Rivera trouble

[Valvehead]

Have a friends Rivera amp here--its a Knucklehead 55 .
Ch. 2 works fine, but ch.1 has signal for about 1 second, then fades down to nothing , very quick. This happens every time i switch channels.

So, i have normal looking voltages at all the pre tubes , heater volts are normal .

Pretty sure i tested every resistor in the pre amp section.

I ran a 400hz test tone through it and here is what i have =

into the fx loop return--all is normal

into V1 , ch2 is normal at grids--nice an loud , switch to ch.1 , signal dies out quick

V2 = tone is very quiet on ch2... both grids---ch.1 fades out quick

V3 = same as V2

V4 - both channels have very loud test tone at pin 7 . nothing at all at pin 2 .

What are the switching parts such as PH102 --and how can i test them...or am i barking up the wrong tree there


schematic

rivera_knucklehead.pdf

[mozwell]

Hi Valvehead
I assume we are talking about the first page of the pdf here.....
There are a lot of optos for the channel switching.
First thing i would check are the power supplies, are they all ok, including the 18V supply for the channel switching optos. Check ALL power supplies are ok when in ch1 and ch2 modes.

i am confused when you say V1, normal signal at grids, but dies out when ch1 is selected, there is no channel switching on v1, so the signal at V1 grids should be the same for both ch1 & ch2.

So the signal path for ch1 is v1a & b in parallel - v2 pins 1, 2, 3 - v3 pin 6, 7, 8 - v4 pins 1, 2, 3 - ch1 volume pot, from here ch1 & ch2 volume pots merge into v4 pin 6, 7, 8

So, put the unit in ch1 mode, inject your signal & follow it through the signal chain above, until you find where it gets lost.

Another thing to check, is when ch1 is selected, measure the DCV across the input to each opto, you should read 1.2 to 2.0VDC across the internal LED, are all of tehse ok ?
D101, PH101, PH104, PH108
PH106 is the ch1 boost opto, it parallels R160 (150k) with R132 (2M2) are both of these resistors ok ?
Does the unit work in ch1 mode with boost ON

Check all the solder joints for any obvious poor joints, heck if you are going over it, touch them all up......

[Valvehead]

OK

Hi Valvehead
I assume we are talking about the first page of the pdf here.....
There are a lot of optos for the channel switching.
First thing i would check are the power supplies, are they all ok, including the 18V supply for the channel switching optos. Check ALL power supplies are ok when in ch1 and ch2 modes.

i am confused when you say V1, normal signal at grids, but dies out when ch1 is selected, there is no channel switching on v1, so the signal at V1 grids should be the same for both ch1 & ch2.

So the signal path for ch1 is v1a & b in parallel - v2 pins 1, 2, 3 - v3 pin 6, 7, 8 - v4 pins 1, 2, 3 - ch1 volume pot, from here ch1 & ch2 volume pots merge into v4 pin 6, 7, 8

So, put the unit in ch1 mode, inject your signal & follow it through the signal chain above, until you find where it gets lost.


QUESTION--I HAVE TO USE A CEL PHONE APP TO SEND TEST TONE--IS THAT GOING TO BE A PROBLEM WHEN I TOUCH THE LEAD TO THE HIGH V OF THE PLATES ?

Another thing to check, is when ch1 is selected, measure the DCV across the input to each opto, you should read 1.2 to 2.0VDC across the internal LED, are all of tehse ok ?

HOW EXACTLY--THERE ARE 2 LEGS--MEASURE FROM EACH LEG TO GND ? OR ACROSS THE 2 LEGS? THE MOST I CAN SEE IS 0.5VDC

D101, PH101, PH104, PH108

VOLTS TO PH101 = 16V/18V
PH104 = 14V/13V

PH108 = 13/15V

AT EACH LEG TO GND.

D101- IS THE RED LED LIGHT FOR CH.1 ---IT DOES NOT WORK.


PH106 is the ch1 boost opto, it parallels R160 (150k) with R132 (2M2) are both of these resistors ok ?

R160 -- CANT FIND IT !
R132 IS NOT INSTALLED IN THIS MODEL



Does the unit work in ch1 mode with boost ON

NOPE

Check all the solder joints for any obvious poor joints, heck if you are going over it, touch them all up......

OK---

[mozwell]

Hi Valvehead
Thanks for the info, that gives us a start.
My guess is it is just in the channel switching.
FIRST, you say D101 doesnt light, with power OFF, measure D101 with your multimeter on diode range, you should get 1 to 2 V one way, and "open" the other way.
With power off, measure the led inputs of PH108 with your multimeter on diode range, do this for PH104 & PH101 also.
Measure R109, is it 390 ohms ?

If D101 is faulty, the channel switching wont work. Replace it & see if this fixes the problem. Check also D102, the ch2 green led.

I should have been more specific......
Power supplies.
Measure TP39 and TP40 to 0V (you can get 0V on the tab of K1 of K3 voltage regulators. Measure on both AC and DC volts ranges.
you shoudl get approx 24VDC, and very small VAC here, if you get a large AVC, more than (say) 2V, i would replace C11 & C12.

