Heathkit GR-900 Build Thread!
 

I just scored an UNBUILT Heathkit GR-900 25" color TV kit at the NJARC auction yesterday, and I am going to document the build process here on VK. I have always wanted to assemble a "real" Heathkit TV, after building countless smaller heathkits over the years. I did build one of the mid 80s TV kits for a family friend while I was in high school, but those were simply unassembled Zenith System 3 sets, with all the modules prebuilt, taking away most of the fun.

Anyway, this set was part of a Bell and Howell/DeVry TV Repair training course, and in addition to the 7 (!) standard Heath assembly manuals, there are 5 manuals of "Color TV Experiments" to be performed on various modules and subassemblies during the build, but they require additional parts and an experiment console which didn't come with the set. So I will be building the set in the straightforward manner as the normal Heathkit customer would. This is an early 70s vintage set, which is 100% solid state with the exception of the HV rectifier and CRT. It is built on multiple plug-in PCB modules, which are then plugged into a vertical metal chassis. It was apparently bleeding edge stuff in the day, with a varactor UHF tuner and automatic fine tuning. There are several integrated circuits used, in addition to the dozens of transistors. The tuners, IF, AFT and HV section come preassembled and aligned at the factory, but there is a LOT for the builder to do, unlike their later sets.

Several boxes of this kit had already been opened and dug through, so I started with a COMPLETE inventory to see if everything was still here. On the plus side, the original purchaser apparently received a double shipment on one package, so I have a spare VHF tuner, as well as spares for the IF module and all the parts to build up additional Chroma, 3.58 oscillator, and AGC/Sync modules. Also found was the optional GRA-900-6 ultrasonic remote control kit! :banana:

On the downside, I am MISSING the audio and vertical output transformers!:cry: I have posted a want ad here on VK, as well as the Yahoo Heathkit list looking for these, and if anyone can help here, PLEASE let me know. It would be a shame for this set to never run because of 2 missing parts. Hopefully, replacements can be located for these, or I am going to end up with a handbuilt electronic doorstop. Another issue is that the NOS RCA 25VABP22 was apparently stored in a damp location that rotted the box away and may have caused a cataract around the edges of an otherwise virgin CRT. Hopefully, it will not be too visible once the CRT gets installed into the mask. A cataract removal or CRT replacement could always be done if the results warrant it.

Anyway I will be getting underway with the build tonight. Because Heath intended even their most complex kits to be buildable without anything more than hand tools and a soldering iron, the first thing that the TV builder needs to assemble is the "Troubleshooter", which is a simple 5 range VOM used for testing the rest of the set as the build progresses. It is then installed inside the set (along with a built-in Bar/Dot generator) to be used for future troubleshooting/adjustments as needed.

Next up--Building the "Troubleshooter"! :D

I had to scrap a 20" heathkit tv a few years back...because the cabinet had gotten RUINED In my old garage. it was SS, with SCR deflection--maybe a HV rect tube--all else modular SS. I kept the tube and chassis, MAYBE the tuner. Know where the chassis is right now. it DID use a large TO-66 audio amp, IIRC. SO--it must have an output transformer. Pretty sure it also had one large vert transistor for the V-out..but will have to look again...

I just KNEW...there would come a time...someone would be needing some part from it...

I just looked at an RE magazine from late 1970--my set is there. Looks like a GR_270, 20 inch version. it DOES use a v-out transformer, and a TO-3 transistor mounts on the chassis right above it. is your chassis like this.

Also--the A-out transistor is on the left, above the power tranny, there are a pair of transsitors, but I do NOT think both of them are for audio.

Definitely sounds similar to my set. I have a lead on a junker chassis from a local VK member, which I am going to look at in a couple days. If that doesn't work out, I will let you know. Thanks!

I am amazed that within a couple hours of posting, I now have THREE potential sources for these 2 obscure 40+ year old parts lined up! Thought I would be looking for months. The power of the internet....:thmbsp:

After about 15 years on the net...I wonder....just HOW we did it before then. Me, mainly the old "tradin' post" paper--I found a lot of things through that...and of course, word of mouth and the curb...from the beginning.

This tv came from an auction--in about '93, that I did NOT attend...but I ended up with this set form the guy who DID attend. IIRC...it DID work...and had the cabinet not been hopeless...i would still have the complete set. Buty..water and rats do take their toll...

