I recently bought my Pass Aleph P 1.7 back from a friend that I sold it to in 2014 after my position was eliminated. This is a commercial Aleph P, not DIY, with remote and uses the IRF610/9610 FETs. My friend had told me that he was hearing some random noise from the right channel, almost sounding like a dirty pot. This was when listening and not operating the volume control or anything.
When I got it back in January, it has performed flawlessly during this time; no noises, etc. that I detected. Until this weekend, when it appeared that the right channel went out. I took it down on the bench. Examining the internals, nothing appears out of the ordinary. I checked the power supplies and everything seems fine. I do have the service manual pdf.
I then injected a 1khz sine wave into the ch 1 inputs. At the output, the right channel was there, but was 1/3 to 1/2 the amplitude of the left channel. After thinking about it a bit and realizing the attenuator was on the output, I took a look at the amp section outputs for L+ and R+ at the 100R resistors R72 (R) and R42 (L). They looked good and were identical in amplitude. I then took two DMMs and connected the + of each to R42/R72 and the - to the bottom of one of the attenuator resistors in each channel. When operating the volume control, the left channel operated as expected. The right channel however was jumping around in a non-linear fashion at certain points, leading me to believe that one or more of the attenuator relays had gone bad. At this point I think I will replace all 16 of the relays (both channels).
The original relays are Aromat DS2YE-S-DC24V, which appear to be discontinued. I haven't found a datasheet for these, but Panasonic seems to own Aromat now. Any suggested replacements?
If anyone can think of any troubleshooting steps that I may have missed, please let me know. One other thing I may replace are the gain pots, but I haven't identified what they are yet, other than I know they are 2K pots. They seem to be working fine.
Thanks for any thoughts.
When I got it back in January, it has performed flawlessly during this time; no noises, etc. that I detected. Until this weekend, when it appeared that the right channel went out. I took it down on the bench. Examining the internals, nothing appears out of the ordinary. I checked the power supplies and everything seems fine. I do have the service manual pdf.
I then injected a 1khz sine wave into the ch 1 inputs. At the output, the right channel was there, but was 1/3 to 1/2 the amplitude of the left channel. After thinking about it a bit and realizing the attenuator was on the output, I took a look at the amp section outputs for L+ and R+ at the 100R resistors R72 (R) and R42 (L). They looked good and were identical in amplitude. I then took two DMMs and connected the + of each to R42/R72 and the - to the bottom of one of the attenuator resistors in each channel. When operating the volume control, the left channel operated as expected. The right channel however was jumping around in a non-linear fashion at certain points, leading me to believe that one or more of the attenuator relays had gone bad. At this point I think I will replace all 16 of the relays (both channels).
The original relays are Aromat DS2YE-S-DC24V, which appear to be discontinued. I haven't found a datasheet for these, but Panasonic seems to own Aromat now. Any suggested replacements?
If anyone can think of any troubleshooting steps that I may have missed, please let me know. One other thing I may replace are the gain pots, but I haven't identified what they are yet, other than I know they are 2K pots. They seem to be working fine.
Thanks for any thoughts.
Thanks!
If I order some replacement FETs, is it still recommended to use:
IRF610 = FQP4N20
IRF9610 = FQP3P20
If I order some replacement FETs, is it still recommended to use:
IRF610 = FQP4N20
IRF9610 = FQP3P20
why changing them , if they're working?
lazy to check FQ datasheet, but if xconductance is on par, and capacitances are lower, why not
though, I'm using 510 and 9510 without too much thinking - working horses
lazy to check FQ datasheet, but if xconductance is on par, and capacitances are lower, why not
though, I'm using 510 and 9510 without too much thinking - working horses
Thanks. I wasn't planning on changing them, just got a few to have around. Also ordered the Fujitsu relays.
OK. Got the order with the Fujitsu relays and the FQP4N20 and FQP3P20 FETs. I haven't changed anything yet.
In preparation, I decided to look at the signals right at the inputs to the I/O board on the back. The only things I had done at this point are removed the top and bottom of the preamp case for access. I figured I would slowly go thru the volume control steps looking for the R attenuator to flake out as it was when I was ohming it out. The R channel was working fine, but no signal thru the L. WTF!
Today, I started looking at the L channel and the DC bias points were off compared to the R channel. I started ohming out the FETs, and Q16 was showing 2 ohms from S-D. I went ahead and pulled Q16, but before replacing it, I ohmed it out, and everything looked fine, including S-D. So I put it back in, and it appears to be working.
I realize these FETs are 25 years old or so (figuring this preamp was built in 1996 or so). Do they get that flakey after a couple of decades of use?
I assume a production preamp does not use matched parts (no markings on FETs indicative of matching)? I'm hesitant to just button it up like this, wondering when/if it will flake out again. Should I just replace all the preamp FETs (12 of them) in both channels, assuming that same lot is good enough?
Thanks for any advice on this. Flaky stuff drives me crazy 🙂
In preparation, I decided to look at the signals right at the inputs to the I/O board on the back. The only things I had done at this point are removed the top and bottom of the preamp case for access. I figured I would slowly go thru the volume control steps looking for the R attenuator to flake out as it was when I was ohming it out. The R channel was working fine, but no signal thru the L. WTF!
