Hi All,
I am having some trouble with a REL Storm MK1 amp that Is behaving odd! Its a Lateral Mosfet amp, with a pretty basic board using BUZ900/905's.
It powers on, voltages look good and i can initialy hear the 1khz signal fed from my picoscope but it will fade out and then be very tempramental, coming and going but always very quiet.
I have checked the Buz900/905 Mosfets, drivers and replaced the opamps(tl072) all which look good. I have traced the signal out of the preamp onto the powerboard and looks good.. Finally i have reflowed all the solder joints and contact cleaned the pots/switches!
What else should i be looking at, would electros cause this? I cant find a schematic as REL are not forthcoming with these🙁
thanks
Craig
I am having some trouble with a REL Storm MK1 amp that Is behaving odd! Its a Lateral Mosfet amp, with a pretty basic board using BUZ900/905's.
It powers on, voltages look good and i can initialy hear the 1khz signal fed from my picoscope but it will fade out and then be very tempramental, coming and going but always very quiet.
I have checked the Buz900/905 Mosfets, drivers and replaced the opamps(tl072) all which look good. I have traced the signal out of the preamp onto the powerboard and looks good.. Finally i have reflowed all the solder joints and contact cleaned the pots/switches!
What else should i be looking at, would electros cause this? I cant find a schematic as REL are not forthcoming with these🙁
thanks
Craig
I have just recapped it all in case the electro's were bad, all bar the main two power filter ones have been done, didnt have them to hand 5600uF/80v. I have also verified all resistors for drift and match their markings!
The audio seems to cutout when i decrease the frequency of the sine wave input. It also will not get loud again until the caps have completely drained by switching off for a period of time.
I am stumped😕
The audio seems to cutout when i decrease the frequency of the sine wave input. It also will not get loud again until the caps have completely drained by switching off for a period of time.
I am stumped😕
Looks like when powered off the negative power cap doesn't drain down and stays at -63v which would indicate that side isn't correct...
Sorry for the stream on here, first time with a mosfet amp, usually in tubes🙂
Digging further,
I have narrowed it down to the section highlighted in the picture attached.
Its the input to the power board coming from the preamp.
I am going to trace this section out tomorrow but was hoping someone maybe able to give me a hint on this. So if i put my scope on the transitor pin highlighted the sub works! I *think* this is grounding that leg causing the transistor to activate allowing signal to pass, but i cant see what is preventing this to happen without me touching it🙁
I have pulled all the transistors and confirmed they are good with my atlas DCA..
Any help or hints here would be greatly appreciated! Feels like im almost there, been a nit of a learning experience this!🙂
Digging further,
I have narrowed it down to the section highlighted in the picture attached.
Its the input to the power board coming from the preamp.
I am going to trace this section out tomorrow but was hoping someone maybe able to give me a hint on this. So if i put my scope on the transitor pin highlighted the sub works! I *think* this is grounding that leg causing the transistor to activate allowing signal to pass, but i cant see what is preventing this to happen without me touching it🙁
I have pulled all the transistors and confirmed they are good with my atlas DCA..
Any help or hints here would be greatly appreciated! Feels like im almost there, been a nit of a learning experience this!🙂
Attachments
Gonna have to post a schematic. But, that could be a protection circuit that has leaky capacitors, etc.
Yep, understand.
Going to trace out this section as REL wont give out the schematic🙁 cant find one on the web either
Going to trace out this section as REL wont give out the schematic🙁 cant find one on the web either
Err .. um .. pretty sure that's an amp channel -- input differential pair and its CCS, latter being the transistor lead you're probing.
Is your scope probe x10? (Less likely to disrupt circuit being probed 😉)
Cheers
Is your scope probe x10? (Less likely to disrupt circuit being probed 😉)
Cheers
The peculiarity is that the amplifier is located inside the subwoofer housing. It experiences significant thermal and mechanical stress. Violations of rations and cracks in the PCB tracks are possible. A thorough inspection is needed.
I have traced the board out and attached a schematic now! Helped me find the culprit i think too!
In that schematic R6 1.2k was blown although no visable signs, i replaced it with a new 1.2k 0.6w resistor but that let out some more magic smoke so i think it needs to be larger (looks like original is 1w) but i dont have any 1.2k 1w or 2w to hand🙁 would 1k be ok as its providing the ground path for the transistor..
Any thoughts?
In that schematic R6 1.2k was blown although no visable signs, i replaced it with a new 1.2k 0.6w resistor but that let out some more magic smoke so i think it needs to be larger (looks like original is 1w) but i dont have any 1.2k 1w or 2w to hand🙁 would 1k be ok as its providing the ground path for the transistor..
Any thoughts?
Attachments
Isn't R1=170r too low of a value as input impedance? my later strata board (from year 2005 or thereabouts) has a 100K resistor there.
@geoturbo you are right that value is wrong in the schematic, should be 2.7k!
I have found it, i thought it was R6 that was dead but its R3! so 1.2k should have been 10k. Happy Sub now🙂
I can only assume that resistor is close to the maximum wattage and has slowly burnt out. Bigger 10k replaced now!
I have uploaded a schematic if anyone else has issues with the REL Storm Mk1 Power Section.
Thanks for the help all
I have found it, i thought it was R6 that was dead but its R3! so 1.2k should have been 10k. Happy Sub now🙂
I can only assume that resistor is close to the maximum wattage and has slowly burnt out. Bigger 10k replaced now!
I have uploaded a schematic if anyone else has issues with the REL Storm Mk1 Power Section.
Thanks for the help all
Attachments
But .. 2k7 is still too low if it is shunting the input. If it was in series (still ahead of the 2n2 -- C1) it would make a useful contribution as an RFI filter.
You might want to confirm that the LED hasn't acquired a 'soft knee' from the overcurrent. The voltage across 1k2 - R6 sets the operating current for the whole amp, so it's pretty important -- should be in the 2,2 to 2,3V range for a green LED of that era.
Regards
Thanks Craig for all the info and the tracing diagram in this thread. Bought a storm mk1 recently and it suffered very similar problems:
Initially I tried reflowing joints which looked suspect, tested all capacitors however they were fine and the problem persisted.
After finding this thread I desoldered the 10k resister as per your diagram and replaced with a 1w 10k resistor. The resister tested open circuit however it looked visibly fine with no obvious signs of deterioration.
Turned sub on, green light came on and worked beautifully when hooked up to an audio source.
Just wanted to come on here and post some additional detail from my experience in case others face this issue. Thanks again.
- When the sub was switched on it made a short gong sound. Switching on and off would sometimes result in a louder sound than others which was interesting.
- Probing at that particular resistor terminal (the 10k resistor in the power section you traced) while the amp was swithced on I could hear a very faint muffled sound coming through which aligned with the audio which was being played. When probed I could use volume control on the sub.
- Green light on the board (not the switch) was completely off
Initially I tried reflowing joints which looked suspect, tested all capacitors however they were fine and the problem persisted.
After finding this thread I desoldered the 10k resister as per your diagram and replaced with a 1w 10k resistor. The resister tested open circuit however it looked visibly fine with no obvious signs of deterioration.
Turned sub on, green light came on and worked beautifully when hooked up to an audio source.
Just wanted to come on here and post some additional detail from my experience in case others face this issue. Thanks again.