Since Heathkit used RCA's SCR sweep I wonder if they also copied the
vert out from one of the early XL's ?? A lot of RCA in them.

The audio should be easy, if they used the high collector voltage
transistor one from a Zenith hybrid should work fine.

73 Zeno:smoke:

Got started on the build by putting together the "Troubleshooter", a simple VOM that Heath included in the kit to aid in testing and repairing the set as needed. Heathkit really went out of their way to make sure that just about anyone could successfully build one of their kits, without any need for specialized tools or test gear. They didn't assume that anyone building a TV kit actually knew anything about electronics, or already owned a multimeter. They didn't even assume you would have access to "exotic" tools like a 1/4" nutdriver, so one was included with the kit, as well as a small open end wrench and the famous red plastic nut starter. As you can see, they even included an Eveready zinc-carbon AA cell, which I was AMAZED to find not only hadn't leaked over the last 40 years, but still read 1.5 volts on my DMM! I didn't install it, though, opting for a modern alkaline AA cell instead. Will keep the included one around for laughs. Haven't seen one of those since I was a kid.

This is a 5 range DC voltmeter and ohmmeter, which also includes a special A-B-C-D-E scale to be used by non technical types to verify that a certain reading is within an acceptable range, such as resistance checks of power supply rails prior to applying power, etc. Function and range selection via a pair of 3 position slide switches. Ranges are 5, 50, or 500 VDC, and R x 1k or R x 10k for the resistance ranges. This meter was only sold as part of their TV kits, not available as a stand-alone kit.

The build itself was obviously pretty simple. The meter, switches, pot, and battery holder get mounted into the case, then the components are wired together point-to point. There are 3 precision resistors for the voltmeter ranges, and a few other resistors and diodes for the ohmmeter and meter overload protection. Construction took a leisurely hour or so, thoroughly enjoying the Heathkit experience again after many years. The meter tests out fine, and was set aside to await installation into the rest of the set.

Next up: The TV build itself gets underway with the Audio module...

Are you replacing the electrolytics that came with the kit with new ones?

I'd be a bit wary building such a rare treasure with 40-year old caps.....


Cheers,

I am going to carefully reform the 2 multisection cans on a power supply, and see if they drop down to acceptable leakage current values.

The smaller low voltage ones will be tested for capacitance and ESR, and replaced if warranted.

About 5 years ago, I replaced the original carbon zinc Ray-O-Vac battery that had been in my V-7a VTVM for over 50 years with a new Duracell. Recently the meter was observed to be somewhat erratic... turns out, the Duracell had leaked extensively, causing some damage to the circuit board. The old Ray-O-Vac is *still* leak free, but is down to 1.43 Volts.

jr

Back to the build! First off, a big thanks to Tim for supplying replacement audio and vertical output transformers for this set! :thmbsp:

Got started on the first PCB assembly, the Sound module. This module implements essentially the entire audio section, with the exception of the chassis mounted power output stage. It contains 2 transistors, one IC, and a ceramic 4.5 MHz IF filter.

Most of the modules in this set use tubular contacts on the PC boards, which mate with pins mounted on the chassis. Construction begins with the installation of these contacts, which insert into 2 rows of square holes along the top and bottom edges of the board. A plastic alignment jig that resembles a lego block is placed over each row of contacts, the contact tabs are bent over to contact the foil pads on the board, and the tabs are soldered down to the board. Once the soldering is complete, the alignment jig is removed, leaving a properly spaced, straight row of contacts. The kit provided a long length of 3/16" diameter black PVC tubing, which is cut into short lengths and slipped over the contacts to provide protection against shorting adjacent pins. The provided tubing was pretty sticky and in poor condition from plasticizer breakdown, so I substituted some red heatshrink.

The board is then stuffed in stages, starting with a jumper wire, followed by the resistors, IC and transistor sockets, capacitors, inductors, and the IF filter and coil. Finally a short 2 -pin cable is attached, and the semiconductors are installed in their sockets, completing the module.

Next up: The Luminance module.

More pics:

Never having built a kit myself, just luuuv seeing this one go together.:yes: Built a few projects from the schematics Heath used to put in their catalogs, though. They all worked, too.

