Marc Messages: 7 Registered: March 2011 Location: NC
Junior Member
I have pics of the preamp and effects boards from a J595 RV available for upload.
I'd like to add images to this post but I don't have a pic sharing site. How do I go about uploading pics?
I'd be happy to forward them to someone who could upload them....
conductortom Messages: 96 Registered: July 2010 Location: Okla
Member
Pictures look good, but my affects board is different then that one. Is that head a pa head or a guitar head? Was that the right schematics? Thanks Marc and Bart
Tom
Marc Messages: 7 Registered: March 2011 Location: NC
Junior Member
Both are guitar heads, I think. The have two channels; effects and no effects.
the owner only brought the chassis so I'm assuming they are both heads....
Marc Messages: 7 Registered: March 2011 Location: NC
Junior Member
Well, I replaced all the electrolytics on the effects board and found them to be 25% and up out of tolerance and a couple were dead or my fluke just couldn't read them. That replacement shotgun got the reverb working again.
The tremolo as shown in the pics was missing the lamp. the LDR seems to work as it varies with light. I got a #48 lamp and shrink wrapped them all cozy and re-installed the bug. No go on the tremolo. The light end seems to have a varying voltage but there is no action on the ldr end. I tried a known working bug from another kustom and it didn't work either.
I have got over the solder joints touched up a few that looked maybe suspect. I next to nothing about transistor circuit trouble shooting but it seems like all the legs of the transistors have voltages that are roughly close to the schematic.
The schematic I have is very close to the board although the voltages are exact they are pretty close.
Any common fixes that anyone can share?
Thanks,
Marc
The first thing to determine is to see if the lamp is flashing at all. As I recall, the lamp doesn't light up really bright at all, but you should be able to see the light get dimmer and brighter.
If the light doesn't flash, then you need to see if the vibrato LFO (low frequency oscillator) is working. And then see if the driver circuit is getting the fluctuating voltage to the lamp.
Check the dc voltage at the collector of Q310. The schematic shows that it swings from 9-12 volts. You should be able to read the voltage here and see it rise and fall at different rates depending upon where the speed control is set.
If you do have a working LFO, then follow the varying voltage from the collector of Q310 to the top of the intensity control. Then from the wiper of the intensity pot through C315 and R330 to the base of Q309 and on to Q308, etc.
Have you tested the three transistors Q308-Q309-Q310?