blues deville floating relay

[supertone]

hello,

I'm troubleshooting a blues deville amp, when drive channel is selected all is fine, when the clean channel is selected you can hear the relay switching in a high freq and also the led is flickering.
Measured the voltage on TP31, 32: when drive is selected it reads +14 and -15, when clean is selected the readings are not the expected -14 and +15 but something like +2 and -2

checked the +16 and -16 supply,

please need some advise....

Michel

[mikeboone]

Reflow the solder joints in the +/- 16V circuit, C38/C39 100uF and R85/R86 330 ohm/5 watt.

I have a had a few amps in that series in my shop that were acting up on the switching side and that fixed it.

Also check/reflow the solder joints on the LED that is flickering.

[supertone]

thanx for your reply Mike,

i think the LED is ok, when in drive the led has a steady output but when in clean it has the same freq as the relay.

can the 4560D also be the problem?

[mac1amps]

Actually I would strongly advise taking that suggestion a step further, and resolder as many P.C. board connections as possible, and not JUST the aforementioned areas (AT LEAST on all the jacks & controls). The factory soldering is all "cold", and a complete [and properly done] soldering overhaul will result in an overall sound improvement, as well as more stable operation.

[supertone]

well this means a lot work ahead for me,

isthere anyone who can explain how this channel switching circuit works?

[Dave Curtis, dB AudioTech]

Reflow the solder joints in the +/- 16V circuit, C38/C39 100uF and R85/R86 330 ohm/5 watt.

I have a had a few amps in that series in my shop that were acting up on the switching side and that fixed it.

Also check/reflow the solder joints on the LED that is flickering.

I've fixed a few just by resoldering the LED.

[supertone]

update

just found resistor R62 broken! now looking for a spare one

[52 Bill]

If you're only getting a +/- 2 volt swing at TP31 and TP32, and there is nothing wrong with the +/-16 volt supplies, then there is a problem with the switching circuit.

Check the voltages on all of the pins of the 4560 chip, U3. Make sure the supply voltages on pins 4 and 8 are ok. Check the voltage at pin 2 with the channel switch in both positions. It should be either positive or negative. If the output at pin 1 (TP31) doesn't swing to the full opposite voltage when you switch channels, then try replacing the chip. The output at pin 7 (TP32) is derived from the output at pin 1, so if the output is low on pin 1, it will be low at pin 7.

[supertone]

thanks Bill, this was the kind of answer i was waiting for, just found R62 broken.

Michel

[supertone]

measured voltages at pin 2, TP30, when drive selected 0.0002 vdc, when clean selected 0.9 vdc, changed out the 4560, no effect, fault remains.
output on pin 1 +14 when drive selected and 1.2 vdc (13 vac!)when clean selected.
i'm out of options!

[Enzo]

Does it work OK when the footswitch in connected?

Have you checked out the footswitch jack? There is a cutout contact on the tip inside the jack. if that doesn't make good contact, the circuit will not be complete and the relay can buzz. Power down and measure the desistance across that contact. ANything over half an ohm means the contact needs service.

[52 Bill]

Yes, check the footswitch jack and if you have one check to see if the switching works with the footswitch.

It seems that the "high" voltage (.9vdc) applied to pin 2 isn't high enough to override the voltage applied to pin 3. What is the voltage at pin 3? When checking R62 did you also check R65 and 70? What about CR9?

[supertone]

when in drive voltage on pin 3 is 0.7 vdc and when in clean 0.6 vdc, r70 is ok as are cr9 and r65

[52 Bill]

when in drive voltage on pin 3 is 0.7 vdc and when in clean 0.6 vdc, r70 is ok as are cr9 and r65

What is the voltage at the footswitch line (at the end of R60)?

Did you check C27, CR5 and CR6? If C27 is open or broken off the board the control voltage to the switching circuit will pulse.

[supertone]

between r60 and cr7: dr 0.002 vdc, 0.0075vac. cl 0.9 vdc, 1.24 vac.

strange is that between cr8 and c29 you should expect a minus voltage (like -0.9) but their is nothing