I still think there's a bunch of miswired freaks out there wishing death upon you because god forbid you assembled a heathkit set.
What's the point of owning the kit if you don't want to assemble it? :thumbsdn:

There was at least one person on the Heathkit list who couldn't understand how building the set was more rewarding than flipping it for $ on eBay.

Back in the mid-'70s a friend (and still good friends today) built one of these. Never could get it aligned quite right. At the time we had a Heathkit store down on Ross Ave. in downtown Dallas. He hauled it there and they aligned it. Knockout excellent picture!

I got a lot of my initial experience building Heathkits and Knight kits for myself and friends. One of my first, a Heathkit tube clock radio from about 1963, I still have.

What Heathkit list? I'd love to go there.

WANTED: unbuilt or built, alive or dead, Heathkit GR-180 TV

WANTED: Alive, very alive only, correct picture tube for above.

The GR-900 build continues..

Next up, the luminance module. This module incorporates the standard luminance circuitry found in any color set, in addition to the dot generator circuitry used for the convergence setup. The dot pulse generator circuitry incorporates a relaxation oscillator based on an NE-2 neon lamp, followed by some wave shaping circuitry.

Testing a sample of the original electrolytics showed that most of them were acceptable, but a few showed borderline high ESR, even after reforming for a few hours at or near rated voltage. I decided to replace all the small electrolytics as cheap insurance against problems. The 2 large twistlocks for the main chassis seemed to reform perfectly well, and will be used. Replacing the electrolytics on the smaller modules allowed me to get radial lead types where needed, rather than the rather ugly vertical mounting of axial caps that the board layout originally called for.

Next up--the Video Output board.

I have the same TV. Is this the cabinet you have? I got mine from a guy at work who built it as part of a correspondence course. It had sat not working for many years. I fixed it (blown rectifier diode) and it is my daily driver. It has the original electrolytics. Its had other problems - it would not color sync and also there was a problem with dirty pots, but it's been working pretty good lately. Also I had to replace that main circuit breaker with a fuse as that was shot.

There is a yahoo group on Heathkit TVs but they don't seem to be active lately.

https://groups.yahoo.com/neo/groups/...tions/messages

My kit came with no cabinet, which I understand was somewhat common with the home training courses. Apparently, many veterans enrolled in these courses, which were paid for by the GI Bill. The government would pay for the training course, the test gear, and the TV kit, but not a piece of furniture with no educational value. Lots of these sets ended up in built-in installations. Not sure exactly what I will end up doing with the set when finished with it, but I am considering a homebrew clear acrylic/polycarbonate cabinet to show off the guts.

Anyway, some progress has been made in the last week, beginning with the Video Output module. This board contains the RGB decoder IC, the 3 CRT cathode driver stages, and the 3 drive controls.

So far with this build, there have been very few issues with solderability of components. One of the exceptions was the 3 section drive potentiometer on this board. The wiper terminal of each section had acquired a thin layer of a dark tarnish that thoroughly resisted the action of soldering flux. A quick cleaning with a tiny wire wheel in a Dremel tool cleaned them right up, though.

Next up, the Chroma, 3.58 Oscillator, and AGC/Sync modules, along with a guest builder who helped out last weekend. :thmbsp:

Wow! I never saw the schematics in the catalogs... I only got into Heathkit in the 1970's and '80's however. Were these schematic laced catalogs earlier than that?

Looks like a fun project. Impressive that they used G10 epoxy circuit boards.

If I ever find an un-built Heathkit TV I'd have to build it too. :thmbsp:

Wow what a thread! I would be so excited to be embarking on this project. I know where there is an unbuilt color Heathkit locally but the guy is insisting on keeping it in original box. Not sure which set it is but, he claims to have acquired it in the early eighties.
The parts stock seems to be of nice quality on yours. Probably a good move to perform a leakage test on the original capacitors.
Say, if (heaven forbid!) one of the ICs were bad, would a replacement be procurable on its own, outside of a whole kit?
Not too many people left today who could say they actually built their own TV set!

More likely "boxes".

I know where 3 unbuilt color TV kits are right now. I don't expect they're going anywhere soon.

.

Yep. I suppose I can see the desire in keeping the "boxes" sealed but I offered this fellow good money in cash and he wouldn't even hear it!
Plenty of old sets out there still...it is amazing really

This was the late '50s.

