Com Ser Laboratories tear down possible repair - Page 1
Forum section: electronics / repair

author: Radio Tech
author_rank: Frequent Contributor
timestamp: February 22, 2014, 07:17:06 pm
content: When I quit the commercial 2 way radio business (EF Johnson) I started doing more radio repair at home in the early 90’s. I was in need of a service monitor to generate and receive signals from and to the radio under test. I found this service monitor local and purchased it. The range is 0 to 999 MHz. Just what I needed. And with the scope and trouble tracer add on I was able to check CTCSS by watching the Lissajous patterns on the scope.After a couple of years the magic smoke rolled out of the scope unit. A quick tear down revealed one of the PIO caps had exploded. 0.1uf @ 2kv. Being so busy at the time I simply unplugged the unit and continued to work. I think it was 7 years later the unit started showing its age. The signal out became distorted and had low output. This was time to start trying to obtain info on this unit. So off on the internet I went only to find nothing. Google search would not return anything on this unit. The only name branded part in the machine was the RF attenuator made by WaveTek. So I looked them up and ordered the precision resistors that were in the unit. The guy I talked to said that Com Ser Laboratories was sort of a fly by Night Company and was bought out by another company. Never did find out who that was.Later in December of 2007 a friend of mine that travels found a guy out west that had the same unit less the scope attachment. He was able to scan the schematics to Adobe and emailed them to me. These looked like they had already been scanned many times and really did not have much info on them. No part numbers or part locations. So if anyone has any other info on this please let me know.I have placed the files on my website back then for download:http://gokarters.com/smf/index.php?topic=1736.new#newThe monitor as it looks:Cover removed showing the rear of the unit. Here we can see the card tray that holds the boards. These use old style card edge connectorsThis is a view from the top showing card tray and between the tray and front panel is the mother board.The first card is the 10 MHz crystal oscillator board.Here we have the card tray lifted up. It is hinged along with the mother board also.On the bottom of the chassis you can see the power supply. This supplies:5VDC-5VDC10 VDC15VDC-28VDCHere is a closer look at the power supply boardThis image shows how the card tray pivots to allow service to the bottom of the chassis.Also in the bottom lef you can see the bras cylinder. this is the WaveTek RF attenuator.I am afraid this may be a problem. The display shows the digits, although it has no power applied. If I can fix the unit I will have to come up with a new display.This is the scope unit. It mounts on top of the generator. I am guessing the engineering department knew nothing of heat transfer back then. The main scope board mounts component side down. So a lot of heat has been transferred to the circuit board and has chard the board.Just a closer image of the scope board.This will most likely be a tough repair, so will be working on it in spare time. First thing I want to do is check out the power supply and make sure everything there is up to spec.Thought I share a bit here.

author: Radio Tech
author_rank: Frequent Contributor
timestamp: February 24, 2014, 01:03:52 am
content: What schematics I have on this old beast is located herehttp://gokarters.com/smf/index.php?topic=1736.0

author: Radio Tech
author_rank: Frequent Contributor
timestamp: February 24, 2014, 10:34:57 pm
content: I decided to work on the scope unit first over the week end. Then I noticed that none of the schematics covered the scope. So that gave me another set back. To day after looking the CRT over I notice that the model number looked close to another piece of equipment I just finished up.And that was a Kenwood SM-220 station monitor.The CRT is Hitachi 75AVB31The Kemwood is a 75ARB31So maybe I can reverse this by using the Kenwood manual and get the scope back up and running.

author: Radio Tech
author_rank: Frequent Contributor
timestamp: September 12, 2015, 01:45:00 pm
content: I know this is an older post but wanted to post new information in here for those that are in need of it.So if you have the scope trouble tracer unit on your Com Ser generator you will find there is no material as in schematics or whatever on this unit. After many months of cross reference to the tube "Hitachi 75AVB31" you will find that the "Beckman BK 1405" scope is the same scope used in this unit.Here is the link to my site with the schematic attached in the post;http://gokarters.com/smf/index.php?topic=2402.msg18083#msg18083I had 2 burnt resistors R162 and R163 in mine. Could not read them even with a meter. This helped me to determine what they were.

author: Fraser
author_rank: Super Contributor
timestamp: September 12, 2015, 02:48:16 pm
content: Thanks for posting this thread. Though I know nothing about your unit I appreciate seeing inside it.From the top deck of the main unit it looks logically laid out and pretty well designed. The below deck pears somewhat less organised. The CRT unit was likely robbed from another manufacturer as you have discovered. Far easier to use someone else's design than to build your own. It is, after all, a simple CRO assembly. Very well done for identifying the OEM. That must have been quite a challenge.With regard to documentation, I have often found that equipment that is pre-Internet and PC era does not have documentation available. It needs someone with the paper manual to scan and upload it. For rare and unusual equipment that sadly does not happen often.I see that no one else commented in this thread. I am interested though, so please continue to update this thread. Others can learn from it. Working with little or no documentation forces us techs to revert to basic principles and our knowledge of how a circuit or component should work. With your background you are obviously well qualified for the task. Others may learn from your experience on this equipment.I will continue to keep an eye out for the LCD that you require.All the best with the repairFraser(Aurora)

