Hi , I recently bought a Audio Research LS15 tube preamp that is working and sounds very good. It has an issue though. It after it has been on for a while say maybe an hour It automatically shuts off. turning it back on it will work for a little while then shut off again. I bought it knowing this and without knowing how the unit was designed initially thought maybe it was a just a cold solder joint or a crack in a trace maybe a wonky tube socket.
Upon receiving it i discovered that front panel controls are not analog pots and switches but digital and are handled by a 8-bit microcontroller and a couple 8-bit shift registers. In the manual it warns that static discharge could potentially lock up the MCU and require a restart. That got me thinking this is a older unit circa 1998-9ish and maybe the electrolytic caps are out of spec and when it heats up for a while maybe voltage fluctuations are causing the MCU to switch the unit off?
I figure maybe the best course of action is to replace all the electrolytic's and then go from there?
My question is there are no electrolytic's in the audio path just in the PSU and MCU sections , They are all Nichicon VX(M) series caps except the two 470uf (M) 200V main caps which are SMH series snap-in types, all are out of production. Can anyone tell me what series caps would be suitable as modern replacements? They are all temp rated 85c, would it hurt to be looking at 105c? One of them on the underside of the circuit board is a 47uf 250v polar Axial which i don't think is made anymore. Could i just lay a radial type on its side and end the leg over the top? Thanks in advance for any help.
Upon receiving it i discovered that front panel controls are not analog pots and switches but digital and are handled by a 8-bit microcontroller and a couple 8-bit shift registers. In the manual it warns that static discharge could potentially lock up the MCU and require a restart. That got me thinking this is a older unit circa 1998-9ish and maybe the electrolytic caps are out of spec and when it heats up for a while maybe voltage fluctuations are causing the MCU to switch the unit off?
I figure maybe the best course of action is to replace all the electrolytic's and then go from there?
My question is there are no electrolytic's in the audio path just in the PSU and MCU sections , They are all Nichicon VX(M) series caps except the two 470uf (M) 200V main caps which are SMH series snap-in types, all are out of production. Can anyone tell me what series caps would be suitable as modern replacements? They are all temp rated 85c, would it hurt to be looking at 105c? One of them on the underside of the circuit board is a 47uf 250v polar Axial which i don't think is made anymore. Could i just lay a radial type on its side and end the leg over the top? Thanks in advance for any help.
Suggest that you not replace any parts at random, but rather determine the actual problem.
The preamp is in nice shape, and their pcb is very delicate and easily damaged during repairs.
Start by monitoring the AC line voltage, and see if there is a correlation between the shut-downs
and any fluctuations in your AC line voltage. If there are not any, then do the same (carefully) for the
internal regulated high voltages.
Also, does the AC line remain within the acceptable range ( low - high ) at all times?
The preamp is in nice shape, and their pcb is very delicate and easily damaged during repairs.
Start by monitoring the AC line voltage, and see if there is a correlation between the shut-downs
and any fluctuations in your AC line voltage. If there are not any, then do the same (carefully) for the
internal regulated high voltages.
Also, does the AC line remain within the acceptable range ( low - high ) at all times?
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Thanks that's probably the wise approach. AC is pretty stable. Taking a closer look at things now.