Wish I could find a unbuilt tube Heathkit TV. That would be a fun project.

They're still around, sometimes right under your nose. Got my latest one at the ETF convention this year when the rest of you guys were off to lunch! My van was packed to the roof on the return trip. This one included the multimeter and tube tester kits with it.

.

Did not see it..or perhaps I too would have bid.. But I got enough from the ETF this time... INCLUDING the BW set in my avatar...certainly NOT disappointed !!

All of the ICs in this set were (or went on to be) industry standard stuff of the day. Mostly Motorola and RCA linear ICs, most of which were second sourced by other vendors, and were available from ECG, SK, or NTE at least at one point. Same types of chips that started showing up in other manufacturer's sets of this era.

This kit had already been unpacked and partially gone through, and I received it in 2 large boxes, 4 smaller boxes (one for the remote control option), and of course the CRT carton. One of the smaller boxes was apparently a duplicate shipment. Not sure if the training classes shipped the whole kit at once, or in multiple shipments to each student.

Anyway, the build continues on board by board. My best friend and her daughter were over last weekend (Daughter needed help with replacing a fuel pump on her car that we had diagnosed as bad a few weeks earlier), and she was asking about all the boxes of parts down in my basement shop. I told her that I was putting together a DIY TV kit, and she was intrigued with the idea of building your own TV. Showed her a few of the modules I had been working on, and she was so interested in it that I gave her a few quick lessons on soldering, and turned her loose on the Chroma board (which was one of the ones I had a spare for from the duplicate shipment). She did an AMAZING job putting it together, and wants to drop by again to do some more on the set, before I finish it all. :thmbsp: By the end of putting the board together, she was already starting to learn the resistor color code, too...:)

The Chroma, 3.58 MHz oscillator, and AGC/Sync modules all went together that afternoon. Here's some pics of the finished board, plus a shot of my soldering student in action....:smoke:

Up next, Vertical Oscillator, Horizontal Oscillator, and Pincushion modules....

The last 3 of the plugin modules are completed and ready to go. Construction is much the same as the previous ones. Here we have the Vertical Oscillator, Horizontal Oscillator, and Pincushion modules. I have been replacing the electrolytics with modern equivalents as I go along.

I have tested a random sample (maybe 25-30) of the resistors during the build, and have found the values within tolerance (some just barely). Solderability of the boards remained very good through 40 years of storage, and almost all of the components have been perfectly usable right out of the box, as well. Some of the diodes which had silver plated leads had a bit of tarnish on them, but it wiped right off. The CTS brand trimpots were the only major soldering problem, with the wiper terminals refusing to take solder until I heavily wirebrushed the terminal (removing whatever the plating was and exposing the brass underneath). Not sure what the plating is, but it develops a thin brownish/purple tarnish that solder flux does nothing to. The end terminals of the pots are just fine, having what appears to be a tin/lead coating.

The final pic here are all 9 of the modules completed so far. Next up is the convergence panel....

The convergence panel is the largest PCB so far. It houses the usual array of wirewound pots and coils used for the dynamic convergence adjustments. It is mounted on a small subchassis, along with the UHF tuning presets and several secondary/service controls. It uses 6 silicon diodes rather than the traditional selenium convergence diode assembly found in most commercial sets of this era.

The UHF preset tuning assembly is similar in concept to the preset tuning panels that became common a decade later in early VCRs. It consists of a carbon film resistive divider, with 12 separate adjustable sliders to set the varactor tuning voltage for the desired UHF channels.

Most of the wiring comes in the form of prefabricated harnesses which are soldered to the various points on the subchassis. The 3 convergence magnet assemblies that go around the CRT neck are attached to one of these harnesses, and the other harnesses have connectors that will get plugged into the rest of the chassis at final assembly.

The convergence panel completes the first of the assembly manuals. Before moving on to the next manual in order, I am going to go through the assembly of the optional remote control, which has its own manual, separate from the ones for the set itself. The next post will deal with the assembly of the remote control transmitter...

Got started on the GRA-900-6 remote control, by building the handheld transmitter unit.

