Avalon vt-737sp

[TheseGoToEleven]

Yup definitely not like mine. K will rest in a bit again. But I think I couldn’t get any voltages from any of those T points

If by test points you mean the wired outputs of the vertical board, then do the push buttons light up when pressed in? This is guessing -- but I imagine the yellow wire is +12V DC supply to that board, black wire is 0V, purple for high pass filter in/out, and orange for high gain. Red and blue are probably the other two buttons for phantom and phase.

 

[Jdm5149]

Yes. All buttons light up. Just no signal is passing thru. With mic plugged in or instrument

 

[Jdm5149]

Issue must be on the i/o board. I read an old post about it being the relays. Just wondered where they were and how to test

 

[TheseGoToEleven]

Issue must be on the i/o board. I read an old post about it being the relays. Just wondered where they were and how to test

You probably know this, but just in case -- the VU meter won't show input signal level, just output or compression. To trace the input signal and see where it stops, I used an oscilloscope. If you keep all the buttons pushed out (lights off) then the signal path will be simpler to trace since less circuitry is involved (no compressor, eq, high pass filter, etc.)

I'd suggest using a mic and checking that the audio signal at least makes it past the input transformer and through the gain pot at pads #14 and #13. There are no relays involved yet at that point. Then see if the signal is still there at T9 and T10.

I think I will add some more annotation to the couple of photos that I have. I stopped part way through but some of the relays and other controls are easy enough to identify without having a unit on hand.

The extra caps and other non-original parts might be more of an initial concern, along with power supply. Make sure that stuff is good. Pucho has probably forgotten more about 737's than I'll ever know.

 

[pucho812]

I was wondering that too. Some kind of mod? They were not there at all on the unit I worked on.

They are connected to the same spots the white Avalon film caps would be.
So either they are replacing the Avalon film caps or they have caps in parallel for some odd reason

 

[Jdm5149]

Thanks for all your help. I will continue tomorrow. I know from serial number it’s an older unit.

 

[pucho812]

Thanks for all your help. I will continue tomorrow. I know from serial number it’s an older unit.

old unit or not, the orange and the yellow caps are non standard.
Are they on the unit you are working on?


Whenever we did testing on 737's we always started off with line input.
With the gain pot and output pot at center, 12 o'clock position, and with nothing inserted, the test sine wave at fixed level should be unity. so for example if I send a 1K sine wave at +4dBu into the unit, I should have +4 on the output give or take 1/10 of a dB

 

[Jdm5149]

Yup. It’s the only one I have. Got it for 200$. Not working. I have an oscilloscope and way of sending tone. Gonna brush up on the oscilloscope workings on Sunday. Be back at it Monday. Thanks again. Enjoy the weekend

 

[TheseGoToEleven]

Got it for 200$.

Well you might have a bit of a Frankenstein to deal with, but for $200 I would've probably bit too. Fun to fix up yourself, and cheap enough that you can send it in for official repair if you don't have any more time to spend on it, or there's a replacement part you can't get.

 

[Jdm5149]

Yeah. Im kinda addicted to Facebook marketplace. I’ve gotten plenty of things cheap non working and fixed quickly. All keepers. This one is really a learning experience and I kinda like it. I want to be able to fix things in the future to flip. But for now I’ve been adding to my studio. In process of fixing house to sell and moving out of New York. Any good cheap places to move to with a music community? lol. Seriously though this is the hardest thing so far to fix. But like I said it’s great learning and getting everyone’s advice. I have a few more things need fixing and I want to keep learning. I recently got a rocktron Bradshaw switching system for 300$. It wasn’t used in awhile and I blew a cap when I plugged it in. Should have used a variac. It was ofc on the last board in the unit but I did it. A .1 ceramic. But I got it going.

 

[Jdm5149]

Yeah Greg from Avalon repair helped in the beginning but finally said I should send it in. But I like getting deals. Didn’t really want to spend 1200 for it. But in this process I’ve bought plenty of parts and test equipment. Esr meters. Transistor testers. Etc. took my oscilloscope out and gonna relearn it tomorrow.

 

[pucho812]

Yeah Greg from Avalon repair helped in the beginning but finally said I should send it in. But I like getting deals. Didn’t really want to spend 1200 for it. But in this process I’ve bought plenty of parts and test equipment. Esr meters. Transistor testers. Etc. took my oscilloscope out and gonna relearn it tomorrow.

1200? You got to be shitting me. Is that what he charges these days for Avalon repair? I am in the wrong business or need to up my rates

 

[Jdm5149]

No. I think he stated 800$ to get up to spec. Plus the 200 I paid for it. Plus I could tell it was in bad shape. I know it needs a few pots replaced. Etc…. I could tell it was gonna be in that ballpark.

 

[pucho812]

No. I think he stated 800$ to get up to spec. Plus the 200 I paid for it. Plus I could tell it was in bad shape. I know it needs a few pots replaced. Etc…. I could tell it was gonna be in that ballpark.

That’s still a ton more then we would charge when I ran their service department

 

[kags]

I’ve noticed pro audio repair shops have increased their prices (starting during COVID). I’ve had clients mention paying nearly $800 for a recapping and calibration for an 1176 and similar for 1073 recap/ cleaning. I’m all for a living wage, but those seem like $200+ / hour kind of prices.

Avalon has only one authorized repair shop and the repair prices for 737s seems to be extemely high. With such little tech documentation avail, it is a captive market.

I predict more and more older and vintage gear will go unrepaired.

 

[Jdm5149]

Well. Greg was real helpful and answered every email I sent. I have a akg 414 that needs repair and one tech quoted 90$/hr with probable 3hr need to repair. I have a Studer A820 1/4 inch which I got 10 years ago for basically free. Tachno sensor error. Tech came to my house at 150$ per hour. I guess these older units require techs that have worked on them and maybe sadly we are all getting Alittle older and sparse

 

[kags]

Well. Greg was real helpful and answered every email I sent. I have a akg 414 that needs repair and one tech quoted 90$/hr with probable 3hr need to repair. I have a Studer A820 1/4 inch which I got 10 years ago for basically free. Tachno sensor error. Tech came to my house at 150$ per hour. I guess these older units require techs that have worked on them and maybe sadly we are all getting Alittle older and sparse

Those are fair prices for expert work and Greg is a generous and knowledgeable soul.

 

[Jdm5149]

As is everyone I encountered so far

 

[Jdm5149]

So this morning I replaced r11 on the power supply board. Now I have a steady reading of 6.36 volts. Too high ? I can’t find my leads for my oscilloscope so I took reading with my meter reading AC feeding it with my digital generator 4dbu at 1k. Pad 13 : 1.030v. Pad14 : 5.28v. T9 : 1.030v T10 : .003v. Also T8 : 8.44v. T11 : 1.512v. T12 : 8.56v. Any ideas. Working on house today but I can retest later. Thanks

 

[TheseGoToEleven]

I believe Greg / Audio Rehab is $135/hr and $3-5 per part so maybe $300ish for a full recap which is 25+ caps. For an $800 estimate there would have been more work included for sure.