author: Radio Tech
author_rank: Frequent Contributor
timestamp: September 12, 2015, 04:11:22 pm
content: Quote from: Aurora on September 12, 2015, 02:48:16 pmAnd thank you for taking the time to read it. I am the same way, I love looking inside electronic stuff I never seen before and appreciate folks sharingQuoteIt reminds me of several engineering departments built each section separately and then brought it to the table to assemble lol. Like they never communicated with each other, and this was the outcome.I cannot even remember how long I had this unit. But I know I have searched from day one only to find very little about it. As in my previous post there is schematics for the generator but were very poor.Before the paper ID tag on the back fell off my serial number was in the high 10 thousands. So thinking there were quite a few of these built in the early 80's. I see a lot of 1981 to 1982 date codes on IC's and stuff. I did find a amateur radio operator (W9GB) that knows a lot about different things told me that the company has been long gone. So they were a fly by night company that produced these and disappeared.So we now know that the scope unit is base off the BK 1405 5MHz scope. And yes this did take a long time to figure out. Surprised at how many scopes and equipment used this tube. When I ran into the BK1405 the circuit designed grabbed my attention. After looking it over I compared the unit and schematic and found I had a match. Even the silk screen on the board is the same as the schematicAs far as the RF generator section It was probably designed off one of the Wavetek units. The RF attenuator is also Wavetek branded and is still available for several hundred dollars.QuoteAgreed!And is another reason I like doing this. Get out as much information as possible through my research and repair of this unit. And if I can ever get it back to working condition then I can re-draw schematics with voltage reference and documentation. Sort of reverse engineer the thing so one day it may help others.QuoteI have found that no one replies to a lot of my post. But that is ok. I see hundreds of views on my own website but it is pretty much dead in activity. All that matters to me is folks finding something of use and that is helpful to them. The schematics I posted on my site have been downloaded many times. So I know folks are looking.And again thank you for your interest in this. Just reading your reply helps fuel the fire with in to continue on this adventure. I can say if has been a tough one. I agree about working with no documentation. But it helps us to learn more in the long run AS soon as I am finished with the scope unit I will pull the LCD and see what the back side shows up. Maybe a id number if luckySo as far as the scope unit since I have some documentation on it. Unidentified resistors have been replaced. The 4 oil filled caps that I removed some time ago have been replaced with ceramic style caps for the time being. I do not have any direct replacements in stock.Just to get the circuit under test:C123 and 126 were .1 @2KV and were replaced with .1 @2KV ceramicsC124 and 125 were .1 @1KV and replaced with .1 @1kv ceramicsInstalled a new .5 amp fuse and powered the scope on. Nothing, no power LED, no bang, no smoke.Starting with the mains connection to the transformer I found I had primary and secondary voltages. Checking DC power at the LED found it was blown. Replaced with a green LED.No trace on CRT but I do have filament voltage on the board. Cannot see it in the tube but I know some are hard to see.PS:I also wanted to add. Since there is little information on equipment like this, take lots of pictures.Of wiring connections, part placement, control wiring ect. Some wiring becomes brittle and will break loose. Leaving you with "where the heck did this go". This has already happened to me several times in the scope unit. There was a small red wire dangling from the power LED indicator. No where on the board could I find where it broke loose from. After reviewing some pics I took earlier I found the wire was attached to a resistor that has it's body raised off the board. So looks like this was an after thought for a connection point when the unit was built.I feel I made some good progress today

author: Radio Tech
author_rank: Frequent Contributor
timestamp: September 12, 2015, 06:25:44 pm
content: After finding yet another missing resistor(R167 not sure how I missed it) I powered the scope on.After a few seconds I saw a green tint on the CRT. I started to adjust controls and what do you know, there was a trace on the tube. The intensity and focus controls had no affect but the trace was about 4 mm thick, not too bright but not too dim. 2 minutes into the test it began to fade away. No smoke or bang but for 2 minutes I was very happy and now can start more troubleshooting.At least this test shows me that most of the circuitry is working. Now to start back verifying power supply rails specially in the HV circuit and focus control stuff.

author: Radio Tech
author_rank: Frequent Contributor
timestamp: September 13, 2015, 12:11:02 pm
content: Just a bit of information.There was a company in Florida called Lampkin Laboratories. Made certain FM test gear.I hear that Com-Ser Labs was previously Lampkin and the BR1000a was their last model.

author: Radio Tech
author_rank: Frequent Contributor
timestamp: September 14, 2015, 12:44:09 am
content: The scope unit looks promising now. Going to order a few high pressure diodes and some new caps for it.Possibly this week I am going to do a video on this generator.

author: Radio Tech
author_rank: Frequent Contributor
timestamp: September 21, 2015, 12:03:41 am
content: I have uploaded a overview of this unit on YouTube.

author: Radio Tech
author_rank: Frequent Contributor
timestamp: September 22, 2015, 12:07:05 pm
content: Just another update.Spent last evening checking voltages on the power supply board. All voltages were spot on. No problems there. I did notice 2 diodes in a bridge rectifier circuit runs a little warm. But voltage was fine. May dig into that more later. Next I need to check power rails on the different boards to make sure all are correct.Then I will move onto signals and verify those are correct.

author: Radio Tech
author_rank: Frequent Contributor
timestamp: September 24, 2015, 11:45:46 pm
content: I have verified a lot of the signals are present in the unit, however we do know what is not working.When the unit quit working it would not receive on air signals nor would it generate a signal. First though would be PLL issue.But a few years down the road while testing the display goes out. Possible that the two issues are related? not sure. Will try and get more testing done this week end.