Unlike the Zenith type mechanical transmitter using ultrasonic chimes, the Heathkit design is electronic, consisting of a very simple 1-transistor Hartley oscillator, driving a small ultrasonic transducer. 8 separate ultrasonic frequencies can be generated by pressing each end of one of 4 rocker style buttons. Functions include on/off (which can also select one of 3 audio levels), UHF/VHF select, channel up/down, color up/down, and tint red/green. Each function button contact switches one of 8 precision (2%) silver mica caps into a single transistor oscillator circuit. The circuit is powered by a standard 9V battery.

Construction was pretty straightforward, with only 2 age-related issues. The 16 small brass rivets used for the board mounted switch contacts were pretty heavily tarnished and needed a good cleaning in order to be soldered onto the board and make reliable contact with the rocker leaf switches.

The other problem was that the provided foam tape had completely dissolved into sticky goo that was all over the bare PCB. Luckily it cleaned up well with IPA, leaving the board unharmed. The foam tape was replaced with a modern equivalent weatherstripping tape, and is used to cushion the battery and ultrasonic transducer inside the 2-part plastic housing.

For some reason, the remote transmitter and receiver PC boards are phenolic based, rather than the nicer epoxy glass ones in the rest of the set.

After finishing the remote transmitter, I installed a battery to see if it worked. I tried plugging the TV receiver microphone into a scope (it has an RCA plug cable attached) to see the signal, but saw nothing at all. A quick look at the receiver schematic shows that the microphone needs a 200V or so bias voltage which the receiver provides. I connected my scope probe right across the transmitter output leads, and got nice strong sinusoidal signals right at the transducer, with a different frequency for each button pressed, so the transmitter seems to be functional.

Up next, the remote receiver and the first hints of trouble ahead?

Next up on the bench was the remote receiver unit that goes inside the TV itself. The receiver consists of an ultrasonic microphone, a wideband preamplifier, and 8 separate LC tuned circuits driving 8 relays which then drive the control motors and other set functions. The board is phenolic like the transmitter board was, and the transistors are actually soldered to the board, rather than being socketed as in the rest of the set.

The board built up quite quickly, having a lot of repetitive wiring for the 8 control channels. The finished board then gets installed into a metal frame/shield which holds the remote receiver power transformer and a stepping relay used for the power and volume functions. The unit also includes a small signal strength meter used for tuning the 8 channels for best operation.

I decided to test the remote control subsystem on the bench before moving on with the build, and I am glad I did. I began by finding the appropriate pins on the molex power connector and connecting the primary of the transformer to 120 V power. Power supply rails came up OK, and I was able to tune 6 of the 8 adjustable coils (using the built in meter) to get all functions except channel down and tint green operating. The channel down function seemed completely "deaf", with no signal indication on the meter at all, and the tint green function showed a strong signal when the transmitter button was pushed, but no click could be heard from the corresponding relay. :scratch2:

A couple quick checks showed an open coil winding on the tint green relay. The relays used here are SPDT contact, 12VDC coils, with a DC resistance of ~1k ohm. Was glad to see that they were nothing exotic that couldn't be replaced, but a close examination of the open relay showed the coil wire broken right at the base pin where it entered the inside of the relay. Luckily, it was the outside end of the winding, so I was able to carefully unwind a single turn and reconnect the wire to the pin, which restored proper operation of the tint green function.

The channel down issue was more of a puzzler. a check with a scope at the output of the preamp circuit showed that a proper signal WAS being received through the microphone, ruling out a dead transmitter channel. A quick check showed all the proper components installed, and injecting a small DC signal into the relay coil drive transistor's base showed that the transistor WAS capable of turning the relay on and off. That left only the LC tuned circuit for the affected channel. The 680 pF silver mica capacitor was tested, and found to be OK, which left just the tunable coil. An identical coil (Heath p/n 40-842) is used in the power/volume channel, and preliminary DC resistance checks between the 2 showed similar result (40.8 ohms vs 41 ohms), with the "bad" coil showing the slightly lower value. Shorted turn maybe?

I swapped the coil from the power channel into the channel down position, and sure enough, it now worked fine. :yes: A comparison of the 2 coils using the ringing test function of a VA62 showed a clear difference between the 2, confirming the diagnosis of a shorted turn. Now what to do about it?