Today, I started looking at the L channel and the DC bias points were off compared to the R channel. I started ohming out the FETs, and Q16 was showing 2 ohms from S-D. I went ahead and pulled Q16, but before replacing it, I ohmed it out, and everything looked fine, including S-D. So I put it back in, and it appears to be working.
I realize these FETs are 25 years old or so (figuring this preamp was built in 1996 or so). Do they get that flakey after a couple of decades of use?
I assume a production preamp does not use matched parts (no markings on FETs indicative of matching)? I'm hesitant to just button it up like this, wondering when/if it will flake out again. Should I just replace all the preamp FETs (12 of them) in both channels, assuming that same lot is good enough?
Thanks for any advice on this. Flaky stuff drives me crazy 🙂
One other thing I found while messing with this: in order to test the muting relays, I ohmed out the connection from the input of the I/O board to the connectors. The L RCA jack was as expected, once the muting relays disengaged, at sub 1 ohm (0.31 and stable). The R RCA out was at 13.x ohms. If I tapped with a finger on the I/O board, it was bouncing around, going up to 70 ohms or greater. After getting the L channel working again, looking with a scope at the outputs, the L channel was rock solid in amplitude. The R channel however reflected what I was seeing on the ohmeter, and was bouncing around in amplitude, sometimes without doing anything, but always when tapping on the I/O board.
These are different relays, but since they are between the board and the back panel, I don't know what they are right now.
Current plan: replace the 12 FETs in the preamp sections, replace the attenuator relays, and replace the back panel relays.
Any thoughts appreciated.
These are different relays, but since they are between the board and the back panel, I don't know what they are right now.
Current plan: replace the 12 FETs in the preamp sections, replace the attenuator relays, and replace the back panel relays.
Any thoughts appreciated.
renew all suspect solder joints first
since you have a scope , try to follow the signal from input and see where exacly it gets wobbly
it's simple circuit, major obstacles are getting your head around physical details/arrangement, and I can't help exactly simply from reason that I never had one in front of me
since you have a scope , try to follow the signal from input and see where exacly it gets wobbly
it's simple circuit, major obstacles are getting your head around physical details/arrangement, and I can't help exactly simply from reason that I never had one in front of me
Thanks. I already followed the signal. It gets wobbly right at the output. It looked fine at the input to the I/O board, after the attenuator, while stepping the attenuator up and down. Good advice on renewing solder joints. Since this is probably 1996 or so vintage, I would guess it is ROHS, so the solder sucks.
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Thanks Wayne. I presume the ones in the PSU are not matched as well, only the amplifier transistors (8 N and 4 P)? For the time being I'll just try to get things working with the parts that were in there. The one IRF610 that went from 2 ohms D-S and was fine once I pulled it bothers me. I hadn't fired up the soldering iron yet when I found that.
I had completely forgotten about working on this once before. When I first got this, #4 input wasn't working. I spoke via email with Kent English who used to do tech support for Pass, and I replaced the driver transistor for that input. That was back in 2013 or so (still had the emails).
I had completely forgotten about working on this once before. When I first got this, #4 input wasn't working. I spoke via email with Kent English who used to do tech support for Pass, and I replaced the driver transistor for that input. That was back in 2013 or so (still had the emails).
Both channels still working today. I got the resistance down on the R channel muting relay to sub 1 ohm after resoldering the relay and the connections from the main board to the I/O board. I tapped on the relay with a screwdriver handle and it dropped below 1 ohm (from around 10 or so). I'll need to replace that relay. I didn't want to pull the back panel and I/O board apart yet so I'll wait until I have a suitable replacement relay.
The ones that are in there are black Omron relays (vs. the Aromat orange relays used for the attenuator), couldn't get clearance to read the part number on the face. The side is marked 2A@30Vdc, and I thought I could read a H-S or S-H below the Omron logo (everything backwards as I was using a thin reflective knife to attempt to see the face of the relay).
Buttoned it up and put it back in the system. Seems to work fine, but I'll need to get back into it later to take care of some of the issues I noted.
The ones that are in there are black Omron relays (vs. the Aromat orange relays used for the attenuator), couldn't get clearance to read the part number on the face. The side is marked 2A@30Vdc, and I thought I could read a H-S or S-H below the Omron logo (everything backwards as I was using a thin reflective knife to attempt to see the face of the relay).
Buttoned it up and put it back in the system. Seems to work fine, but I'll need to get back into it later to take care of some of the issues I noted.
Any recommendation for relays to use to replace the Omrons for the muting/input switching section? I was thinking about using Panasonic TX2-24V (5.8mA coil current) or DS2Y-S-DC24V (8.3mA coil current).
if form factor is the same as Fujitsu ones (I did recommend) , use them
coil current is really not critical
coil current is really not critical
Is the contact current rating an issue? The RY-24W-K are rated at 1.25A vs. the 2A of the others. I could use the RY-24WFZ-K instead? Lower mechanical and electrical life for these however.
no
Aleph P 1.7 isn't welding machine, it is a preamp
you're making typical mistake of overthinking it
been there, done that, zillion times
Aleph P 1.7 isn't welding machine, it is a preamp
you're making typical mistake of overthinking it
been there, done that, zillion times