All good, lets check the power supply outputs.
TP45 to 0V should be 18VDC with very little ACV ripple
TP43 to 0V should be 18VDC with very little ACV ripple
TP44 to 0V should be -18VDC with very little ACV ripple

All good, then onto the next step, checking the channel switching.
Lets ignore the footswitch, and lets concentrate on the panel switches.
Select ch1, boost off.
Measure DVC on the collector of TR101 or PH108 cathode, this should be 0V
Measure DVC on the collector of TR103 or PH107 cathode, this should be 18V
Select ch2, boost off
Measure DVC on the collector of TR101 or PH108 cathode, this should be 18V
Measure DVC on the collector of TR103 or PH107 cathode, this should be 0V

All good, then onto the next step, checking signal flow through the led's of the optos
Select ch1, boost off.
Measure DVC on PH108 cathode, this should be 0V
Measure DVC on PH104 cathode, this should be a volt or two more than the last measurement
Measure DVC on PH101 cathode, this should be a volt or two more than the last measurement
Measure DVC on D101 cathode, this should be a volt or two more than the last measurement
Measure DVC on D101 anode, this should be a volt or two more than the last measurement
Measure DCV on both sides of R109, one leg should be the same as the last measurement, the other leg shoudl be +18VDC

If all these check ok, then it may be the resistor part of an opto that is not working, we can signal trace through the unit, from the input, to find out which one is not working.

Post results here & we can help you with the next step in the process.
If you find something that doesnt agree, post your results up to that point only, no need to take further measurements.

As enzo & others have often said here, when faultfinding, start at the input, follow the signal through each stage & see where the signal stops or where you dont get what you expect. The fault will be around that area of the circuit.

[Valvehead]

ok--here is some info so far --

ch 1 led tests ok but doesnt light. 1.5v and open
ch2 light works

R109 is 390 ohm

tp39 +28vdc / 0.8vac

tp40 -26vdc / 0.5 vac


tp43 +18vdc
tp44 -18vdc
tp45 +18vdc

CH 1 on =
tr101 coll +14.7vdc
tr103 coll. +12vdc

ch 2 on =
tr101 coll 11vdc
tr103 coll 200mvdc


QUESTIONS =

how exactly should i measure the led in PH101 etc.. its a rectangle shape with 4 legs. so across the length of it ? or just one end ? ive never tested these.

also-- PH107 has a melted side--looks like someone (wasnt me) had a soldering iron against it for a few seconds. Im not sure if thats causing this ? if PH107 was dead --would it cause my problem ?

[mozwell]

Hi Valvehead
Check each optocoupler PH101 etc. Do this with power off.
There should be 2 pins on each side, on one set of pins, you should measure a high resistance, many Meg ohms. On the other side, is the LED, you can check this with your meter on diode range, 1 to 2 V one way, & "open" the other. Keep checking on diode range between combinations of pins until you get the "diode" pins. Most likely these are on the same side & close to each other.

OK
TP39, 40, +/-24V power supplies look ok
TP43, 44, 45 +/-18V power supplies look ok
TR101, 103 look to be your problem, TR101 is not changing in ch1 mode

Once we have checked the optocoupler leds are ok we can go further......

ch1 / 2 switch open
TR102 should be on, its base is pulled high via R145 & R146 to +18V, measure base voltage, is it 0.7V approx, measure collector, is it 0V approx
TR103 should be on, its base is pulled high via R145 & R147 to +18V, measure base voltage, is it 0.7V approx, measure collector, is it 0V approx
TR102 shorts the base of TR101 to 0V, measure TR101 base voltage, it should be 0V and the collector should be >10V

ch1 / 2 switch closed
TR102 should be off, its base is pulled low via R146 to 0V, measure base voltage, is it 0V, measure collector, is it approx 0.6V
TR103 should be off, its base is pulled low via R147 to 0V, measure base voltage, is it 0V approx, measure collector, is it >10V
TR102 no longer shorts the base of TR101 to 0V, and the base of TR101 is now pulled high through R149 & R150. measure TR101 base voltage, it should be 0.6V and the collector should be 0V approx

I would check the value of resistors in this area, also check the soldering (it could just be a bad solder joint).
Check R145 & R149 have 18VDC on one end of them.
5 resistors, & 3 transistors, we could just replace the lot of them

Also, if PH107 was bad, it could cause your problem, but the channel switching transistors are not working correctly, lets fix these first.
When we have checked all the led inputs of the opto couplers PH101 etc, and got the channel switching transistors working ok, we can move on.

[Valvehead]

ok-----

all Optos test good.

some readings from above--

CH 1 ON =
tr102 base 0v coll 15v
tr103 base 7v coll 12v
tr101 base 0v coll 11v

CH2 ON
tr102 base 0,7v coll 0v
tr103 base 0.7v coll 0v
tr101 base 5v coll 15v

R149 does have 18v , i looked and looked for a long time for R145 ---cant find it !!

[mozwell]

TR101 looks to not be operating correctly, i suggest changing it.
Check the 5 resistors around TR101, TR102, TR103, make sure they measure correctly.
Check the soldering of the 3 transistors & the 5 resistors.

[Valvehead]

TR101 looks to not be operating correctly, i suggest changing it.
Check the 5 resistors around TR101, TR102, TR103, make sure they measure correctly.
Check the soldering of the 3 transistors & the 5 resistors.

damn youre good--

it was 101 !!!

thanks you so much man !!!!!!!

amp works perfect now !!

[mozwell]

Valvehead, always happy to help a fellow muso / amp tech.
the other guys here are such a great source of knowledge & help, and i am happy in my small way to make a contribution & help others, whether its posting a sch that i may have, or help in trouble shooting.
As Enzo has said in many posts, first with power off, measure the power devices & transistors, power on through a bulb limiter, check power supplies. Only when these are ok, go any further.
The basic rule of trouble shooting, start at one end, follow the signal through until you dont measure what you expect, and you have found the place of the fault.