, discharged and took capacitance readings with the DMM.

Value | DMM Reading

4.7uF = 7.9uF
33uF = 39uF
33uF = 46uF

I dont know much about capacitors, so could anyone tell me if these are too far away from their values and could therefore be affecting the voltage readings from TR24?





#5
Hi All,

I replaced TR13 as it failed the diode test.

Original Readings:

TR13 JFET 2SK30
with negative on the gate readings - 1.0v & 0.45v (I believe this should be OL?)
with positive on the gate readings - 0.73v & 0.64v

This has now resulted in the following readings:

TR13 Source = 90V
TR13 Drain = 116V
TR14 Source = 90V
TR14 Drain = 116V
* these could be mis-named, but the voltages are correct in relation to the schematic.

TR17 / TR18 emitter = 117V
TR17 base = 116.5V
TR18 base = 116.5V
TR17 collector = 117V
TR18 collector = 30V

TR19 base = 117V

+B = 124V
+CO = 116V

All in all, the voltage readings are much closer to spec, with drain and source voltages on TR13 / 14 now reading close the the schematic. And the collector of TR18 now reading 30V opposed to 11.7V.

The collector reading on TR17 is still 117V where it should be around 75V when everything is approx 15V down from the schematic.

Do we think TR17 is now the faulty transistor?

Thanks!


#6
Hi g1.

TR21 Base = 115V
TR21 Base / D1 / 10K junction = 115V

Thanks
#7
Hi Enzo,

I retested those points without the limiter:

TR17 base = 116.6V
TR18 base = 116.6V
+B = 123V
+CO = 115V

TR17 Collector = 117
TR18 Collector = 11.7V

Shared point between TR17 & TR18 emitters = 117V.

I think the bases should be about the same - if I am reading the schematic right.

Is there any significance / coincidence that TR17 collector is a 10th of the voltage?

I also found 41V on the circuit after D1 following the 10K 1W resistor connected to the 10/80 cap but then jumps back up to 115V on the 5 rail.

Thanks!
#8
Hi All,

I took a few more readings with the limiter on. Most readings seem about 30V down from the schematic voltage. I've put in brackets what the schematic says at these points.

+B = 108V (137V)

TR24 collector = 107V (137V)
TR24 base = 103V (130V)
TR24 emitter = 103V (136V)

TR16 / 100 resistor = 103V (130V)

TR13 TO TR17 Base = 101V (128V)

TR13 / TR14 / Capacitor = 101V (100V)

TR15 Base = 83V (95V)
TR15 Emitter = 90V (99V)

TR17 / TR18 shared point = 101V

TR17 Collector = 100V (88V)

TR18 Collector = 6V (48V)

All help is appreciated!

Thanks.




#9
Hi Enzo,

I set up the amp to read with the light limiter on.

42W bulb. (it's all I have at the moment). The bulb flashes bright when the amp turns on and then fades to a dim glow.

I took a reading on the leg of the B220k trim pot that goes to D1.
Voltage = 100V

TR24 collector = 106V
TR24 emitter = 101V

+B Voltage = 106V

Perhaps the voltage is down from the limiter?

#10
Hi All,

I thought I would give this another shot with some time on my hands.

AN UPDATE:

G100 410 series 1 UK / Europe version.
Powers up - but no sound through the speakers.
+CO voltage reads 115v when should be 45v.

disconnected PA board from MA and DC. Direct input to MA board with orange wire from schematic - still producing no sound.

Transistor Test undertaken for all - good readings throughout - except:

TR 19 - Collector (Neg) to Emitter (Pos) read 0.59v - unsoldered the joints and retested.
TR19 is okay when out of the circuit.

TR13 JFET 2SK30
with negative on the gate readings - 1.0v & 0.45v (I believe this should be OL?)
with positive on the gate readings - 0.73v & 0.64v

Other Diodes ISI55 & D1 working.

I have built a lightbulb limiter and an audio probe.

I still need help with figuring out why the power supply at +CO is off and where the audio signal is failing.

Many Thanks!



#11
Hi Phatt,

I managed to purchase some crocodile clips and detach the power amp section to a more workable state.

Unfortunately there was a small pop and no there is no guitar signal at all. So something definitely blew.  :'(

I checked the fuses and they are all okay.

I managed to take voltage readings as best I could across the transistors:

Rail 6 voltage = 123V

TR24 = IN 123 / OUT both terminals 119V
TR16 = IN 119V / OUT both terminals 118V (Working)
TR17 = 117V all terminals
TR18 = 117V / 117V / 12V
TR15 = IN 119V / 104V / 97V
TR14 =  IN 117V / 115.5 / 103V
TR13 = All 117V

TR19 = collector 124V
TR20 = collector 124V
TR 21 = collector = 0.59V


I have to deconstruct the MA board even more to get the emitter and base reading for these, so I could only take the metal plate readings, which to my best known are the collectors?

TR22 = 124 in / 115 / 116
TR23 = 116V CV / 0.044V TP / 0.58V

I hope someone can help decipher what the issue is now, and explain it if possible.

Thanks.
#12
Hi all,

I just split the pre and power output stage.

I couldn't hear anything when I set up an input jack to the orange wire to the MA board.

I then re-soldered the orange wire back to point O on the pre-amp and it produces sound at low levels like before.

So I guess it is the power section that has the problem.

Thanks for your help phatt
#13
g1.

Thanks for helping. I thought that 2.1 was indicative of a bad transistor.

After running through again. only TR13 and TR14 read 0.4 across one junction each.

Im going to go back and divide the power and preamp section now.
#14
Hi Phatt,

The CO voltage was definitely 115V before I changed anything on the pot.

I couldnt take voltage readings inside the MA due to the construction when connected to the DC board.

But I took it apart and checked all the transistors in diode mode.

I was getting some interesting results hope you can follow the abbreviations:

R24 = NPN = C-B=0.560 / B-E=0.575 / C(N)-E(P) = OL / C(P)-E(N) = 2.11 = dead

Based on similar reading here are the list of shorted / faulty transistors.

TR19  = Dead - 2SC783
TR20 = NPN = - 2SC783
TR21 = PNP - DEAD - 2SA818
TR16 = dead - 2SA561
TR13 = dead - 2SK30A
TR14 = dead - 2SK30A
TR15 = dead - 2SC1000
TR24 = dead - 2SC484

Here are the remaining working transistors.

TR23 = Good
TR17 = good
TR18 = good
TR22 = Good

Is there anything else I should check on the board? Should replace all the faulty transistors found?

Thanks
#15
Phatt,

I am going to try that test later today.

I thought I would just update everyone.

I took some extra readings. The +CO Voltage is supposed to read +45Vdc according to the service manual.

The reading was +115V, which is way off.

There is a pot in the MA board (VR2) which is a B470k trimmer. I turned this anti-clock wise to the max and now the +CO Voltage = +90Vdc

This has resulted in a louder sound than before, and stopped the surging when powering off. The volume is still too low, and when maxed is a reasonable room level sound.

So I feel that the MA circuit is the culprit.

Any thoughts on what might have failed on the MA board?