Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Parts Where to get, and how to make the best bits. PCB's, caps, transformers, etc.

ALPS Motorized Volume Pot- Repair (VTL 5.5 Preamp)
ALPS Motorized Volume Pot- Repair (VTL 5.5 Preamp)
Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 4th April 2018, 01:40 PM   #1
Arniespin is offline Arniespin
diyAudio Member
 
Join Date: Aug 2017
Default ALPS Motorized Volume Pot- Repair (VTL 5.5 Preamp)

Hi folks,
Need some help diagnosing a strange problem with my VTL Preampís Volume pot. It uses an Alps motorized pot, that is controlled via the remote. When I turn on the VTL, the remote controls the volume normally for the first couple of minutes and then stops working.

Manually the the volume pot works perfectly, smooth, precise and with no crackling. Iím guessing that there is something happening when the preamp warms up that cuts off the remote control of the pot.. any theories?

im pretty handy and would feel comfortable trying to perform a repair myself, but could use some experienced advice.

Thanks!!
  Reply With Quote
Old 4th April 2018, 01:54 PM   #2
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
ALPS Motorized Volume Pot- Repair (VTL 5.5 Preamp)
Nope, no theories

Have you a scope ? You need to look at the output of the remote receiver and make sure it is OK when the fault occurs.

No scope. You could look at the DC voltage on the output pin and see if it fluctuates in the same way when faulty as when working.

There will only be 3 pins on a typical receiver, a 5 volt supply, ground and the output pin. The output pin may be normally also at 5 volts until it becomes active.

Don't discount remote control issues. Point it at a digital camera and confirm you can see it transmitting OK. You will see the LED light as cameras are sensitive to infra red.
  Reply With Quote
Old 4th April 2018, 05:29 PM   #3
Arniespin is offline Arniespin
diyAudio Member
 
Join Date: Aug 2017
Hi Mooly! Thanks for your help!

I forgot to mention that all the other buttons on the remote (Mute & phase-shift) work fine, it’s only the Volume that stops working.

I’ll get inside and do some testing. Will the 3 pins be directly on the back of the infrared reciever?
  Reply With Quote
Old 4th April 2018, 07:02 PM   #4
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
ALPS Motorized Volume Pot- Repair (VTL 5.5 Preamp)
If other remote functions continue to work then its not going to be the receiver. I suppose you still have to confirm its transmitting though (camera).

Its difficult to describe what to check without having a unit in front of me.

The motor will be driven from something called an 'H Bridge' (look it up and do an image search for that). You would need to check the supply to the bridge is present and also to identify the logic inputs to bridge and confirm that they change state as they should.

The bridge could well (quite likely) be a chip and not discrete components.
  Reply With Quote
Old 4th April 2018, 08:57 PM   #5
Arniespin is offline Arniespin
diyAudio Member
 
Join Date: Aug 2017
Okay, I seem to have found the h-bridge section. I'm linking a photo of it. I see a chip on there so that might be the culprit.
Attached Images
File Type: jpg IMG_0248.jpg (660.8 KB, 93 views)
  Reply With Quote
Old 5th April 2018, 07:33 AM   #6
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
ALPS Motorized Volume Pot- Repair (VTL 5.5 Preamp)
That looks promising.

First step would be to try and figure out the configuration of the bridge. I would guess that there is a positive supply voltage on the emitter of one pair of those transistors and that the emitters of the other pair go to ground.

If so, is the supply present when the fault occurs ?

Can you identify the feeds that control the bridge ? That could possibly be R1 and R3. Try and see what happens to the voltage on those resistors at the ends that are near the chip.

Measure the voltage on each when static and when pressing up and then down. I would expect something like 0 and 0 when static and 0 and 1 for 'up' and 1 and 0 for 'down'.

That kind of thing. It is possible the logic could be reversed with 5 and 5 volts static.

What you are looking for is something that is different between faulty and non faulty states.

Freezer spray might help if the fault occurs when warm. You would just drip some on the transistors in turn and then the chip. Don't blast the parts as that chills far to wide an area. Single drip at a time.

Air duster cans with a straw (the cheapo butane filled ones) will work as freezer if you invert the can.

Is the chip a PIC ? What are the numbers on it. Tbh the chip is always the last suspect though.
  Reply With Quote
Old 5th April 2018, 07:37 AM   #7
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
ALPS Motorized Volume Pot- Repair (VTL 5.5 Preamp)
Jut thinking about the remote again... the volume button requires constant transmission from the remote and it could be failing under those conditions.

You have to at least do a basic check that it is transmitting constantly when you press the button. That is the camera method and measuring the voltage on the receiver output pin to make sure nothing changes when the fault appears.
  Reply With Quote
Old 5th April 2018, 03:31 PM   #8
Arniespin is offline Arniespin
diyAudio Member
 
Join Date: Aug 2017
Very encouraging! Thank You Mooly!
Now I have a plan of action. I’ll pick up some freezer spray and begin testing this weekend. Will report back soon.
  Reply With Quote
Old 5th April 2018, 05:16 PM   #9
rsavas is offline rsavas  Canada
diyAudio Member
 
Join Date: Aug 2012
Location: Ontario
The motorized pot is controlled using a mcu usually. I have seen the control done with "H" bridges and also in one elektor design, the pot was driven directly by the mcu pins that were wired up in parallel in order to provide the current necessary to drive the pot motor.
Debug the remote as Mooly suggests, the pre-amp will have a IR receiver chip that will translate the IR light into electrical signals for the mcu to decode. Look at the IR Rx o/p (3 legged part on the front panel) to determine if is receiving the codes from the IR Tx(remote).

I have also tore some intermittent remotes apart and cleaned the contacts on the pcb and the black carbon on the rubber portion with a qtip & alcohol. Mom split tea into hers :-)
They are a PITA to pull apart.

Last edited by rsavas; 5th April 2018 at 05:19 PM.
  Reply With Quote
Old 5th April 2018, 06:56 PM   #10
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
ALPS Motorized Volume Pot- Repair (VTL 5.5 Preamp)
An interesting tale of remotes (I used to work in a busy service dept) were the ones that appeared to have had coffee or coke spilled onto them. You pulled them apart and the rubber keypad was all gooey and sticky... and the customer flatly denied it.

Now while its true that spillage was a big big issue, I found out years after rubber keypads became the norm that the actual material used could leach the plasticizer used to keep them supple and that this was in fact the cause of the goo in some remotes.

I feel a bit guilty now thinking of the customers wrongly accused.

There is a knack to opening remotes without damaging or marking them. An old credit card works wonders for sliding down the join and snapping them open.
  Reply With Quote

Reply


ALPS Motorized Volume Pot- Repair (VTL 5.5 Preamp)Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
SIMPLE remote volume control with alps motorized pot ChopperCharles Tubes / Valves 23 3rd June 2016 03:13 PM
Retrofitting Old Preamp with Motorized Volume Control Jmo Analog Line Level 11 9th April 2016 12:22 PM
Adcom GTP 500 Preamp Motorized Volume Controll saralieberum Solid State 0 22nd December 2010 11:39 PM
Alps RK27112 10K Motorized Blue Velvet Volume Pot raghoser Parts 4 28th January 2008 02:24 PM
Remote Volume Control + Extra board + Alps Motorized Pots jamesjung21 Swap Meet 12 23rd November 2006 09:03 PM


New To Site? Need Help?

All times are GMT. The time now is 04:25 AM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 14.29%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Copyright ©1999-2018 diyAudio
Wiki