Re: Revox A77 MKIV, No play speeds
On this model capstan is always on regardless of function.
On this model capstan is always on regardless of function.
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Re: Revox A77 MKIV, No play speeds
thanks... I couldn't find anywhere in the manuals (user or service) that indicated that but seem to recall from a long time ago the suggestion to not leave unit powered on if it wasn't playing / recording anytime thereafter.
I have started some re-assembly and hoping it goes back together. Trying to figure out if / how the brakes get adjusted. I had to take the plate off to get at the screws for the power board. It seems the "brake band" has some slight "drag" on the hubs as they are turned by hand... I haven't powered up and pressed any functions yet.
edit: put back enough stuff to watch the hub spin, test the brakes and such. With the EOT (end of tape) sensor blocked, brakes and hubs seem to function. In play, all motors are running... although I haven't figured out if they are correct. My head spins watching the things all turning at once. I assume that take up and feed reels turn as some speed corresponding "closely" to the selected tape speed with adjustments to the tape wind levels on each spool. Won't get tape mounting for a bit as the next tests seem to fail. These are dealing with input and meters. I can only get the ch1 level meter to register some activity and that's only when selecting "MIC" at the meters. ChII shows nothing at all positions. Further, I am using AUX input from the back so I am not sure why the system detects it on "MIC" as opposed to AUX. Potentially, a switch board issue maybe. I can hear the input thru the headphone jack. I don't think it is showing up on both ears but I need to recheck that. Baby steps continue.Last edited by budwich; 06-29-2021, 07:26 AM.Comment
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Re: Revox A77 MKIV, No play speeds
solved one "mystery" about the inputs... "finger problem" when I was looking at the case labelling, it was upside down and I didn't take that into account when plugging into the back of the body of the machine and I had plugged into the rear mic input as opposed to the aux input. So that solves the "wrong input" but the problem of no chII VU output showing on either position appears to indicate a problem on that input amp or selector... probably the amp. I have to do some signal tracing to see where things are going "flat".Comment
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Re: Revox A77 MKIV, No play speeds
I can hear some sound coming to the headphones on chII with the rec VOL cranked full but the VU shows on a slight "voltage". There is continuity from the input RCA plug to the input amp board pins for chI/chII so the signal is likely getting into the board. I have to find accessible areas on the board to check for live signal while powered, the card connector is too far in to easily probe.Comment
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Re: Revox A77 MKIV, No play speeds
on page 55 of the pdf (for the input amplifier) that was attached to this post (earlier in the thread), the 10v "test point" (in between the output transistor "pair") is 19v volts on chII while it is 10.4v on the working chI. Possibly a shorted or non-operational transistor???Comment
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Re: Revox A77 MKIV, No play speeds
Found a faulty transistor in chII, q401 (bc179) at the front stage of the input amp. Hopefully, that's the one problem at this signal point.Comment
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Re: Revox A77 MKIV, No play speeds
Got a replacement transistor (nte234 as an equivalent). Now have VU meters working for both sides following the input signal levels. Moving towards checking outputs with a tape, hopefully everything will be fine including speeds and signal characteristics.Comment
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Re: Revox A77 MKIV, No play speeds
good progress on this. Put on an old tape with a recording from a long while back. It plays and sounds fine. Of course, the tape and my ears have aged so it might be relative. I have to find some unused tapes or portions there off to check the recording results but it appears that the unit is fully functional / operational. Thanks again for the pointers and hints along the way which helped me get to this end point. Its very "nostalgic" watching the big tapes roll and play my "defined playlist".Comment
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I have a Quantum SuperLoader robotic tape library that uses an IBM LTO 7 tape drive which is constantly complaining that it needs cleaning. If you insert a cleaning tape, it performs the clean and resets the cleaning counter to 0 hours. It should only require cleaning every 50 or so working hours but after as little as just 1 hours use it requests cleaning. We've purchased a new cleaning tape along with new LTO backup tapes but that has not resolved the problem.
I have taken the library apart and can see no noticeable signs of dust inside. I have removed the tape drive from the... -
Problem
This is an LG edge LED lit LCD Display. The LEDs are on the bottom edge of the display. There are 2 bars (left and right) Each bar has many LEDs and a 6 pin connector. Each pin drive several LEDs thus is the highest current flow / heat junction. The weak lead free solder gradually fails with thermal expansion/contraction cycling and increases resistance. PSU will compensate up to a point, then when the current is too high, PSU just shut down the backlight causing a dark display. I have even seen one which the connector just fell off as solder points became completely detached.... -
I've been seeing a lot of the new TVs (samsung and LG only i think) maybe 1-2 years old suffering from sudden panel death and have been over 50% successful bringing them at least most of the way back to functionality if not all the way, with the tape masking of the LVDS pins method.
add this one to the list. the issue was on the left side of the panel and i ended up blocking just 3 pins on the connector that joins the two panel boards that make up the left side of the panel (it has 4 boards total) i didnt get the picture back to 100% perfect. i spent hours fiddling with which pins to block...07-17-2023, 10:22 PM -
Hi,
I got this VCR in compensation and well, It wouldn't be fun If I didn't f*** something up doors that won't close completely was easy fix.
I was thinking that someone who messed with VCR before me didn't screw all the way this screw(see picture), but later I found out that this screw is suppost to be like that smh... and now after I clean head and everything I got this kind of situation on video (see videos)
- on first play I got black and white/color exchange white some noise and picture is flickering
https://imgur.com/ygMXcWI
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Hi everybody.
i'm looking for the black tape inside apple's devices.
Is the tape tha covers the shield on the mainboard. when you take it out, loses the adhesive.
It is very thin.
can somenone help me to find it for a better repair?
Thanks, God bless you.
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