The parts chassis I got from Tim didn't have the remote option, so a donor coil wasn't easily available. The coils are typical adjustable types, wound on a fiber form, but the high inductance needed due to the relatively low frequency requires a ferrite "pot core" over the outside of the winding, as well as the adjustable ferrite slug inside. The pot core would need to be removed to examine the coil more closely, and attempt a repair. The pot core was held onto the coil form with a blob of epoxy adhesive that was quite resistant to scraping or picking at it, and I didn't want to risk damaging the core or the coil form by mechanical methods of removal. I placed the coil inside a small jar, with a few mL of dichloromethane (just enough to submerge the epoxy) overnight, and by the next day, the epoxy literally fell off freeing the pot core. The cause of the problem was easily found, a small "ding" in the side of the winding, which exposed bare copper on a couple wires and caused a shorted turn. It must have been that way from the factory, as the area was completely protected under the ferrite shell. Careful separation of the wires and a drop of insulating varnish restored the coil to proper function. The pot core was glued back on, the coil was installed into the receiver, and now all 8 functions were working!

Hopefully, the 2 bad components in the receiver aren't an indication of component problems in the rest of the set, or there may be a LOT of troubleshooting ahead. :sigh:

Up next, work begins on the heart of the build--the main chassis!

Wow. Amazing journey you are on. Thanks for the details and great pics...

Onto the 3rd volume of the assembly manuals, the Main Chassis.

The first couple bench sessions involved in the chassis construction were strictly mechanical work. LOTS of parts to be installed onto the vertical metal chassis pan. Terminal strips, power transistor sockets, filter caps, various transformers, module connectors, pots, switches, shields, and 3 factory wired sub-assemblies for IF, AFT, and High Voltage. The nut starter and 1/4" nutdriver got a real workout! :D

The chassis takes up a fair amount of space on the bench, and needs to be repositioned as assembly progresses to different areas. The heavy power transformer is one of the first parts that get installed, and it allows the chassis to be stood up in a vertical position when needed.

Assembly was pretty uneventful until it came to the HV assembly. Despite coming to me still in it's sealed box, it needed a little bit of rework to repair a broken terminal strip, a wire that never received any solder at the factory, replacement of a large electrolytic cap, and cleaning the leached sticky plasticizer from the 2nd anode cap (which I may end up replacing entirely at final assembly). The workmanship on the factory wired parts of this set was not very good at all, with a few spots of burned or melted insulation, somewhat haphazard lead dress, and a few random solder splashes which were found and removed. Probably equivalent to most assembly line wiring jobs of the day, I guess. :thumbsdn: The 3CU3 HV rectifier tube (Sylvania branded, FWIW) was rattling around loose inside the cage, free from the socket but still firmly connected to the flyback lead. Luckily it was unbroken, as were the flyback and other parts inside the cage. The tube was tested and reinstalled. Finally the reworked HV unit was bolted into place, completing chassis mechanical assembly.

I did make a minor upgrade to the set, using modern "Sil-Pad" rubber type thermal pads on all the power transistors rather than the plain mica washers and clear silicone grease that Heath provided. I replaced the thermal pads on the sweep SCRs of the HV assembly, as well. The 2 multisection twist lock caps were thoroughly reformed on a power supply and tested before installation. All the other smaller electrolytics were replaced as a precaution.

Next up--chassis wiring begins!

The chassis wiring gets installed in 3 stages, starting with routing and connecting the leads from 3 transformers (power, vertical output, and CRT filament) previously installed on the chassis, and running various individual wires between different points as instructed. These are individually cut to length from bulk wire, stripped, routed, and connected.

The second stage of chassis wiring involves the installation of prefabricated wiring harnesses and multiple Molex type connectors used to connect to components mounted off-chassis. The CRT socket harness is also installed at this point.

Finally, all the chassis mounted electronic components (resistors, caps, diodes, etc.) are put into place and soldered. All together, the chassis wiring was completed in 4 bench sessions, totaling around 9 hours. Easily the most demanding work of the project so far.

The pictures attached here are from the early stages of chassis wiring. More to come...

Very neat work, beautiful job so far. I can't wait to see it finished!

Thanks!

Here are some pics of phase 2 of chassis wiring, the installation of several prefabricated wiring harnesses and connectors.

I added a few black nylon zip ties to tie the harnesses together for improved support and a neater appearance. I also trimmed a few leads from the harnesses that were longer than they needed to be. Most wires were just perfect as provided, and the prestripped wiring goes in much faster than the short individual wires done previously.

Up next, completing the underside of the chassis with a LOT of components....